77 chevy 350 thermostat replacement?


Well-Known Member
Ever since I got my 77 suburban I've never seen the gauge go past 1/4. Could be a bad gauge, or the previous owner removed the thermostat because they were lazy, or the thermostat is stuck open or some weird temp. I have a new 195f oem temp one ready to install, and the flat type gasket.

i was told i needed permatex thermostat goo so i have some of that. what do i do with it?? when installing the thermostat what is the best way to get air out of the system? i plan to not flush all coolant, just replace whatever spills out when i remove thermostat.

thank you for any information that will help me. i don't want to overheat my engine by trying to replace thermostat and doing it wrong, and i don't want it to leak afterward :'(

i found this video for the same type of truck. he did not use any goop or mention anything about getting air out of the system:

edit: and i think for the 99, instead of replacing thermostat myself, i'm just going to wait until my envoy is sold so i have some $$$ to buy intake gaskets and injection spider and have the shop do it then. since they have to drain coolant anyway.
Last edited:


New Member
Like the video shows, changing the thermostat is fairly simple. I would recommend draining the radiator, at least lower than the thermostat. I watched the video and I don't think he mentioned a recess cut into the intake manifold for the thermostat to sit. (also the direction the thermostat is installed, should be marked on the new one.)

You may not need the Permatex, providing the mating surfaces are clean! No old gasket, hard water deposits, corrosion... Clean and flat will help guard against any leaks.
Burping the air may take a little time. I usually park on a small hill. Remove rad cap, top radiator, start vehicle, top as needed. When the fluid starts to "expand", quickly put the radiator cap back on. Warm vehicle. when warmed up, shut it down and let it cool. When cold, refill, coolant tank also. Repeat as needed. Usually when I refill, I'll take it for a short run to check it out. Check fluid levels when cold


Well-Known Member
Another old thread... I almost bought the wrong gasket for my 1993 K code C1500. Rock listed various gaskets, both paper and the rubber O ring. Thankfully the service manual indicated one needs the O ring for the newer engines. Simple swap but I also suggest draining a bunch of coolant. Would have saved a pile of time.

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