Air compresses - water will not compress (at least at the pressures we are talking about). You definitely have air still in your cooling system if you see the level go down under pressure and then come back up when the pressure is released. Do you have the cap on when you have opened the bleeder valve? If not then the air just goes back into the system. Have you tried pressurizing the system and while it is under pressure very slowly open the bleeder valve? Also be sure the heat lever in the car is open all the way. I have an 84 and the heater is a mechanical lever if the newer cars use a solenoid to open up the heater core then that will cause all sorts of problems unless you can somehow force it open.

I hope this is of some help.

 

the problem with what you are saying is that pump pressuers the tank, the hose from the tank goes to the throttle body(via branch) then to the adapter on the pump. what happens there is that the lower hose and rad get pressured by it and the uper hose too...the pressure than takes the path of least resistance from the top hose to the bleedscrew...completely missing the heater core...I think it must be from the loose thermostat allowing the pressure to bypass the block and going straight into the rad....it must have to do with the seal on the stat...it must separate the radiator and block tightly in order for there to be two distinct cold paths for the coolant , allowing air to be pushed out by a pressure pump thru the heater core, the loose t stat is allowing the systems to bleed presure into each other so when pressured up, , water from the upperhose comes out when the bleed screw is opened, this is the path of least resistance for the water to come out and in the process, making a larger air pocket. that must be it! I am gonna replace the loose stat with a another one and make sure it is tight. Clint did you replace the stat on your car?

 

I didn't replace the themostat because I didn't think it was the problem. From my understanding if the t-stat failed the coolant wouldn't drop and thus the coolant in the expansion tank would not heat up.
My problem has become contunually worse as the days went by. For a while I could drive the car around and all would be well except no heat. The coolant level would be normal. Then if I kept the RPM's high, the heat would work and the car would overheat. I would check the coolant level again and it would be down.
Now...Whenever I drive, I have no heat and it overheats everytime. It will go all the way up to the red mark and stay there...never over...just TO the red mark. If I get a little aggressive with the car, the temp will drop rather quickly and then go right back up. I can hear the heater core bubbling so I know there is air in there. The system holds pressure so I am thinking maybe the shaft on the waterpump snapped and worked for a little while and now maybe it is worn. Or maybe the impellers are just not pushing enough coolant?
What I'd like is to know how to test the waterpump while in the car. The hoses do "pump" up but I'd like to know how I could measure the flow rate. I am really leaning towards inadequate flow and that's was causing the air to remain in the system and the overheating.

Thanks!

 

Nick, I agree with you about the throttle body coolant lines...they SUCK! I think I am going to cap them since I live in the south.... I don't need my throttle body warmed!

Maybe then it will be easier to bleed the air out.

 

Bump anyone...

Do you think the waterpump could be bad? Worth replacing or should I concentrate on another direction?

Thanks..

 

I have this same problem with air and overheating. I think it is unlikely to be a water pump (but don't quote me). For the longest time, I thought it was a head gasket. It is hard to test for exhaust in the coolant because of the position of the filler cap to the rest of the engine. I had to pressurize my coolant system and the coolant dropped nearly half the tank. That confirmed the air. I changed all hoses and clamps. So far, I still have air in the system. I am considering using a vacuum machine to help fill my coolant. Another option I thought was to add a release valve in the rear right after the heater control valve.

 

Have you done a leakdown cylinder test?
That was the answer to my problem, my headgasket was leaking between cylinders 2 and 3. A small enough leak to prevent mixing, but enough to pump air into the cooling system. I am actually in the middle of replacing the headgasket.
Good luck!

 

did anyone ever mention that when you bleed it, and the coolant drops real low, that you have to ADD more coolant? Not sure anyone said that but you do. If it drops and you dont add coolant, youll just have steam forever....the system needs to be all coolant, your trying to bleed the air out to replace it with coolant.

 

Going to do the leakdown test in the next day or two. Do I need 185 PSI or can it be done with less air pressure?

 

One question I have, with all the challenges bleeding the system with a thermostat and air. Why not drilll a small hole in the thermostat as the track guys do so you can never over heat due to a stuck valve. This would force the air to the vent hole and eliminate all the issues. Porsche race tech helped me with my track car and this was his advise.

 

Jim -
Works good when you are in warm climates, but in the winter the small amount of bypass prevents it from building enough heat to keep you warm.

Good to hear you figured it out Clint!