Thermostat. Gasket or O-ring, or both?

[rob249]

Shortly after i bought my 94' Yukon, the thermostat began sticking. When i bought the parts, they gave me a gasket and an o-ring, which what was on the truck. I replaced it, everything seemed to be fine, until I idle for more than 10 mins or so, then the temp will rise slowly, stabilizing around 220. I can run the throttle up 1000 rpms and the temp will rapidly drop back to 195. I do also lose a very tiny amount of coolant over a long period of time(maybe a quart every year). No heating issues at all above 1000 rpm or so, even while towing.

To me, this all means that i'm leaking pressure, probably at the thermostat because it cannot seal with both the o-ring and the gasket? Does this make sense?

New radiator and hoses had no effect.

 

[454cid]

I believe the V6 installed in other vehicles used both, but our truck v8s I believe are one or the other. My 454 uses just the rubber o-ring.

 

[evilunclegrimace]

It is one or the other,not both.

 

[rob249]

Well certainly it is one or the other, but which?

 

[smdk2500]

Does the thermostat sit inside the groove on the intake with the oring installed or does it sit on top of it? If it sits on top take the oring off and use the gasket. If it sits in the groove throw away the gasket.

 

[rob249]

Perfect, it does have a groove, O-ring it is. Thanks all

 

[454cid]

Perfect, it does have a groove, O-ring it is. Thanks all

The o-ring style is so much easier to change.....no scraping a stuck gasket.

 

[Schurkey]

Does the thermostat sit inside the groove on the intake with the oring installed or does it sit on top of it? If it sits on top take the oring off and use the gasket. If it sits in the groove throw away the gasket.

Perfect, it does have a groove, O-ring it is. Thanks all

Define "groove".

Every Chevy V8 thermostat area since before I was born has a groove machined into the manifold that the thermostat sits in.

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[smdk2500]

Define "groove".

Every Chevy V8 thermostat area since before I was born has a groove machined into the manifold that the thermostat sits in.

I apologize I should have explained better. On the later manifolds up to at least 95 the groove is slightly bigger to accept the o ring. My 95 with the 5.7 used a oring for the t-stat seal. I don't remember what my 94 with a 5.7 used. When I replaced the intake gaskets on my 95 I broke the quick disconnect off in it and damaged the threads trying to get the broken piece out. I had a intake off a 90 f-body that was tbi and I had to use the paper gasket because the t-stat from the truck would not fit because of the oring. It was physically to big with the oring. It sat on top of the t-stat hole. Once I removed the oring it fit like it should.

 

[Dropped88]

Here's the o ring style

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