Intake plenum still usefull?? - Page 2 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 10-02-2007, 10:51 AM   #11
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Quote:
Originally Posted by BillBoost37
How about another option. Bob Dillion had filled the coolant passages on one of the UIM'* and was running it. Also I believe WillWren and EK98 had one that was also filled. There was a relief hole to be drilled, but otherwise I think it worked fine.

That could be your quick, low cost fix and then follow up later on with a new APN sleeved UIM to restore the coolant flow.
Good point, Bill. I forgot all about Bob'* coolant plug method. I was thinking that what Bob did was to plug the coolant bores in the LIM. James should install his new LIM gaskets too, in case those are gone or about to go.

He needs to get wrenching if he plans to be driving tomorrow morning. And he will need to use a quick set epoxy to set the plugs rather than regular JB Weld which requires an overnight cure at the least. This will reduce the temperature resistance of the adhesive by about 300*F, but it still might get him by for a little while. Trying to get this done well in a day is not gonna be easy.
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Old 10-02-2007, 12:07 PM   #12
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Found Bob'* method:

Quote:
Originally Posted by Bob Dillon
OK, guys, I think this problem is solved. Better yet, it'* quite a bit simpler than the sleeved upper, what with the core problem, shipping costs, and turnaround time.

To accept this repair as the final and easier solution, however, we need to accept as an article of faith that the throttle body heating in the Series II is superflous. After doing some thinking, some netsurfing with our brethren over at the GP site, and thinking about some anecdotes provided by members here who live in cold climates like northern NY state and Minnesota, I think the thinking is valid.

When I got the spare LIM from Mark (Vital49), I degreased it and ran it over to my buddy with a shotblasting cabinet, and it came back looking like a new one. As you know from my previous posts in this thread, I discovered that the two coolant passages in the LIM were just a bit too large to tap for 1/8" pipe thread, which would have been perfect. Pipe threads just do not leak.

However, no go, I tried the tap and 1/8" pipe plugs, and they wouldn't tighten down enough. So, I came in and surfed the Motormite/Dorman site, and ordered some 1/2" core plugs from my NAPA guy. I drilled the coolant passages out in the LIM out to .500 from their as-cast .375. Next, I mixed up some JB weld, buttered up the plugs well, and drove them into place with a brass hammer and a 1/4" socket extension. Next, in an abundance of caution, I filled up the cups with JB weld to the LIM surface. Pix below of the manifold drilled, and then with plugs inserted.





As I was talking about this problem with Boosty and afterward mowing my grass, an idea came to me. OK, we can plug the LIM easily, but the UIM is plastic ; that'* the whole problem, and plastic is easy to drill. Hmmmm. I inspected the UIM core I have and sure enough, the holes in the coolant passage are .375 as well, and there'* a lot of meat around them. Yup, you guessed it, they drill to .500 easily. The picture below is the upper with coolant passages drilled to .500 and the same Dorman core plugs inserted. They could easily be epoxied into place.



So, it occurs to me we have two solutions that will work. We need to keep in mind that GM very nearly got this problem right. Most upper failures occurred around 60,000 miles or better, and some (post 99) haven't failed yet.

Best of all, these two are what might be called "driveway solutions." You can tear the car down and the UIM problem can be fixed overnight with tools everyone has and parts everyone can get easily. No shipping, no core problem, just a simple fix and button 'er up and go, no more worries.

The stovepipe solution? An easy one, and it'* Bill'* .750/510 one. On older cars with the .750 bore, one simply removes the .750 stovepipe carefully and JB welds it to the EGR bore. We don't have to worry about coolant leaks; either plugging the UIM or LIM (or both for our more cautious mechanics) negates the coolant leak problem, and the .120 gap in place with the .750/.510 stovepipe ensures the new sleeve/former stovepipe isn't toasted.

....

So, we may have simplified this process quite a bit. As I did with the original sleeved upper, my car is going to be the test mule. I've ordered gaskets, and since I have to change the heater core soon, I figure I might as well ruin a whole weekend, and will do so as soon as the weather breaks.

