[DaveN]

So my son is driving down the road at 80K (50 to the south) and all of a sudden the coolant dumps on the road. He pulled over and parked luckily. I went to visit the car just now and there is almost no coolant inside the engine bay, all the hoses look great but the coolant tank is empty. I refilled it and bled the system and revved it a fair amount. The temp is stable at 9:00 and nary a leak in sight. I bought a new rad cap thinking it may have failed and dumped out the overflow but all I ever read here is that if it fails it will leak on cool down. Any wild guesses BESIDES HEAD GASKET? That is slated for this winter before the SC, well that was my plan anyway [img]style_emoticons/<#EMO_DIR#>/sad.gif[/img]

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[banditsc]

Heater Control Valve?

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[968rz]

T-stat stuck then released after cool down, I'd replace it JIC.

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[DaveN]

HCV was where I sent first! All good. I picked up a new thermo cap but they don't have any rated as high as 1.50 BAR (22 PSI) so I am hesitant to use the 16 PSI one they had. At least that's what is stamped on my current one "150".

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[968Syncro]

Well, I've had the plastic radiator drain plug fail, the lower hose get a hole from the power steering belt rubbing it, and the HCV. But all of these were hard failures in that they leaked upon refill. Not sure what type of leak could be intermittent, i.e. can't be seen after a refill. Your suspicion of the pressure cap sure seems like a good candidate.

Roland

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[DaveN]

Update. Just got the car home before the temp went past the 2nd marker. Parked the car and there was a suspicious silence-no rad fans!
Both fuses are good so is this the infamous resistor pack?

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[flash]

there is a diagnostic guide for the cooling system

http://www.968forums.com/index.php?showtopic=9029

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[rl968]

Probably a dump question, but you never know...Is the fan plugged in? When the previous owner replaced the radiator in my car, he forgot to plug the fan back in, it overheated, luckily no damage.

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[DaveN]

I had a new rad about 2.5 years ago all was great until Monday. I have a new fan temp switch on order, looks like the old one doesn't click in at 92 deg. They appear to be wired in series so if there is no 92 contact there is definitly no 102 degree fan as well so things get hot fast. I wish the guys who did the rad replaced the cooling switch at the same time but it looks to be original.

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[DaveN]

Maybe I have more issues [img]style_emoticons/<#EMO_DIR#>/sad.gif[/img]
I put in the new fan temp switch and spent the next 2 hours trying to get the fans to come on. No matter what the engine temp the switches would never close. I figured there was air around the switch still so I bled the system many times but it seems there is always air (steam) coming out of the bleed hole and it's never ending. I can rev the engine without a problem - runs smooth, no water in the oil or vapour out the exhaust.
I got the fans to finally come on but at very high temps. It's almost like the water pump isn't circulating water and therefore the rad stays cooler than the top of the engine and thus boils at the bleed valve.
The rad does get hot after the car warms up but maybe that's just convection?

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[flash]

i just had what i thought was a similar problem - it looks like in my case it is the gauge now reading wrong - real measurements showed that i was much cooler

in your case though, i tend to suspect the resistors, which are located on the firewall, at the passenger side, right behind the vacuum canister thingy

there is a cooling system test DIY here on the site (note the link above in post #7) that explains how to check

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[DaveN]

Thanks. I have been to section 7 of the cooling doc and got stumped last night by the odd behavior of the bleeding. Will continue on the next section to try to determine what else is funky.

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[flash]

make sure you have a bleed screw, and not just a bolt

make sure there is a sealing washer underneath the bleed screw

make sure the heater is set to high temp, and the fan is on

make sure the coolant is up to thermostat temp before bleeding

make sure the radiator cap is on and tight

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[DaveN]

Bad news. Me thinks the water pump is in heaven, or hell the way I feel about it now.
Talked to my mechanic today. Seems to water pump outlet is into the bottom and out the top. My rad gets hot at the top (convection) and is cool at the bottom after the thermostat opens. That means no flow plus I checked and with the heater on high I get almost no heat, sigh.
I have searched for a water pump DIY but haven't found it yet. PLus the reman, OEM decision. I bought a new Laso for my 944 once and it lasted a month so Jacks a little scared, redrum, redrum. Even though you guys have favourable experiences with reman I am feeling drawn to OEM.
Suggestions?

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[flash]

ugh! that sucks

the bummer about the pump is that you have to yank the belts to do the job

the cool thing about the pump is that you get to change the belts to do the job

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[Cloud9...68]

Before you yank the water pump, are you absolutely sure your thermostat is opening? A thermostat that's failing to open all the way is an alternative (and much less expensive and painful!) cause of lack of coolant flow. Unfortunately, this isn't an easy thing to check, and pulling the t-stat is a very messy (though pretty easy) job. However, I don't see how a malfunctioning thermostat can cause your fans to not turn on... The cooling systems on these cars are very tricky, unfortunately.

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[flash]

if the water in the radiator never gets hot, then the fan switch would never see the temp needed to turn on the fans

so, a bad thermostat could do what he is seeing

i agree that pulling that out first makes sense - it would have to come out anyway, and it's not all that hard (other than the stupid clip design)

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[DaveN]

Yea I'm sure it opens as I can feel the convective water flow as the engine reaches temp. As per my mechanic I removed the bleed screw and looked in there while the engine was warming up to watch the coolant. Coolant never moved [img]style_emoticons/<#EMO_DIR#>/sad.gif[/img]
I miss the old days when a water pump went bad over 6 months and you knew it because of the racket it made.

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[banditsc]

At least it failed the way it did, the alternative would have been a lot worse...

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[flash]

alrighty then - since you are going to be in there, this is the time to get everything on the front end handled

check the balance shaft seaks for leakage
boil out the radiator
new radiator hoses
put in the low temp fan switch
drill the new thermostat
new gates belts and new rollers

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