My lesabre has 40k on it so im hoping I have a few miles before having to deal with the uim.
Now when I do is plugging the ports the best move ?
If so can someone give me a step by step including the style and size of tap and plug and type of silicone ?
Also should I still chg the UIM and use the smaller dia pipe or just use my old UIM and chg the UIM gasket ? I assume you CAN buy just the gasket ?
Thx
How many miles before these usually start leaking ?

If you are looking to plug the UIM. I use a rat tail file to rough up the interior of the ports being plugged. Then a lot of brake clean to ensure no oil/additives that are in the coolant for lubrication of the water pump. After ensuring the UIM is dry, I fill with JB weld, ensuring to get non on the sealing surface. As the gasket still needs to seal to the LIM. I have also in the past put some in the holes on teh TB side as well for added measure. Give it plenty of curing time and reinstall.

Bill,
I assume I could use a Dremel with a burr to rough it up right ? Then how many tubes of JB do you need ??
Also should I still use the nickle method to fill the UIM and seal with silicone ?
Doesnt the JB take a long time to harden ??
Now you are using the JB on the UIM or on the holes in the LIM ?
If its the UIM you are plugging do I still need to plug the LIM ?
What do you mean by " i put some in the holes on the tb side too ??

I also assume I can use the old UIM but I need a NEW UIM gasket

I don't appear to have pics of this at the moment. Odd, yes.

Locate the two holes on the UIM (black manifold) where the coolant feeds from the LIM up past the EGR hole in the UIM to the TB. I fill those holes at both ends. The reason for that is to try and get the JB Weld down into the holes and ensure that no coolant can possibly slip by it and get to the EGR area.

I do not block the LIM unless I take it off the engine. Because that requires drilling and tapping and using 1/4" NPT pipe plugs. I rinse the coolant passages well to ensure no metal goes into the intake.

Not sure what nickle trick you are talking about. But the non SC'd motor lim does not have a recessed area to tap in dimes for the coolant block trick that many of us use to block off the LIM.



On using a dremel. Sure you can. Just make sure the surface is rough and not smooth.

ok i saw someone post here that they drilled and tapped the lim while on the car, then took 2 nickles and they fit perfect in the uim holes and they siliconed them in, replaced
ever see this ?

1) how many tubes of JB does it require ?

2) how long does it take to harden ?

3) you are saying to leave the LIM holes UN plugged if I use your method ?

4) Do I need a NEW UIM gasket only and use my exsisting UIM ?

5) do those holes in the UIM make a big U so they are connected or do they just go straight up and dead end so they are two seperate holes ?

6) my car has 40 k on it, at 25 k I changed out the red DEx and replaced with green mix all Prestone, how many miles before I can expect to see any UIM or LIM problems ?

Thanks so much

No, please link me if you can find it.

1) how many tubes of JB does it require ?
Which tubes are you aiming to buy? They make a 5 minute and a non 5 minute version. Advance Auto and walmart sell big tubes and little tubes. Get two 5 minute packs and you should be good.

2) how long does it take to harden ?
See directions on package. It'* 5 minute working time..but you better move faster than that.

3) you are saying to leave the LIM holes UN plugged if I use your method ?
I do.

4) Do I need a NEW UIM gasket only and use my exsisting UIM ?
I would use the same gasket, same uim.

5) do those holes in the UIM make a big U so they are connected or do they just go straight up and dead end so they are two seperate holes ?
They don't actually U. They got to the TB, The TB makes the U
See the two holes (SC, but holes in same place)


See the slot at the bottom of this TB, that'* the u bend for it. (SC, but same basic thing)


6) my car has 40 k on it, at 25 k I changed out the red DEx and replaced with green mix all Prestone, how many miles before I can expect to see any UIM or LIM problems ?
Coolant has nothing to do with gasket from my experience. The plastic gaskets get warm and warp. I did new gaskets with a full flush and in 20K miles they were beginning to bow like the old ones. Get aluminum framed gaskets in there and never worry again.

Here is an old thread, I think its the original, wish I would have seen this prior to doing my gaskets.
https://www.gmforum.com/showthread.p...ght=UIM+mod%2A

bill, I THINK it was Danthrus'* thread that showed and told that a nickle fits perfect.

