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Join Date: Dec 2008
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924 turbo overheating?

hi, all, ive just bought a 1980 924 turbo, it has been parked for 20 years!, car was indoor and is in great condition, 56000miles from new. ill done some of the work needed to get her back on the road, engine flush, new leads, cap, thermo, coolant. have not driven yet as clutch slave is leaking, new one ordered.i m a big porsche man, i drive a 928 s4 daily and have 2 911 sc's, but this is my first 924 and i love it so far. problem i have is, when i first got her going she overheated right away, so flush her out and changed thermo and put coolant in, it does not go to red now, but goes to middle then creeps up to 3/4, fan kicks in and goes back down to middle, it heats up quicker with heating inside car off, is this normal? and im a little worried when i drive her it will overheat, ive heard there is a problem with 924s and 944s overheating, any advice would be great, cheers thomas

Old 12-06-2009, 03:56 PM
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If you arent driving, then eventually the temp will climb to about 3/4 mark, and fans will cool it down. I think this is pretty normal, and wouldnt worry. What does your temp on your 928 do if you let it idle. Doesnt your fans kick on around the 3/4 mark?
Old 12-06-2009, 09:02 PM
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Don't start it again until you have replaced the timing belt.
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» 1980 931 - Got boost? ♦ 1987 924S - Pro44 ♦ 1987 924S - Junkyard score «

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Old 12-07-2009, 11:12 AM
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^+1. You don't want to end up with bent valves. The timing belt is typically less than $30-$40 in parts, and easily doable by the home mechanic, typically in 2 hours or less. Change the timing belt tensioning roller while you're at it.

To answer your overheating question, there are a number of things that can contribute to hot running of the 931. You need to make sure both fans are cycling on correctly. The quick and dirty way to check this is to start the car, and then turn the AC on. This should force both rad fans to kick in. If not, then you have to figure out what's wrong. It could be a defective fan, defective wiring in the fan circuit, a defective fan relay (actually on the A/C circuit), or a bad fan switch (the big one near the upper rad hose in the rad itself).

Change your thermostat. Cheap and easy to do, no reason to leave it to chance that you have a stuck or ready-to-fail thermostat. Consider replacing it and the fan switch at the same time, and make sure you get them as a temperature-matched pair.

You should also consider a thorough flushing of all the old coolant, a proper mixture of glycol and water, add water wetter (if you can get it Ireland), and properly bleed the system. If the system currently has air in it due to improper bleeding (either by you or the previous owner), the car will more easily overheat. Normally, I would suggest also replacing the coolant expansion cap, but the 1980 931 cap is a screw on type, and not replaceable with the off-the-shelf twist lock style. You can easily replace the coolant expansion tank with a 944 style fender mount unit, and those will take a standard expansion cap.

Running improper oil also contributes to heat gain in the engine compartment. The owner's manual calls for 15W50 or 20W50, which should be suitable during the warm season. Not sure how could it gets on the emerald isle, but you might want to consider 10W40 during the cold season.

Other less likely culprits could be clogged heater hoses or clogged radiator. You might also consider performing a pressure test on the system to verify that you don't have a pin-hole or slow leak somewhere. While you're changing the timing belt, you should spin the water pump to see if you hear any noticable noise from its bearings. If so, replace it forthwith. Cheap and easy to do, particularly once you've started on the timing belt. Another contributor to heat could be late timing or lean mixture, but I wouldn't start chasing that down until you've thoroughly gone through the cooling system itself.

For point of comparison, the two 931's that I have on the road don't run any hotter than my normally aspirated 924, even after hard driving (although I've not tracked any of them). Normal operating range on my cars is at the first tick mark about 80% of the time. During the hottest part of the summer, the needle will sometimes approach 12:00 on the temp gauge, but it never gets past that before the fan kicks in. All three of these cars have been thoroughly gone over, all preventive maintenance done, and in good tune.
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Old 12-07-2009, 11:27 AM
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+1 to changing the timing belt and all the above.

My 82 has a cool thermostat, but hot fan switch. They're available in different flavours. The t-stat will keep the engine running at the first (white) mark in warm weather - either while cruising, at up to 70mph, or idling. However after I come off the highway, the heat will build up and need to be dispersed by the fans - in other words, it won't stay at the first 1/4 mark anymore without fans.

The fans however don't kick on by themselves until the 3/4 mark, same as yours. Then it'll pull the temp down to about the middle mark before they shut off. I would probably be better off with a cooler fan switch, to run the fans around the middle mark.

Note that I have two fans, not one, as I have AC.

If I run the AC, which runs the fans constantly, the temp never gets above the middle mark, usually only sits at the first mark.

Also note: a properly functioning cooling system in a turbo will not overheat. Period.

2nd note: the 924S and 944 have a completely different engine etc than the 924 and 924 Turbo. They shouldn't overheat either.

You might be better off with a cooler thermostat - what are the markings on yours?

Though, overall, it doesn't sound too too bad... just a question of how quickly the temps come up. My turbo does heat up quickly when driving, even in the cold weather. Much nicer than an NA!

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Old 12-09-2009, 05:12 AM
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