Blocked TB passages at the LIM mod (S2) - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 09-18-2007, 12:29 AM   #1
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Default Blocked TB passages at the LIM mod (S2)

If you have an intercooler that blocks the TB coolant passages or an HVII, you may be interested in this.

Somewhere along the line, I saw turbocharged400sbc say that if youíre blocking off your TB passages, youíre really limiting coolant flow in the LIM. He also said that you could modify the wall in the LIM by the coolant bypass plate (by the EGR) to remedy this deficiency.

When my engine was in my old 95, with a HVII'ed L36, my engine would get hot get up to 200* pretty easily with a 180 stat and no air in the system. It was also more difficult than normal to get cool...
Before I put the engine together, for the new car, I took off the LIM coolant bybass plate, cut the wall in the LIM about a half inch deep on the top and bottom , and broke a 1/2" x 1/2" sized piece off that wall. This was just to improve coolant flow at the bypass plate since there was no flow to the TB.
My car now does not have a cooling problem anymore in rush hour and it hasnít made it to the 200 mark yet (180 stat).

Bottom line: If your TB passages are blocked in a Series 2 and youíre having a hard time keeping it cool, modify the wall behind the bypass plate in the LIM and it should help.
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Old 09-18-2007, 12:43 AM   #2
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First I heard of that.
I have mine blocked with no heat problems at all.
I run a 160 stat and the temp never goes above 185 even in 90 degree weather.
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Old 09-18-2007, 08:10 AM   #3
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Very interesting and this makes good sense.

25 degrees over the T stat is a bit high in my opinion. With a 180F the highest I've seen my coolant is 200 in 95-100F with 95% humidity. (It'* not a dry heat and feels like 150F to a car). Most of the time in the 90'* I see 185-190F.

This is definately going to get looked into as a future mod to keep the temps more regulated.

NA owners may also want to look this over as if may reduce some of the stress in the EGR port area if the ports are not plugged.
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Old 09-19-2007, 01:26 AM   #4
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The higher temps are caused by limitation with the radiator cooling not the LIM passages IMO.
As soon as the air flow resumes in hot temps my coolant drops back to 160 F.
It only climbs to 185 when stopped in traffic or sustained high speed driving when the trani temp climbs to 200 F. My trani oil circulates thru my rad as well as my auxillary cooler.

Not doubting that opening up the TB passage partition will help but I haven't noticed a problem.
Might be worth a try thou next time I have it off. Don't think it would hurt.
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Old 09-19-2007, 08:03 AM   #5
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From my testing on a S1 L67, you don't want to block anything in the TB area for a daily driver. The hottest portion of the SC under boost is the inlet. It gets hotter than the coolant. The M90 should be similar.

My opinion on the L36 is that the coolant would extend the life of the EGR stovepipe area by keeping it cooler on hot days. This is just a theory, but it makes sense to me.

Talking daily drivers here, of course.
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Old 09-19-2007, 09:44 AM   #6
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Paul...Aren't your fans programmed to come on slightly above your T stat? Or were they programmed to be at 185F?
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Old 09-19-2007, 10:48 AM   #7
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Yes Bill, I fully agree with not blocking the TB passages if your EGR hasn't been removed and the EGR passage plugging with JB weld. Passing hot 500 F exhaust into the TB will tend to warm it up a bit.

Yes Boosty, my fans are programmed to come on at 160F.....further supporting my theory that the radiator core was not designed to cool below 185 when the engine is under load, the outside temps are high and the trani oil temps are high.
Even if outside temps are high but the engine has not been driven hard, it will maintain 160 temp.
For instance, racing at Woodburn, the temp never went over 165F because the runs were brief but on the highway at sustained 85 mph speeds in 90F temps, the trani temp went to 200, the engine temp went to 175 but when I stopped and the air flow decreased (even with the fans running) the temp would rise to 190.
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Old 09-19-2007, 10:52 AM   #8
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Old 09-19-2007, 02:01 PM   #9
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Quote:
Originally Posted by 2000SilverBullet
The higher temps are caused by limitation with the radiator cooling not the LIM passages IMO.
As soon as the air flow resumes in hot temps my coolant drops back to 160 F.
It only climbs to 185 when stopped in traffic or sustained high speed driving when the trani temp climbs to 200 F. My trani oil circulates thru my rad as well as my auxillary cooler.

Not doubting that opening up the TB passage partition will help but I haven't noticed a problem.
Might be worth a try thou next time I have it off. Don't think it would hurt.
Just because your temps will drop when you get moving dosen't mean the radiator is the problem.
If the coolant isn't flowing to the correct places at the correct rate, it'* not going to cool the engine properly.
Blocking the TB passages changes the direction and flow of coolant from how it was originally intended.
IMO you won't know if your stock radiator can maintain a 160* temp in harsh conditions untill your coolant is flowing closer to stock.

As far as the L36 goes. You will never ever have to worry about a UIM failure if you block the TB passages at the LIM. Then if you modify the wall behind the coolant bypass plate, you can get the coolant flowing similar to stock. My HVII blocks the TB passages at the LIM if anyone reading this doesn't know.
I can understand how the EGR heats up the aluminum casing of the superchargers and transfters heat to the TB. But, I don't see the composite L36 UIM transfering heat to the TB to the same degree.

I'm just offering this as something I read about, tried, and worked in my application. Your not really going to know if it will help your specific application unless you give it a shot.
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Old 09-19-2007, 02:28 PM   #10
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Would you say it'* a restriction when the TB ports are not blocked? I'm wondering here if this might be the most restrictive point of coolant flow beyond the T stat.
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