96 Lumina over heating not sure y!!!!

I have a chevy Lumina 3.1 that keeps oner heating!I have changed the water pump,changed the therm,changed the intake gaskets!not sure what else to do the coolant is stayin in the overflow!!!!over heats sometimes abd goes back down but other times it stays up!

You've either got trapped air from not bleeding the system fully, or compression in the jacket from a cracked head, head gasket, warp, etc.

Open the radiator, open the bleeder screws. Fill until coolant comes out of the bleeders. Close them, start it and warm it up for about 10 minutes. Then shut it off and repeat the above. Keep doing this until no air bubbles are seen at the bleeders when you open them.

is your radiator restricted?

When I am sitting and just idelingit doesn't over heat .it only does when u r driveing ,but u can floor it and the temp goes back down !I am thinkin their is a blockage somewhere,just not sure where or how to go about finding it !

had an 85 monte SS did the same even after all u did....was a bad thermostat even tho new...test it in a pot of water 1st... good luck

When I am sitting and just idelingit doesn't over heat .it only does when u r driveing ,but u can floor it and the temp goes back down !I am thinkin their is a blockage somewhere,just not sure where or how to go about finding it !

That is textbook trapped air behavior....

I tested the thermonstat that I took out it only opens about 1/2 an inch not sure how much it is supposed to open! I can't seem to get all the air out

What is the best way to bleed all the air out of this? We have been trying to get it all bleed but it seems like it is near impossible to get the upper hose to retain coolant...just seems to trap air, but everytime we try to bleed it out it just seems like more air enters and we seem to be getting nowhere. Any help is greatly appreciated.

Mike

those are a pain. if youve already done it by opening the bleeder and letting as much air come outta there as you can. then the way ive done it, and it seems to work really well is start it up and let it get warm. rev it to about 2000rpms and when it starts to get hot let off and let the rpms drop to about 1500 and rev it up to 2500 and drop it back to 1500 rev it to 2500 and repeat, do this until the temp drops down fairly well. after that happens check the overflow and fill it to the proper level and start all over again till you dont have any problems. you basically have to surge the air out and it is a pain in the arse. ive had some that took 10 mins and some that took 30+ so good luck :)

If it keeps developing large amounts of air each time you start the motor, you may be blowing compression into the cooling jacket.

If the upper hose gets hard as a rock within a minute or so of staritng up cold, there's little doubt...

the other fun test is to start it without a radiator cap (if there is one on the radiator its a lot more fun). usually if the head gasket is blown bad enough itll force water out of the cap or bubble really bad. 3.8L fords are bad about head gaskets and its great to get the new guy at the shop with that one :) he gets all leaned over the cap looking for bubbles when you start it and FWOOSH he gets doused with water.