drilled thermostat and more sealant details please

[carl]

I read previous posts about locating the drill hole in the thermostat to the 12 o'clock position. This 12' o'clock is with reference to where? the top of the thermostat housing?

Also I had questions on specific sealents the LIM replacement on the 3800.
Maybe someone can do a drawing showing the application points. It could become really important.

Back when rebuilding 350 we used ''yellow snot'' (3m weatherstrip sealer) around the intake ports and rtv to seal only water/coolant related passages. The reason rtv ("blue goo" back then) wasn't used much, is that it would end up as thousands of tiny clear silicone shards in the oil pick-up screen...there were so many that it became a slicone mass clump.

I've heard mention of using RTV, GM RTV, and RTV copper.

Could someone clarify which is better to use and where?

Thanks again.

[gonzo4191]

drill a hole outside the flange and place it so the hole is sraight up at the "12 o clock" position inside the housing

[danthurs]

Why drill it? I've done dozens of thermostats and NEVER had a problem. As long as you have coolant filled up to the top of the LIM you will not have air entrapment. The only air in the system will be in the top hose and that burps out in to the radiator. Drilling is a waste of time.

[2003 SSEi]

and on your 02 you will set a check engine light because the car will not warm up quick enough as determined by the PCM

[00Beast]

My car came FACTORY with a drilled t-stat. 12 o'clock as referenced with you standing at the front of the car, the highest point in the LIM. My car has 0 issues with a drilled t-stat. Just drill a hole smaller than 1/8 of an inch, and you'll be fine. the amount of coolant it lets through is minimal, it's mainly for burping the system.

[danthurs]

Not once in 35 years have I ever had to burp a system.

Let me rephrase that, never have I had enough air in the cooling system to hold up a thermostat or cause problems with the water pump.

[GXP Venom]

Dan and I were talking about this. I believe the prime reason for factory drilling was to stabilize pressure if I remember reading at the time right.

ZZP sells them but purging air isnt even an issue stated

"A colder thermostat is an inexpensive way to lower engine temperatures. Cooler engine temps reduce KR and promote cooler intake air temps. Our thermostats feature openings 20% larger than stock for increased flow.
We also offer modified thermostats for increased performance.
Drilled thermostats- The car will still get up to the temp that the thermostat is but it will take longer. The gain in it taking longer is when your car is sitting(not running) it is cooling down. When you restart the car to race it
A 180 is the coldest stat is recommended for the N/A 3800. Using a 160, the PCM commands too rich of a fuel mixture.
A non-drilled 180 stat is recommended for the 2004+ GPs, 2000+ Bonnevilles and Regals or an engine code can be set."

This whole "purge air" idea is a local forum phenomena that doesnt have any basis in fact.

[carl]

Thanks for the t-sat feedback. My post here just got lost, so I apologize if this one ends up double posting. Actually my reasoning is closer to the following as also mentioned on the zz site:

"...Performance blasting down the ¼ mile isn’t the only advantage of having holes drilled in your thermostat. If you live in a colder climate this $11 investment might just save your cylinder heads from being cracked and damaged from the sudden dive in coolant temperature as your winter chilled radiator dumps it’s freezing coolant through your heads.

A drilled stat would be much more forgiving by providing a continuous flow of coolant and reducing sudden and drastic temperature changes."
- Andy H
Duluth, MN
1999 Grand Prix GTP
02/16/2004

And here where I am the car sets 14-16hrs parked in sub-zero winds. If it pinches the pcm this t-stat mod can easily be adjusted or reversed.


Check out the following t-stat drilling 'artwork', extreme as it looks, it somehow works for that application.

http://dieselgiant.com/thermostatreplac ... dmodif.htm

[danthurs]

Never seen, or heard of a cracked head do to coolant suddenly cooling. And I live in very cold winters. -20 and lower is not unheard of. The only reason for a drilled stat is when the radiator is at the same level or lower then the engine. In our cars the top of the radiator is the highest point, this is where any air will collect. Keep the radiator full, and no problems. But if you want to drill it, feel free. But it's a total waste of time.

[bill buttermore]

The only reason for a drilled stat is when the radiator is at the same level or lower then the engine. In our cars the top of the radiator is the highest point, this is where any air will collect. Keep the radiator full, and no problems. But if you want to drill it, feel free. But it's a total waste of time.

This whole "purge air" idea is a local forum phenomena that doesnt have any basis in fact.

