HOT-SHU (a.k.a. Wes Shew)

1st time I've seen this on my 91 S2. Gauge was slowly rising to 2nd hash mark (100 deg.C) so I pulled into the gas stn. With engine running the fans are on but the air drawn thru is cold. Water pump belt is turning. Coolant level is fine. Wires to rad thermoswitch still attached. Attempted to remove coolant tank cap and hot coolant started pressurizing out. What should I test next? Bad gauge? Bad sender? How do I test them?

Drove home with heater on full hot and interior fan on high. It got super roasty hot inside the car, even with the windows down. Gauge needle dropped some then went back up, it also jumped up & down a bit a couple times.

With needle above 1st hash mark (80 deg C.) and then turning engine off, the fans are off (normally would stay on until coolant temp is below 1st hash mark).

What's goin on guys?

I may have a spare thermofan switch.
TIA

Waterguy

Sounds like the coolant is not circulating through the radiator. This is usually caused by a bad thrmostat (failed in closed position.) Try replacing the thermostat (a cheap but difficult task.)

Once you have the thermostat out you can test it by heating it in a pot of water. Should open at about 80 C iirc.

'88-924S

WAIT!!! I had similar problem, check your grounds. A jumping needle is a sign of this. Check archives for "grounds" and you'll find all of them. Some are a pain to replace, but it immediately solved my problem, also it's a much cheaper and easier way to start! I think someone here has a kit of some sort, maybe Iceshark? Good luck and post what you find out.

DLarsen

My 86 944 n/a with 250,000+ miles had a similar condition about a year ago. Driving home from work (about a 40 minute comute), my temp gauge needle begin a slow steady climb into the "danger zone". I pulled the car over, checked under the hood. Fans weren't on. Didn't know if the fans weren't working or what. So I called for a tow and had the Porsche dealer look at it. Turned out to be a faulty temp sender. Temp sender was original. My first "breakdown" on the road requiring a tow.

Blue S2

Mine car sometimes in traffic starts climbing to the red, but never makes it, the fans engage about 1/8" inch or so before red and bring it back down. It cycles like that sometimes. Everything checked out fine though. Is this similar to what you are having?

HOT-SHU (a.k.a. Wes Shew)

Tony, no that's not the symptons mine is showing. Altho what you described is not normal either. I'm thinking failed thermostat too, has 60k miles on it if not more. I'm gonna use my tire temp pyrometer to measure in/out rad temps. If it is the thermostat, I guess might as well replace belts and waterpump too? Ouch, open wallet!

Blue S2

Does anyone know anything about mine symptom them? My mechanic and i went over everything and couldnt find a thing. All parts are good. Fan switches are all new, etc... I never get to red, i just cycle between normal and a hotter if i get stuck in traffic or im chugging along slowly at like 20 or 30mph.

led

Tony, is your system properly bled?

HOT-SHU, just out of curiosity, are the fans pulling air front to back or the other way around?

Blue S2

Yup! It did it before i changed my coolant tank, and afterwards. I am going to give everything a good check-over in the spring when it comes back out. Everything else seems fine. All my parts are good, ive within the year replaced the head seals, etc... It only does in if i am very slowly moving, or stuck somewhere. Once i get to 30mph + it disappears and stays cool.

HOT-SHU (a.k.a. Wes Shew)

Well I did'nt change anything so there's no reason for fan direction to change. But in any case I feel air bein blown onto my hand towards the engine.

Tony, can you duplicate the overheating while parked/stopped and check to see if the fans are on after the 1st hash (around 90deg C) mark?

Peckster

Probably a bad rad. Not efficient anymore.

Blue S2

The fans and radiator work perfectly! My mechanic tested the whole system over 3 days for this specific occurence. Letting it run for a while and monitoring its actions. Nothing has led to a malfuntion of a part yet. We could replicate it a million times. It just starts getting warmer, goes up and then comes back down, goes up and comes back down. Any ideas?

Sorry to hijack the thread! I guess this might be something similar though?

HOT-SHU (a.k.a. Wes Shew)

Well just came back from the garage. While parked I got her all warmed up and the temp gauge got as high as just before the 2nd hash mark, say 97 deg C. Measured pyrometer temps of coolant pipe coming out the head, maxed at 95 deg C. and into the block at 85 deg. C. So i wonder if the thermostat is not opening 100%.

Bled for air to be sure, and no change. Idling for close to an hour it never did go into the red or vent at the cap. Fan comes on at normal temp, say around 92 deg C on the gauge. But it never brought the temps down enough to shutoff. Turned the interior heater on high and the temp came down to the first hash and fans shutoff. Turned heater off and temp rose again and fans kick in normally. But again temp never came down enough for fan to shutoff.

Surprisingly when the engine was shutoff, the fans did'nt continue to run. Huhh?

What should I check next?

HOT-SHU (a.k.a. Wes Shew)

where is the gauge temp sender?

led

If the rad is dirty or has a few lines clogged it will be less efficient like peckster suggested. I don't think there's any other way to tell if it's clogged other than opening the rad. Mine was clogged when I first got the car. After a nice and expensive cleaning it now works fine...


HOT-SHU, if I were you I'd start with the easiest and then move on. So first grounds, then the temp switch then thermostat.

Edit: I guess grounds and temp switch are scratched then...
IIRC, the temp sender is underneath the throttle body next to the temp sender for the DME, cant recall which is which though.