[Sears]

Hi everyone, I've done several searches and a bit of reading as well as some troubleshooting but I can't seem to determine what is wrong with my 968. For background, it's a 92 coupe, 32k original miles, very original.

The Problem:
Heat works when it wants to, which isn't often. When I change the thermostat inside the car from cold to warm (blue to red) the temperature of the air flow from the vents in my car do not change. However, they might change some time later, could be 5 minutes later, not at all or 30 minutes of driving later. Erratic to say the least.

The Troubleshooting To Date:
The heater control valve (HCV) does it's job. I also had it replaced just 1 month ago (it was original, safety precaution) and I am certain of it's functionality as the engine temp drops in tandem with its opening. So that rules out a vacuum line issue at least as it relates to the HCV I believe, as it's responsive time and time again. I have also checked to make sure the clips are not broken and are working properly in the driver's foot well. I removed the cover and inspected the controls beneath, all in working order and connected.

So I'm not sure what to check out next. All of the vent controls work, A/C is incredibly cold (car was converted to 134a some time ago) and the blower works as it should. I look forward to your advice.
Thanks!

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[flash]

try bleeding the cooling system

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[Sears]

I should have mentioned I also had my coolant changed at the same time as when my HCV was replaced. The problem existed before and after the replacement. Could it still be the cause? Or other ideas?

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[flash]

well, since it's the hot coolant that supplies the heater with its heat, if it isn't getting there regularly because there is air trapped in there, you could have an intermittent problem - check to see that you have a real bleed screw (one with a hole in it) and that the fiber washer is beneath it - then bleed it with the engine fully warmed up and the heater on full hot

this will at least rule this out, and costs you nothing to do

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[apex]

Do you have access to the 944 factory manual? There is troubleshooting information there.

It's possible your interior temp sensor is not working. Stuck on warm might explain your ice-cold AC and never any heat.

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[Sears]

It appears I do not have the original bleed screw that has a hole in it (I presume in the middle of the bolt head, but I've never seen one) and a fiber washer. Mine is a standard-looking bolt with a metal washer of some sort. So I didn't screw around with bleeding it last night, but I did notice the coolant reservoir was a bit below the min level, so I added some distilled water to top it off (no coolant on hand). I do not think I have a leak, it is just a symptom of having the coolant changed a month ago. I may swing back by the shop that did it and have them bleed it again and install the proper bolt. Who knows when the original bleed screw/bolt disappeared, was probably a while ago.
Would my coolant being down just a small amount (probably only added 8-12 oz, maybe 16oz) cause the heater core to not fill when turned on? I know I could go out and drive the car and find out but it's raining so I left it in the garage today.

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[flash]

yeah - without the bleed screw, you'll never get all the air out - that is quite probably your problem

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[Sears]

Would it be as easy as ordering a new one? Is the replacement as easy as it looks? With a cold engine just take the old one out and screw the new one in? Then proceed with warming the car up, parking on an incline and bleeding?

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[flash]

yup - it's that easy

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[Sears]

Cool, thanks for the help! So the hole is visible without rotating the screw? I saw an old post that shows a picture of the front of the engine and the bleed screw shown on top of the housing is solid like mine, looks just like mine. Also, I noticed the coolant hose is just that, a hose (made of rubber) in that pic that goes to the top of the block to what I presume is the thermostat housing. My car has a pipe that fits into part of a rubber hose at both ends that is then clamped on. What is up with that? it sure looks like a proper pipe, it's the right size, etc.

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[flash]

no - you have to unscrew it to see the hole - it runs through the threads, perpendicular to the centerline - there is a hollow area along the centerline - this allows the air to escape up the hollow area and out the hole, while the threads provide a partial seal and prevent the fluid from passing

as for the pipe versus the hose, very early cars had the pipe - later cars had the hose

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[Sears]

Oh ok, I didn't back the screw off at all, I very well may have the hole. I wasn't sure if it was some fancier bolt than just having the hole run through the threads. I'll check that.

And thanks for the info on the pipe. Seems like that might actually last longer than a hose, no?

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[flash]

since i haven't seen a pipe wear out yet, and i have seen hoses wear out, i'd have to agree

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[Sears]

Nice! Guess Porsche changed simply b/c of cost? Interesting. I like that it is one less hose I have to worry about splitting wide open while driving.

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[flash]

yeah - that works

they did change a lot of things when they got off the first run - some were for expense - some were cosmetic - some were actually structural

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