Why does it keep overheating?
 

Hi,

i have a 1992 SL SOHC over 150k miles.... i did a tune-up: plugs/wires, fuel filter, air filter, pcv valve & replaced the coolant. the damn thing is purring like a kitten...runs great. but now after the tune up, it overheats. it warms up slowly as ususal...then fan kicks on right when the temp gauge reaches 3/4 but it doesnt cool the engine down like it did before the tune up. it just keeps creeping into the red and overheats. After i refill the coolant and start the car i can see the coolant being sucked down into the engine (then i top it off) so i dont think the water pump is bad.

so far i've:
replaced thermostst
replaced coolant temp sensor
replaced coolant temp sending unit/sensor

what else could it be?

thanks

Sounds like an air-lock in the engine somewhere

are both top and bottom rad hoses getting hot?

may not be a water pump issue but maybe a partial clog of crap has lodged somewhere (???)

Or an air pocket as OA suggested though it sounds like you're burping it.....
Are you sure pressure cap on the reservoir is good/sealed tight?
Are you using a 50 50 mix? (sorry but someone had to ask)

Any stop-leak or equivalent nasty products ever added ?

I did notice that the top water hose is NOT getting hot. i replaced the water pump not long ago....i know it could be bad again but i checked it for leaks and the whistling noise it makes when going bad. all looks good. how do i check for blockages or air pockets? i've never added any kind of stop leak in the system.

the pressure cap is on there tight and i'm using a 50/50 coolant from Advanced Auto ...i'm NOT adding any water.

thanks for your help so far

Well, I'd pull the thermostat back out, and drop it in a pan of boiling water, to make sure it operates correctly. Assuming it does, make sure you reinstall it properly .....

Ocean Archer beat me to it, sounds like the thermostat is not opening.

in boiling water?
how exactly does that test it? what should i be looking for?

If the stat opens in boiling water, that means the stat is opening while it's in your engine. If the stat is opening that means it's not stuck shut. If it's not stuck shut then the stat is not the reason the car is overheating. Get it?

PS: If thats more then your able to understand you need to bring the car to someone that does.

of course i understand the WHY of the boiling water method...i've kept the car running on my own for over 17 yrs....what i meant was what do i look for/how do i know if the stat is working properly. not many ppl have seen a stat open/close in a pot of water. i was just wondering what to look for. but i imagine it will be obvious.

I imagine