1) you would really use the old UIM gasket ??

2) I assume when you talk about the aluminum gaskets you mean the LIM right ?

3) so if i block the UIM holes and leave the LIM holes there will not be any air blocks or any problems ??

Thx again

To put you at ease. There is a member Tallbump that is running the exact method I'm suggesting to you. He'* had the car for I think 4 years now.

Aluminum LIM gaskets. I reused the UIM and it'* gasket, filled the UIM coolant tubes with JB Weld and let it cure good.

Since doing that, I've learned that you can get 1/4" pipe plugs and drill/tap the LIM at the ports. You go slow and keep test fitting the plugs to have them be tight.

In reality you can do it either way.

Here'* a little candy for you.

Modifying an LIM can be done for a few different reasons. Better air flow, better coolant flow, keep an L36 from hyrolocking etc etc.

Cleaning the LIM:
I have found that working on anything car related is easier when clean. Take a moment and clean the parts. Typically I'll use Simple Green or Purple Power to degrease an item. However when it'* available a pressure washer makes quick work of cleaning and gives you a bath at the same time. After drilling/tapping and grinding on your manifold, you should rinse it with water and air dry. This will keep anything out of the rest of your motor and cooling system. It is assumed your manifold is off for all the below items.

Coolant passage blocking:
There is a small loop in the coolant system that brings coolant up out of the LIM into the UIM or SC and into the throttle body. This loop is considered by most to be pretty worthless. It may have a purpose in below freezing temps where a throttle body might ice up. In all the research I've done, it'* only been found to potentially be a problem at the north and south poles. The heat reduction to a TB by doing this is minimal, if even measureable. This is commonly done for Gen V swaps to stop the flow before hitting the throttle body adapter. Also in NA cars to keep coolant out of the plastic manifold that can rupture and fill the cylinders with coolant.

Here is an L67 LIM. See the two recessed holes. Those are the ports we are speaking about. On NA manifolds and many L32 manifolds those are not recessed.


You drill with the proper drill, then tap with 1/4" NPT tap.



Using a little pipe sealant you insert the headless 1/4" NPT pipe plug. Tap it slowly and keep trying the plug. Being NPT, the threads are tapered, you don't want to tap too far and have a loose plug.



Increasing Coolant Flow:
Now if you have done the above and blocked the TB coolant ports, your coolant flow is reduced slightly. In our 3800 motors, it is known that cylinders 3 and 4 (both middle cylinders) run hotter than the other four because they are in the middle of the heat sandwich. I like to increase the flow from the rear head to the front head (thermostat area) by opening up the area behind the endcap on the LIM. This cap is under the throttle body. Have a dealer only rear intake coolant cover gasket (24505049) on hand and remove the two 8mm bolts holding the cap to the manifold.


I find that hogging it out a bit to look like this helps keep heat from building in the rear head.
Before:

After:


Post SC air temp sensor:
If you have an interest in an air temp sensor, the best sensor appears to be an early 90'* 350 TBI air temp LIM sensor. Looks like this


They appear to be 3/8" NPT and the best placement appears to be in the end of the LIM near the #1 runner.


Porting the runners:
This should only be done if head porting work has been done. Otherwise if you gasket match the LIM runner and not the head, the air hits the edge of the head and that causes a disruption to the air flow.
I use an old gasket and bolt it to the LIM, then using a carbide bit, open the port to the gasket size, and smooth the rest of the runner from there. Sorry, no pics.

Opening up the inlet:
If you are going from a Gen 3 to a Gen V or intercooling, you will want to open up the LIM'* air inlet. This is really dependent on the size/shape of what you are adding.

Bill,

1) CAN i DRILL AND TAP THE lim W/O REMOVING IT ??

2) If not can I just fill the UIM and leave the holes in the LIM alone and they will not cause any problems, coolant flow or air lock ??

3) I would be safe re-using the UIM gasket ??

What im thinking is I could drill and tap the LIM while on the car and vaccum out after to remove chips, if you dont think this is a good idea maybe just fill the upper ??