A few things in closing: thanks to Mark (vital49) for shipping me this LIM for a few bucks plus freight.

Secondly, if these ideas sing to you and you haven't done anything about your upper yet, I'd do two things: Run down to the auto store and get 4 Dorman (or Motormite) PN 555-005 plugs and toss them in your toolbox.

...
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Old 10-02-2007, 02:15 PM   #13
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Right.

My suggestion is to do what some of the supercharged guys do. Plug only the UIM being that it'* a temporary fix. Using the JB Weld Qwik should be fine..IIRC and you'll want to double check it'* good for around 300F degrees.

Plug the old UIM only. That way no coolant will get into the EGR and ensure a good gasket is used as this area will probably receive a bit more pressure.

Meanwhile, order the APN and drive to work.

When the new one arrives..drain off about a half gallon or so of coolant and swap uppers.
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Old 10-02-2007, 06:02 PM   #14
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If you opt for the plugged passage fix, James, please do not delay in obtaining a reduced diameter stovepipe and a sleeved UIM, either by purchasing an APN kit, or by finding a Dorman .510 x .750 pipe from a BC member, and a sleeve from Bob or me to repair your own.

You will notice in Bob'* post, that he has installed a steel sleeve in his upper along with discussing the use of a .510" stovepipe. Those components are necessary to protect the plastic EGR bore which is more prone to heat damage with plugged passages because there is now no coolant flow around the bore to remove excess heat.

If you do the plug fix without adding a sleeve and a reduced diameter pipe, you will be subjecting the failure prone area around the EGR bore to more heat than it was (poorly) designed to withstand. The heat may cause warpage that results in a coolant and/or vacuum leak at the UIM/LIM interface.

The safer course would be to drill and plug the LIM bores. Once they are tightly sealed off, there is no source of coolant to damage the engine from that area. Vacuum leaks would still be possible from warpage, but they won't ruin your engine. The downside of plugging the LIM is that it will make it difficult to restore coolant flow without some careful machine work or replacement of the LIM with one from a junkyard.
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Old 10-03-2007, 06:21 PM   #15
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Er, I haven't been keeping up on the BC for a while, but I have a few thoughts about this new 'solution' to the problem. This is more me thinking out loud than anything, so feel free to correct me if you think I'm wrong.

1) plugging the coolant lines - I've never seen this as a good thing, as you're stopping a leg of your coolant system from moving coolant. Coolant is supposed to move up one side of the LIM, through the UIM, through the TB passage, and back down through the opposite passage. WIth this blocked off, coolant now sits without movement (and without removing heat) in the LIM. Blocking at the TB is a worse situation, as heat is trapped in the UIM.

2) coolant cooling the egr - I'm not sure I follow this line of thinking - in order for the coolant to be actively cooling the UIM, the coolant would have to be cooler than the nylon (not plastic) immediately surrounding the coolant passages (immediately... as in the walls of the coolant passage, if there was no coolant present). However, our observed failures tell us the opposite - the largest degradation in the UIM occurs directly between the EGR passage and the coolant passages. This isn't a coincidence, it'* because you have more heat trapped between those areas than any other part of the UIM (i.e., the coolant is heating that region of the UIM, so it'* already hotter than other areas the same distance from the EGR passage). The coolant isn't aiding the heat transfer of the EGR passage, it'* making it worse.

3) Sleeving the upper - I've got very mixed feelings on this solution, which I've avoided posting in the past, but I'll throw my thoughts out there. The idea of sleeving the upper sounds good, and it certainly makes it harder for coolant to physically enter the EGR passage, but I think we're doing more damage to our UIMs because of it. Why? Well, I think placing a big piece of metal up against the nylon walls of the EGR passage is acting as a heatsink - for the EGR passage. Let me see if I can explain my thinking - the EGR stovepipe is in place to prevent the EGR gasses from directly contacting the nylon, right? The air gap is provided because air works as a pretty decent insulator, and the air gap also allows convection to take place. The air will find it'* way back into the UIM, and continually cool the EGR stovepipe. In my original UIM job (I can post pics if anyone is interested), the mess that is EGR and PCV had caused the entire air gap to be blocked from inside of the UIM - enough so that the pressed fit EGR stovepipe came out with the UIM, not the LIM. In any event (I'll avoid a side-rant), adding a piece of metal that comes directly into contact with the upper seems to be a move in the wrong direction to me - you're again basically adding a heat sink - the thermal conductivity coefficient of the metal is much higher than that of the nylon - so the metal will heat up more than the nylon ever would have on its own.

