Write-Up: Thermostat Installation

was just wondering do i need new gasket and o-ring? and also do you need to drain the entire system, or just enough to get it out of the upper hose?

Yes, replace both the gasket and o-ring. No need to drain the whole system. Be sure you bleed all the air out when you refill, with the bleed screw on the t-stat housing.

bleed screw? sorry im not too familiar with this.

There is an air bleed screw built into the top of the thermostat housing. I'd assume your 97 has it also? When you're all put back together and filled with coolant, you run the engine til it's warm enough for the thermostat to open, then crack open the screwa bit to let trapped air escape. Air in the system is not good.

ok thx for the tip

I had a leak after replacing my T STAT and found out that you do not need the gasket if you use the O RING.
I removed my gasket and the leak stopped completely.

EASHER wrote:

I had a leak after replacing my T STAT and found out that you do not need the gasket if you use the O RING.
I removed my gasket and the leak stopped completely.

I didn't want to take chances. I used the gasket w/ some rtv and no leaks.
Next time I will use the gasket again.... Come to think of it, Ive never not used a gasket

The gasket and o-ring combo was not used in all the model years from the factory. It IS listed for the later models for sure. I replaced both last year when I did my 180. No sealing issues. You need to completely remove the old gasket, probably requiring that you scrape it all off, I had to do quite a bit of scraping. If you don't have clean mating surfaces, you won't have a good seal.

I did see a few years of SI 3800s that had both, and I've seen quite a few 3800 thermostats that had only an O-ring and never leaked. I prefer the O-ring, much easier to change and no gasket scraping needed. I would only use one or the other.

deekster_caddy wrote:

I did see a few years of SI 3800s that had both, and I've seen quite a few 3800 thermostats that had only an O-ring and never leaked. I prefer the O-ring, much easier to change and no gasket scraping needed. I would only use one or the other.

lol i have both....

so should i get both or just an o ring or just a gasket?

I have them both, always have. No silicone used ever.

ok, and do i need to drain the coolant or not? chicken's writeup has me worried

Just use some paper towels to soak up the spill. It's enough lost coolant that you'll want to replace it, but not enough that you can't drive before refilling. Shouldn't need to drain coolant for a T-stat install.

like how much coolant are we talking?

maybe a pint or two? I've done it that way a few times too. It's really not that much coolant that spills out. A wide pan under the motor can catch most of it. Don't even take the upper hose off, leave it attached to the housing and it will all be fine...

so then i dont even need to get under the car.....that would make my day

No need to get under the car. A T-stat can be changed in about 1/2 hour with practice.

deekster_caddy wrote:

The ones I've taken apart with O-rings did NOT have a gasket OEM. It should only take one or the other.

Wow, I just found something I agree with Deekster on...

Seriously, for future viewers, here's my latest experience with a simple thermostat swap... First of all, I didn't realize how small these stats are! After only replacing V8 thermostats for the last 30 years, I can see how you'd want the "super-est" stat you could buy in here. 3.8 litres should have a bigger water outlet...

I just replaced the 195* stat on my supercharged '97 with a 180* Stant SuperStat. Everywhere I looked for the parts, I found both the flat gasket and the "O-Ring" listed. (Actually, it's really a ribbed and grooved trapezoid-ring... GM calls it the Thermostat Seal.)

My older brother, who's been a mechanic for 30+ years, told me that he'd seen this gasket "schizophrenia" in these applications before. He's seen both the O-ring alone and the O-Ring with the gasket, and he's replaced them with only the O-Ring...

Now, when I looked at the parts I bought, I admit that I liked the Fram gasket with the orange rubber rib running around the middle of the sealing surface, and my motor currently did have both the gasket and the rubber seal.

However, as I disassembled the water outlet, I found that the lower bolt (the one where gravity would lead coolant to) had rust on all the threads above the manifold suface. Also, there were stains on the side of the manifold below the water outlet... My brother and I believe that someone at GM was worried about the new O-Ring seal, and added a conventional gasket as insurance. But I think they bit themselves on the butt.