Based on my experiences with the L36 and L67, and based on reports from others here on the board over the years, I must disagree with you fellows. The next time you are working on one of these with coolant drained and the thermostat out, fill the engine at the thermostat opening up to the lip where the thermostat seals. Then, fill at the radiator and watch what happens at the thermostat opening. You will see and hear quite a bit of air air being expelled through the LIM. If you install a thermostat with no air bleed, and tighten down the goose neck, that air would be laying against the thermostat. The chamber that the thermostat sits in is pretty small, and it would not take a lot of air to keep coolant away from the thermostat's pellet.

I first observed this problem after working on a '97 L-67 and filling coolant at the radiator with a non-drilled thermostat in place. The car would not come to temperature (according to the gauge) but it was obvious that the top of the engine was getting warm. This was caused by a slug of air in the top of the LIM.

GM must have recognized a problem too, because I believe that newer 3800's are now fitted with thermostats with jiggle valve air bleeds.

I don't know what other factors might aggravate the problem for some or mitigate it for others, but I can assure you that the problem does exist, and that an air-bleed helps to rid the engine of trapped air.

[2003 SSEi]

My car came FACTORY with a drilled t-stat. 12 o'clock as referenced with you standing at the front of the car, the highest point in the LIM. My car has 0 issues with a drilled t-stat. Just drill a hole smaller than 1/8 of an inch, and you'll be fine. the amount of coolant it lets through is minimal, it's mainly for burping the system.

Wrong..... the little hole you see is not a "Drilled" stat. That is built in to every single Tstat produced. To Drill it you add another hole

[danthurs]

I've done several, and not seen this problem. The only car I ever worked on where it was a problem was a 84 Fiero, but that's a totally different set up. The radiator is lower then the engine. If you google drilled thermostat you will find most people saying it does little to nothing and is not worth the effort. But, as I said, anyone that wants to drill, feel free to do so.

[bill buttermore]

My car came FACTORY with a drilled t-stat. 12 o'clock as referenced with you standing at the front of the car, the highest point in the LIM. My car has 0 issues with a drilled t-stat. Just drill a hole smaller than 1/8 of an inch, and you'll be fine. the amount of coolant it lets through is minimal, it's mainly for burping the system.

Wrong..... the little hole you see is not a "Drilled" stat. That is built in to every single Tstat produced. To Drill it you add another hole

Again, I must disagree. Here is a photo of a thermostat from my '95 SLE showing the hole that I drilled in it. I can only find the hole I drilled. No others from the factory.

[harofreak00]

I agree with Bill. Here is a stock drilled stat.

[00Beast]

^ I'm guessing that was out of my 00?

[harofreak00]

Nope, thats from an L32. They didn't start using the factory drilled stat until 03 I'm guessing.

[bill buttermore]

I believe it is especially important for L36 owners to make sure air is not trapped in the LIM. That is because the coolant passages surrounding the plastic EGR passage in the UIM are fed from the highest point in the LIM. That means that if your L36 engine has trapped air, it is likely that those passages which otherwise would have been cooled to 200F or less, are now full of air and can rise to whatever temperatures the hot EGR pipe can induce.

I have often suspected that the reason some L36 UIMs fail more quickly than others may be that those engines have trapped air at the high point preventing coolant flow through the failure prone passages to the throttle body.

[SingsCountry1967]

To All: Please clarify what year/model or engine you are referring to when discussing such topics as design changes will make a difference. In some situations, two opposing views will in fact be correct depending upon the year/engine. With one exception, all posting so far has been very polite ... thank you and I expect the politeness to continue.

[bill buttermore]

I've heard mention of using RTV, GM RTV, and RTV copper. Could someone clarify which is better to use and where?

As long as you use sensor safe RTV (room temperature vulcanizing) silicone gasket sealant, you will be okay. Black is the most common. Copper is a little more $ but good for temperatures up to 700F, Gray cures up a little harder for joints where no gasket is used, like oil pans.

Application points for the RTV silicone for LIM change are described in the Techinfo article: Change UIM/LIM Gaskets

[GXP Venom]

I just dont see how when an engine develops water pressure from block heat how a small amount of air could keep that pressurized water away from the pellet long enough to cause damage. But I am not in any way knowledgeable in 3800's. Had a few and did regular maintenance. In search engines I can find no info in any other forums about this air lock relief so its seems odd to me is all. I have read several statements supporting what 93 SLE said. A drilled thermostat can kick out error codes on 2001+. But those applications were reported done for slightly lower operating temps.