So, in this state, you've just added additional heat to the area that we're trying to protect - That said, with the increased air gap (of the combined sleeve / new diameter pipe fix), there may be a large enough volume of air that the convection will protect the sleeve from getting too hot... but I don't know. I don't think that any of us know, and that'* what bothers me about this fix.

Of course, the physical barrier between the coolant passage and the EGR passage is a very good thing - but I'm extremely curious what happens to the UIM behind this sleeve.

Okay, those are the top 3 thoughts that I've had on my mind (#3 for some time now). Feel free to question my thinking... again, I'm just thinking out loud here.

As for a quick fix, I would not recommend modifying your lower intake manifold. If necessary, I'd find someone that would be willing to spend $150 on a dorman intake (now comes with a reduced diameter stovepipe, btw) as either a gift or a short term loan, and get it done right. I understand the situation you're in... completely.
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Old 10-03-2007, 11:02 PM   #16
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hey guys, thanks for all the help. A buddy of mine came up with just throwing some jb weld around the "ever so slightly" degraded area of the stove pipe inside the plenum, sanded it out, put in some more and made it fit really tight. I know this is not a the best thing to do, but i plan to order the APN kit tuesday of next week so hopefully it keeps up 4 me till then. One more thing, is there anything really wrong with doing this for a week or two?? Thanks again for all the help
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Old 10-04-2007, 01:55 AM   #17
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Quote:
Originally Posted by mkaake
Er, I haven't been keeping up on the BC for a while, but I have a few thoughts about this new 'solution' to the problem. This is more me thinking out loud than anything, so feel free to correct me if you think I'm wrong.
Good to have you back. And this is no proper welcome, but I must disagree with several of your assertions.

Quote:
Originally Posted by mkaake
1) plugging the coolant lines - I've never seen this as a good thing, as you're stopping a leg of your coolant system from moving coolant. Coolant is supposed to Wmove up one side of the LIM, through the UIM, through the TB passage, and back down through the opposite passage. WIth this blocked off, coolant now sits without movement (and without removing heat) in the LIM. Blocking at the TB is a worse situation, as heat is trapped in the UIM.
I don't advocate plugging the cooling system either, but not for the reasons you cite. That is because the primary means for coolant to move from the rear (firewall side) chamber on the driver'* end of the LIM is through the bypass cover that sits under the throttle body into the thermostat housing and out to the radiator when the thermostat opens.
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I don't like plugging the LIM or UIM coolant passages because the bypass is located near the bottom of both chambers, and when the LIM is plugged as shown above, air is trapped in the rear chamber and has no way to be bled out. That is why when this method was first discussed here on BC, I advocated a bleed be installed high on the rear chamber if the plugging method is used.

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I did not bring up the need for an air bleed as James was looking for a fix that only needed to work for a few days.

Quote:
Originally Posted by mkaake
2) coolant cooling the egr - I'm not sure I follow this line of thinking - in order for the coolant to be actively cooling the UIM, the coolant would have to be cooler than the nylon (not plastic) immediately surrounding the coolant passages (immediately... as in the walls of the coolant passage, if there was no coolant present). However, our observed failures tell us the opposite - the largest degradation in the UIM occurs directly between the EGR passage and the coolant passages. This isn't a coincidence, it'* because you have more heat trapped between those areas than any other part of the UIM (i.e., the coolant is heating that region of the UIM, so it'* already hotter than other areas the same distance from the EGR passage). The coolant isn't aiding the heat transfer of the EGR passage, it'* making it worse.
I agree that the area around the stovepipe is the hottest place on the UIM and I agree that that heat is what causes the composite to fail. But I cannot agree that the area around the hot stovepipe is hotter because of coolant flow nearby. You can bet a $1 that the reason for the complex casting creating cooling flow around the hot EGR pipe bore is to provide cooling for the EGR bore, and not because GM wanted to design a more expensive and circuitous route to warm the throttle body.

