Overheating issue...

[CountyLineGarage]

I’ve got a 95 Sierra I just replaced manifold gaskets on. I also replaced the thermostat just cause they’re cheap and why not... I bled the system of air a few times though I’m confident the first time worked as no air came out after that I just wanted to be sure. But, (there’s always a but) for whatever reason after initial start up say in the morning or after work it wants to overheat once getting up to temperature and shooting way past into the ”check gauges” territory. So I shut it off and pull over wait a few minutes maybe a bit less and start it up again and bam instantly shoots back to below 210. (It’s a 195 thermostat). Any suggestions. Don’t think it’s a head gasket as it’s a pretty fresh rebuild.

 

[Schurkey]

Defective "new" thermostat, sticking shut then popping open?

 

[CountyLineGarage]

I don’t think it’s a defective thermostat because after the first heat up it doesn’t do it anymore but occasionally gets a bit above 210

 

[Frank Enstein]

Get a BRA-330-195 from Summit Racing. It is pressure balanced to prevent that from happening.

 

[PlayingWithTBI]

Get a BRA-330-195 from Summit Racing. It is pressure balanced to prevent that from happening.

I have one of those in my 5.7L it does lag a little opening but doesn't go that high. It'll hit about 212* (on the gauge) then drop down to ~208* operating temp. My ECM only sees ~197* opening and then 194* operating. Not only is the gauge questionable but, it's reading between 2 cylinders in the head, not the water jacket.

 

[Schurkey]

Get a BRA-330-195 from Summit Racing. It is pressure balanced to prevent that from happening.

Ehhhh...That's essentially what I put in my Toronado. Did exactly as the OP described--overheated from cold, popped open, good for the rest of the drive.

"Pressure balanced" doesn't mean it can't be defective.

 

[RichLo]

try a radiator cap

 

[CountyLineGarage]

try a radiator cap

Did one of those a couple months ago don’t really think it’s that either unfortunately. Just kind of praying it’s not some sort of head gasket issue.

 

[Erin]

I have one of those in my 5.7L it does lag a little opening but doesn't go that high. It'll hit about 212* (on the gauge) then drop down to ~208* operating temp. My ECM only sees ~197* opening and then 194* operating. Not only is the gauge questionable but, it's reading between 2 cylinders in the head, not the water jacket.

Same here. When first reaching operating temperature it will shoot up past 210, for about 2-3 seconds, then drop back to operating temperature and stay there. It's a 195 thermostat.

 

[1997]

Did one of those a couple months ago don’t really think it’s that either unfortunately. Just kind of praying it’s not some sort of head gasket issue.

Did you figure it out, my 95 just started doing the same thing.