ClassJ

Hi Guys.

I am having a problem with my 85.5 where, at times, there is no heat at idle. If I bring the RPM's up at all, the heat starts working. There is also a gurgling sound in the dash like running water or air but the system seems bled. So far I have checked....

-All vacuum lines are checked or replaced for the HVAC system. Leak tested.

-Heater control valve arm moves when temp **** is turned to cool and is open when the car is calling for heat. Assuming there is no internal defect the valve seems ok but is original.

-Thermostat, water pump, etc etc a few years old, less than 5K miles.

-Bled cooling system using the usual procedure several times. Bleeding is always a PITA but never had this issue. Car seems ok. Not overheating. Went back and re-bled it after a drive.

I almost want to say that there is air in the cooling system getting trapped in the heater core and gets pushed through when rpms rise. But, I would think it would come out when the car is warmed up and we open the bleeder.

Do heater cores tend to clog in the 944's?

Any help would be appreciated.

Thanks

max_boost951

Try back-flushing your heater core. Remove your heater core hoses and use a garden hose with a spray nozzle, to push out gelled coolant. Spray through one hose and then reverse and spray through the other hose. Re-bleed coolant system.

-What happens is your water pump is driven by your timing belt, the higher the RPM the more coolant will go through your partially clogged heater core. At idle there is not enough RPM to move enough hot coolant through your heater core, so by the time the hot coolant reaches the outlet of the heater core the heat has been dissipated too much.

P.S. You can have a perfectly bled cooling system and still have poor heat!

ClassJ

So a quick update. I back flushed the block, radiator, core, crossover pipe, etc. Got some fine milky white stuff but nothing to write home about. Everything looks good as far as that's concerned. The heater valve is not restricted and closes on command when the AC is turned on.

I found a slight restriction in the tube running from the radiator left side up to the expansion tank. Now bubbles/water rush out of this port back into the tank when the car is running like I remember.

With all this said, the problem is still there. With the system completely bled, no heat at idle, give it gas, plenty of heat. A new symptom yesterday was that when the heat went away, the radiator also went cold, and the car started to creep up in temp to the top mark. The high fans kicked on at some point along the way here. I gave the car a little throttle, radiator hoses got hot, radiator got hot, car cooled off, plenty of heat.

Now suspecting one of two things, water pump slip, or thermostat sticking. Pulled the upper belt cover off. I felt I could turn the pump a little easier than what I remember. I re-tightened all the belts, checked the pump bearing feel. Put it back together. Same problem.

Hearing stories of water pump pulleys on rebuilt pumps slipping, I marked the nose of the pump to see if the pulley was slipping on the shaft. Nope. Same problem. This does not rule out impeller slip.

Last effort was to curse a bit and pull the stat. Only thing wrong and confusing is that the outer gasket was missing. No where to be found. Thermostat was rattling in the housing. Inner bypass gasket is fine. Pump in the car is the turbo upgrade pump with a 4.5mm thermostat spacing according to my notes from the belt/wp job. I am going to check all of the thermostat PN's etc.

I am essentially at a loss. Going to put a new stat in and try again. Otherwise, I think the pump is going to come out whether I like it or not.

Any help would be greatly appreciated!

Thanks