Consider coolant at 200F. Consider that with the coolant flowing, the composite material around the coolant passages cannot easily increase in temperature above 200F. You can prove this to yourself by boiling water in a paper cup over an open flame if you wish. For the purpose of discussion, assume a temperature of 600F for the outer surface of the EGR stovepipe. With newer stovepipes, where an air gap exists between the hot metal pipe and the composite walls of the UIM, radiation probably plays a more important role in heating the walls than conduction or convection. But for the older pipes, where the gap was only a few thousandths, the oil vapors from the pcv system quickly build up on the stovepipe and form petroleum coke, often trapping the pipe (as you describe below) and forming a conductive path from the hot pipe to the vulnerable composite material of the UIM. Now the temperature of the composite material near the pipe is close to 600F. A flow of 200F coolant nearby will without question lower the temperature of plastic near the hot EGR pipe and help to preserve the composite compared to, say, no coolant. This is, in my opinion, exactly what happens in most early failures. An examination of the cooling system will reveal that the coolant passages to the throttle body are the highest point in the system and the first to be starved of coolant if the system is not completely bled of air. You may run for months or years with a coolant level below the throttle body ports and never know it. But the UIM may be suffering serious heat degradation.

Quote:
Originally Posted by mkaake
3) Sleeving the upper - I've got very mixed feelings on this solution, which I've avoided posting in the past, but I'll throw my thoughts out there. The idea of sleeving the upper sounds good, and it certainly makes it harder for coolant to physically enter the EGR passage, but I think we're doing more damage to our UIMs because of it. Why? Well, I think placing a big piece of metal up against the nylon walls of the EGR passage is acting as a heatsink - for the EGR passage. Let me see if I can explain my thinking - the EGR stovepipe is in place to prevent the EGR gasses from directly contacting the nylon, right? The air gap is provided because air works as a pretty decent insulator, and the air gap also allows convection to take place. The air will find it'* way back into the UIM, and continually cool the EGR stovepipe. In my original UIM job (I can post pics if anyone is interested), the mess that is EGR and PCV had caused the entire air gap to be blocked from inside of the UIM - enough so that the pressed fit EGR stovepipe came out with the UIM, not the LIM. In any event (I'll avoid a side-rant), adding a piece of metal that comes directly into contact with the upper seems to be a move in the wrong direction to me - you're again basically adding a heat sink - the thermal conductivity coefficient of the metal is much higher than that of the nylon - so the metal will heat up more than the nylon ever would have on its own.

So, in this state, you've just added additional heat to the area that we're trying to protect - That said, with the increased air gap (of the combined sleeve / new diameter pipe fix), there may be a large enough volume of air that the convection will protect the sleeve from getting too hot... but I don't know. I don't think that any of us know, and that'* what bothers me about this fix.

Of course, the physical barrier between the coolant passage and the EGR passage is a very good thing - but I'm extremely curious what happens to the UIM behind this sleeve.

Okay, those are the top 3 thoughts that I've had on my mind (#3 for some time now). Feel free to question my thinking... again, I'm just thinking out loud here.
Ken Spragg got this right many years ago when he developed the KenCo kit comprising a steel heat shield and a reduced diameter stovepipe. The primary purpose of the sleeve is to reflect radiant heat from the stovepipe. The reduced diameter stovepipe provides an air gap of .125" that keeps the primary heat transfer as radiation rather than conduction or convection. There is no question that this method is effective. Look around your car at all the places that heat shields are used. I assert that your notion that the plastic will be hotter under the metal is incorrect. Make a test yourself to prove it. Take a piece of wood, wrap half of it with aluminum foil and leave the other half bare. Place the wood 12" from a 500F heat source for, say, an hour. Feel the bare wood with your hand. It will be hot. Now feel the foil, or the wood under the foil. It will be cool. That is how heat shields work. And that is how the sleeve works in the UIM.