When they added the regular gasket, they didn't specify one where the inner circle was punched out large enough to go around the rubber seal... As such, instead of the O-Ring going "metal>rubber>metal", it goes "metal>rubber>paper>metal". It looks as though they created a cockeyed gasket 'crunch' that left a small path for coolant to weep out between the O-Ring, gasket, and the water outlet surface.

I used a proper, stiff, gasket-scraper to clean both surfaces (very important: the razor-blade types are too flexible, they can easily gouge the aluminum...I found a nice one with 3 different-sized blades in the handle for <$10.) After I had clean, smooth surfaces and had cleaned out the bore/groove where the O-ring resides, I installed the new stat with only the O-Ring and it has proven water-tight. Warning: With just the rubber seal in place, it is a very short transition between 'tightening' and 'tight', so go slowly...

I have one other, related, suggestion for parts: While working on the thermostat, it was virtually impossible to avoid wrecking the old, softened, "Supercharger Boost Control Solenoid Valve Air Filter"... Even with my local connections, this cheap little part was impossible to find without having to buy a whole bag of them.

My suggestion, which is very convenient when they have them in stock, is to buy the SuperStat, the O-Ring, the gasket (as a spare piece of insurance) and the filter, in one shipment from RockAuto.com... The convenience of getting everything including the filter delivered to you door is worth $16. However, I now say "when", because after I made my order, they called and said they didn't have any right now in the warehouse with the single filters. Now they sometimes add a line to the listing: "+ Sold in packs of 10; Price reflects cost of each individual item, not the pack"... Right now, that's $6.90 per box. The solenoid filter is at:
http://www.rockauto.com/catalog/x,carcode,1022050,parttype,5706

Finally, I'd point out that while it looks like a silly little part, this filter passes air every time you dip into the throttle. Whenever the throttle-body vacuum drops, the boost bypass valve actuator closes the bypass valve, giving you boost. When you let off the accelerator, it returns to the bypass position. Because the Boost-Control side of the bypass-valve vacuum-pot is "inhaling" and exhaling with every change in throttle-position when the Boost Control Solenoid is not activated, which is most of the time, that filter is preventing grit from entering both the boost control solenoid valve and the bypass valve actuator. As they both cost in excess of $50, an proper filter is a good expenditure to ensure their long-term health...


EDIT: I have since swapped the thermostat twice, to play with different temperatures. Properly cleaning the surfaces once, and using only the rubber seal with no paper gasket or goop, is definitely the way to go! The stat becomes a 5-minute quick-change job, and since you don't have to get in there with a scraper again, you don't wreck the BCS air filter... I did buy each stat its own seal, though, so I'm not immediately reassembling with the compressed one. Also, if you park the car nose-down, so the top of the radiator is at or below the level of the thermostat, you don't even lose enough coolant to warrant topping up.
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I don't recall any complications regarding this filter you mention?

When I did my 180 t-stat, the old had both the o-ring and the flag gasket in place. No signs of leakage. I cleaned things up and used a new o-ring and flat gasket with the 180, and still have no leakage to report, for over a year.

Quote :

When I did my 180 t-stat, the old had both the o-ring and the flag gasket in place. No signs of leakage. I cleaned things up and used a new o-ring and flat gasket with the 180, and still have no leakage to report, for over a year.

Same here. I've replaced my t-stat numerous times, last time being about 3 years ago. I always use both O-ring and paper gasket, never had a leakage issue.

Mine leaked like crazy without a gasket. Thats my input.

TonySmooth89 wrote:

Mine leaked like crazy without a gasket. Thats my input.

Did it have a good (new) O-ring and clean surfaces?

I just did my annual cooling system flush in the driveway.
I drain the coolant, remove thermostat, add a bottle of cleaner and fresh water, then let engine run for 15-20 minutes until up to temp. without thermostat installed.
Then drain and flush again with fresh water until I don't see any more orange from the Dexcool.
I had previously been using both the rubber seal and flat gasket for the thermostat, but this time i cleaned the old gasket off both surfaces and just used the "O-ring" seal, filled system with new coolant and distilled water(50/50 mix).
No leak from thermostat housing using just O-Ring.

Rickw wrote:

.... ..., filled system with new coolant and distilled water(50/50 mix). ...

Ive been sheltered alot... never heard of using distilled water in cooling systems. I ve always just used the waterhose. Why do you use distilled water?