Engine Coolant Temp Fluctuating

**webracin** · 12-11-2008

I figured out some valuable information and thought I would share it with you all.

Issue: Cooling temp constantly changing from around 210* to 180* and back to 210*. When at 210* there is no heat inside the car, but when it drops to 180* there is heat inside the car.

Solution: If you have worked on ANYTHING that requires messing with ANY part of the cooling system, you must bleed the air out of the cooling system using the bleed screw on top of the thermostat housing. Failure to do so will result in an air pocket forming in the top of the engine which can cause the thermostat not to open resulting in the car overheating. You can also have steam pressure in the top of the engine build up enough that coolant will not flow through the heater core inside the car causing you not to have heat in the cabin.

The car should be cool when adding fluid. Take off the radiator cap and top off the radiator, then start the car. Open the bleeder screw about 1 full turn. As soon as you see coolant dribble out, close the screw and top off the radiator again. Open the bleeder screw again about 1 full turn, close it when you get a steady stream of coolant coming out of the bleeder screw. Top off the radiator one more time and replace the cap.

Hope this helps you guys

webracin

**Zef_66** · 12-12-2008

I noticed this same exact thing happen in my car. But I noticed it when I had a water pump slowly leaking. As the coolant would get low, the temp would start to fluctuate more. So I knew it was time to add coolant.

**Sabrewings** · 12-12-2008

Any time I crack open the cooling system, I always bleed it. Good insurance and keeps the system air free.

**webracin** · 12-12-2008

Very true and I do as well, but when those damn plastic elbows crack on you and you lose some coolant its a little strange to see the temp guage go up....no heat....go down......HEAT....drove me nuts till I got home and found the leak.

webracin

**Bruteforce72** · 12-13-2008

i had the same thing happen to me low coolent light would come on but yet no puddles in the driveway till one day i noticed the temp going up and down and the heater blowing cold air like you said. One day coming out of the store i found a puddle under the car put it up on the lift and it looked like the wheep hole in the water pump leaking, we and got a new delco WP and stated tearing it down to find that damn elbo broke. Made me feel kinda good to finaly find out what the problem what for a while i had nightmears of coolent getting into the crankcase!

**Blown97** · 12-15-2008

Good info Web!!

**CSteen85** · 03-16-2010

Originally Posted by webracin

Very true and I do as well, but when those damn plastic elbows crack on you and you lose some coolant its a little strange to see the temp guage go up....no heat....go down......HEAT....drove me nuts till I got home and found the leak.

webracin

This is what is happening to me right now. If I am understanding this thread correctly, would replacing my upper and lower radiator hoses fix this problem?
My mechanic said I needed to have them replaced and I'm just wondering if this could be causing my heat inside the car to be going in and out and my temp gauge to be rising and falling a bit.

Is this right?

**RamairGTP2** · 03-19-2010

what he is talking about replacing are two plastic elbows,not the rubber hoses. If your upper and lower radiator hoses are not leaking,dry rotted ,or cut ...leave them be.

**NaturallySmashed** · 03-19-2010

Originally Posted by CSteen85

This is what is happening to me right now. If I am understanding this thread correctly, would replacing my upper and lower radiator hoses fix this problem?
My mechanic said I needed to have them replaced and I'm just wondering if this could be causing my heat inside the car to be going in and out and my temp gauge to be rising and falling a bit.

Is this right?

no, you probably have an air bubble in the system. webracin explained how to fix that. Take a pic of the hoses and post them, we'll tell you if they're good.

**GreyGhost** · 12-07-2010

Another way is to just run with the cap not tightened all the way closed. Just unscrew it that first 1/4 turn and it will vent the air out that way. Been done that way for years before any air valves were put in the system.

**matt5112** · 12-07-2010

the bleeder is still higher in the system.

**GreyGhost** · 12-07-2010

Originally Posted by matt5112

the bleeder is still higher in the system.

It is, but you have no guarantee that you have all the air out. With the cap cracked it will pressurize and push the air out without losing fluid. Just let it warm up until the thermo opens and let it cycle for a few minutes and it will push the air out and leave the fluid in.

**Taz Magister** · 01-02-2011

wait so you have to bleed that thing averytime you add or check coolant level?

**Bio248** · 01-04-2011

...did you let air in when you added coolant?

**brandon14597** · 01-26-2011

thank you for this info this is goig to save me some $$ i am going threw this right now the plastic elbow now is that down bye the (gooseneck) or down by the water pump

**cjmore** · 01-28-2011

Where is the bleeder screw on a 2001 GTP?

**gtpinsc** · 01-28-2011

on the thermostat housing... which is attached to teh right side of the lower intake mani.

**Lacboi** · 01-31-2011

drilled t stats ftmfw lol

**UCF04GPGTPCompG** · 08-02-2011

when bleeding the air out with the screw, are you supposed to leave the radiator cap off so the system doesn't gain pressure, or are you supposed to leave it on to help push that air out?

**Scottydoggs** · 08-02-2011

leave cap off, start car till its at operating temps, when the fan turns on you know the t state is open, unless you see the radiator level drop, if it does then re top it off, open the screw, let the air bubble out, till a stream of coolant comes out, shut screw, top off rad, cap it, done.