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I am certain that the above test will work because I have made it myself in my own living room. When I burn wood in my little parlor stove, the wood trim nearby used to get very hot to the touch. Now, with this simple heat shield, although the woodwork is still pretty warm above the foil, the foil itself and the wood beneath it remain cool to the touch after hours of exposure to heat around 4-500F.

You are certainly correct that we want to provide as large an air gap as practicable, because air is an excellent insulator and because any coke buildup will take a long, long, time indeed to bridge .125".

Quote:
Originally Posted by mkaake
As for a quick fix, I would not recommend modifying your lower intake manifold. If necessary, I'd find someone that would be willing to spend $150 on a dorman intake (now comes with a reduced diameter stovepipe, btw) as either a gift or a short term loan, and get it done right. I understand the situation you're in... completely.
While the best quick fix for James is now a moot point, plugging the coolant flow for a week or two would have probably worked out okay for him. I am thinking that would have been a lot safer solution than what his buddy did for him. And, finally, regarding choice of UIM kits, I maintain that the APN kit with a heat shield and a price $35 less than a Dorman is the best off-the-shelf choice. I am not saying that a Dorman UIM kit is a bad choice. We have not heard of any any Dorman UIMs failing when used with a reduced diameter stovepipe. But, we have also never heard of a KenCo kit failing, or an APN upper failing. We have seen 99+ GM bare composite uppers fail with 5/8" diameter stovepipes.

You are right that no one has posted evidence here regarding the relative roles of the various means of heat transfer at play in this situation. We have discussed placing temperature probes on the backside of UIM heat shields to see how hot they get in service. Bob Dillon even found a source for a small probe. But none of us has GM'* budget to accurately measure and evaluate these effects. About the best we can surmise short of paying the $ and doing the tests ourselves, is to observe the efficacy of the heat shield and smaller pipe fix. The evidence to date, and the technical logic supporting their application is sufficient for me to use these improved methods for my own vehicles and to recommend them to others.
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Old 10-04-2007, 04:29 AM   #18
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Quote:
Originally Posted by 3064datazz
hey guys, thanks for all the help. A buddy of mine came up with just throwing some jb weld around the "ever so slightly" degraded area of the stove pipe inside the plenum, sanded it out, put in some more and made it fit really tight. I know this is not a the best thing to do, but i plan to order the APN kit tuesday of next week so hopefully it keeps up 4 me till then. One more thing, is there anything really wrong with doing this for a week or two?? Thanks again for all the help
I am sorry, James, that we could not come up with a quicker, easier fix for you. Hope the new job is going well.

If he made the stovepipe fit really tightly against the JB weld, then that would be a bad idea. That pipe gets really hot, and it is about the worst thing you could do to fit it tightly against the plastic upper. As you say, hopefully it will last until the APN kit can be installed. Just keep a good watch on the coolant level and be careful to look for white smoke out the exhaust. If you start leaking coolant internally, your engine can be ruined in less time than it takes to receive your APN kit.

Please take time to read the Techinfo articles linked for you above. If you have time, use the search feature to learn more about how and why these repairs are made. Be sure to let us know if you need any help when it comes time to do the LIM gasket, UIM work. We are here to help.
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Old 10-04-2007, 07:50 AM   #19
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Thanks for taking the time to reply. My quick counter

Quote:
Originally Posted by bill buttermore
Good to have you back. And this is no proper welcome, but I must disagree with several of your assertions.
No problem! As I said, I'm thinking out loud here

Quote:
I don't advocate plugging the cooling system either, but not for the reasons you cite. <snip>
I did not bring up the need for an air bleed as James was looking for a fix that only needed to work for a few days.
Ah, fantastic. Believe it or not, despite having changed the gasket around that bypass, I had never taken the time to consider what it was there for... but I'll completely agree with you on this one.

Quote:
I agree that the area around the stovepipe is the hottest place on the UIM and I agree that that heat is what causes the composite to fail. But I cannot agree that the area around the hot stovepipe is hotter because of coolant flow nearby. You can bet a $1 that the reason for the complex casting creating cooling flow around the hot EGR pipe bore is to provide cooling for the EGR bore, and not because GM wanted to design a more expensive and circuitous route to warm the throttle body.
No, but I'd bet a $1 that this is what happened:

On the S1 with a metal intake, coolant flow was externally routed. On the S2, packaging constraints don't leave room for external routing - I've looked, as at one point, I planned on routing the coolant flow outside of the UIM. While I'm sure you could find a way to fit it, why bother? If you're creating a brand new UIM for the S2, and you know it'* going to be a composite (like we were, for a time, moving for all intakes), why not take the most direct route, remove 6 parts and 4 taps from the operation? Sure, you have to add the detail to the composite'* structure, but when you're designing from the ground up, that'* a moot point - if anything, you'll have long term cost savings from the smaller amount of nylon used in the UIM. This design was carried forward into the S3 intake design because it was designed to maintain the maximum number of parts from the S2 - including the lower intake. And again, moving coolant flow externally adds parts and complexity to the manufacturing process.

Quote:
Consider coolant at 200F. Consider that with the coolant flowing, the composite material around the coolant passages cannot easily increase in temperature above 200F. <snip>
If coolant was the only factor involved, than yes, I would completely agree with you - the walls would never get hotter than the coolant. With external influences, the temperature largely depends on the flow rate of the coolant. So we'll move the analysis 1mm beyond the wall of the coolant passage.

Well, actually, I'm not going to do a psuedo technical analsys, where I just create a straw man - that won't help the discussion. The only real way to answer this question is with thermocouples placed inside of the UIM between the coolant and EGR passages.

That said, if the coolant was helping to cool the UIM, then in our failed UIMs, the areas of the intake between the EGR passage and coolant passage would have the smallest amount of wear of any portion of the EGR passage.

Instead, we find that a passage opens up between the coolant and EGR passages - a full 15mm of material (if memory serves). To me, this says we have more heat concentrated between the coolant and EGR passage than in other locations on the UIM.


Quote:
With newer stovepipes, where an air gap exists between the hot metal pipe and the composite walls of the UIM, radiation probably plays a more important role in heating the walls than conduction or convection. But for the older pipes, where the gap was only a few thousandths, the oil vapors from the pcv system quickly build up on the stovepipe and form petroleum coke, often trapping the pipe (as you describe below) and forming a conductive path from the hot pipe to the vulnerable composite material of the UIM.
I don't know that I agree on the radiation vs convection at this point, but there'* no good way for either of us to prove it... so it goes . I do, however, need to point out that in my case, even though the top of the EGR port had been blocked, an air gap still existed between the rest of the pipe and the UIM.

Quote:
Now the temperature of the composite material near the pipe is close to 600F. A flow of 200F coolant nearby will without question lower the temperature of plastic near the hot EGR pipe and help to preserve the composite compared to, say, no coolant.
Unless, of course, because of the thermal properties of the nylon in use, the intake would have already been cooler than 200F 15 mm from the EGR passage. If, at 15mm, the nylon was at 100F, or even 175F, the coolant will increase the heat build up in that area.

Quote:
This is, in my opinion, exactly what happens in most early failures. An examination of the cooling system will reveal that the coolant passages to the throttle body are the highest point in the system and the first to be starved of coolant if the system is not completely bled of air. You may run for months or years with a coolant level below the throttle body ports and never know it. But the UIM may be suffering serious heat degradation.
Which actually creates a sick situation in which you can drive a blown UIM with low coolant levels, and never know it, but you fill it up one day, and within 20 miles you're done. (Which is actually what just happened to my mom).

Quote:
Ken Spragg got this right many years ago when he developed the KenCo kit comprising a steel heat shield and a reduced diameter stovepipe. The primary purpose of the sleeve is to reflect radiant heat from the stovepipe.
Eh, I'm not sure I'm buying that one just yet - color me unconvinced. I'm sure it can help to reflect radiant heat, but it can also have the opposite effect. Without knowing how hot the back side of the sleeve is though, we'll never know. *shrugs shoulders*

Quote:
The reduced diameter stovepipe provides an air gap of .125" that keeps the primary heat transfer as radiation rather than conduction or convection. There is no question that this method is effective. Look around your car at all the places that heat shields are used. I assert that your notion that the plastic will be hotter under the metal is incorrect.
Unfortunately, w/o some good thermocouples, as well as some before and after measurements, I don't think we can answer that for sure. I'd love to, I really would.

[quote] Make a test yourself to prove it. Take a piece of wood, wrap half of it with aluminum foil and leave the other half bare. Place the wood 12" from a 500F heat source for, say, an hour. Feel the bare wood with your hand. It will be hot. Now feel the foil, or the wood under the foil. It will be cool. That is how heat shields work. And that is how the sleeve works in the UIM. [quote]

Right, but for this to be a test indicative of our situation, it needs to be done with the same constraints - the same sheild material (what type of (steel?) is he using?), the same small air gap (I'm wondering how effective the radiative properties can be when there'* .125" of air gap for the heat to radiate back in to (I think conduction is going to come back in to effect a lot faster than we think), with a 1000F heat gun pointed at it.

Then measure the material directly behind the sheild before and after (and make that material nylon... because I'm not sure how it handles the heat on its own).

Again, I don't think there'* a way we can prove this with theory - I think it can only be proven one way or the other with real world testing.

Quote:
You are certainly correct that we want to provide as large an air gap as practicable, because air is an excellent insulator and because any coke buildup will take a long, long, time indeed to bridge .125".
For sure. As long as that passage is left open, we'll be in far better shape than what we are now.

Quote:
While the best quick fix for James is now a moot point, plugging the coolant flow for a week or two would have probably worked out okay for him. I am thinking that would have been a lot safer solution than what his buddy did for him. And, finally, regarding choice of UIM kits, I maintain that the APN kit with a heat shield and a price $35 less than a Dorman is the best off-the-shelf choice. I am not saying that a Dorman UIM kit is a bad choice. We have not heard of any any Dorman UIMs failing when used with a reduced diameter stovepipe. But, we have also never heard of a KenCo kit failing, or an APN upper failing. We have seen 99+ GM bare composite uppers fail with 5/8" diameter stovepipes.
I don't think we'll see much of any failures from sleeved kits. My 3800, built in late 95, with the smallest gap available, didn't fail until 140,000 miles. Just by increasing the air gap, the mean time to failure should increase (though there have certainly been failures earlier than this...). I guess my point is, increasing the air gap to what you have for these fixes would likely get the UIM through at least another 100-150k miles - and I doubt we'll have any S2'* around long enough ( *cough* 4T65 *cough*) to find out if they'll last that long.

Quote:
You are right that no one has posted evidence here regarding the relative roles of the various means of heat transfer at play in this situation. We have discussed placing temperature probes on the backside of UIM heat shields to see how hot they get in service. Bob Dillon even found a source for a small probe. But none of us has GM'* budget to accurately measure and evaluate these effects. About the best we can surmise short of paying the $ and doing the tests ourselves, is to observe the efficacy of the heat shield and smaller pipe fix. The evidence to date, and the technical logic supporting their application is sufficient for me to use these improved methods for my own vehicles and to recommend them to others.
I'd use it before using nothing. For sure.

Anyway, if you guys really want to do it, I've got about 20 ft of Type K thermocouple wire just laying un-used in my garage. Drill a smallish (1mm should do) hole in the appropriate location, cut the wire to length, solder the end together, insert, epoxy, and there you go. You'll want a nice thermocouple reader though - I've got one built in to my DMM... should be accurate enough to at least prove out a theory, no?

All of this said, I just stumbled on something that makes all of this a rather moot point - look for a new post in the 92-99 forum today.
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Old 10-04-2007, 08:07 AM   #20
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James.. I agree about filling the EGR bore area being bad. Not sure about JB Weld'* heat transfer characteristics..but I'd rather see you fill the UIM coolant bore going to that EGR area.
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