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chrisvs · Joined: 26 Jun 2012 Posts: 25 Location: North Bay, Ontario

I did a thermostat change on my 924 NA this weekend, to try and cure a high temp reading that I have been getting. After snapping both bolts in the thermostat housing, and then spending 5 hours drilling out what was left of the screws, I replaced the thermostat, bled the system and did some testing..... the results seem to be a bit better than before, but temps still show high, especiall in stop and go traffic, or after shutting off the car for a few minutes, then starting it back up. I am not 100% convinced though that I am having an overheat problem...

When I park the car after the temperature shows "hot", as in, just into the red zone, the fan runs for maybe 2-5 minutes, then shuts off. I can find no sign of coolant boiling over at the overflow either. The gauge bounces wildly until the car heats up, so I am suspecting either the sender is shot, or a bad/dirty connection or ground. Do you think that I am headed in the right direction with my troubleshooting?
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1978 924 4-spd

Grenadiers · Posted: Mon Jul 23, 2012 11:03 pm Post subject:

Could be a bad ground. My fuel gauge is erratic on my '81 car, and after swapping to a known 'good' gauge, it still does it. Affects my oil pressure gauge as well, which can cause sleepless nights!
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emoore924 · Joined: 13 Apr 2004 Posts: 2822

My initial thought was bad ground too. But I'd also check that the connector on the sensor is on tight (back of the head) and that the fan switch is working and properly matched to the t-stat.

flosho · Posted: Tue Jul 24, 2012 4:33 am Post subject:

Have you tried to bleed the system? Could just be air trapped in the system causing it to run hot.
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B · Joined: 25 Apr 2006 Posts: 487 Location: Ohio

I just finished fighting an overheating issue as well and this may seem like overkill but this is what I went through and so far so good. This was after changing the thermostat and radiator cap.

flushed system heater valve open and on full. Heated it up with water. Let it cool.
Emptied. Filled with 50/50. Heated up. checked hoses and radiator to make sure heat was moving through the system and fans were coming on correctly - used a meat thermometer in bleed hole to check temperature for fans and used that as a gauge for marks on dash gauge.
Let it cool. Started it and let it run for 20 minutes while bleeding the system.

I also rechecked connections, timing and exhaust manifold bolts.

lot of stuff but all in all temperatures are much better.

hope this helps
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1979 924 n/a
BAE turbo
5-speed snailshell

!tom · Posted: Tue Jul 24, 2012 12:13 pm Post subject:

Sounds like you've still got air in the system. Try filling it through the bleeder.
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78 924 NA
5-lug

chrisvs · Joined: 26 Jun 2012 Posts: 25 Location: North Bay, Ontario

Thanks gents for all the ideas.

When I changed the stat, I did burp the system for a good 20 minutes, inlcuding elevating the front end slightly and backfilling through the bleeder. I think I will end up emptying the system and back flushing the rad, just to be on the safe side.

This will be done as well as checking and cleaning the sender and gauge connections. Barring that, water pump, bad sender or bad gauge are the only things I can think of.
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1978 924 4-spd

Paul · Posted: Wed Jul 25, 2012 11:52 am Post subject:

One way to eliminate the grounding question is to run a wire from the engine block to the ground point on the temp gauge.
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patand · Joined: 12 Jan 2007 Posts: 91 Location: Sweden

I recently had a similar thing going on with my temp gauge.

For me the problem was the connection on the back of the instrument it self. I removed the instrument and cleaned the connection on it and after that it worked fine.

Also recently changed the ground wiring from the battery to the chassies on my car and that made all the intruments much more stable. So ground issues can affect a lot and I would not be surprised if that is the root cause to your problem to.

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Gene · Posted: Fri Jul 27, 2012 1:59 am Post subject:

Another test that will verify that you have a grounding problem is when you have a high reading on lets say your temp gauge when the car is running, shut off the engine and turn the ign. back on and if you get a normal reading on your gauge than check your grounds. I put on an additional ground from the engine to my chassie and now all gauges work normal.

chrisvs · Joined: 26 Jun 2012 Posts: 25 Location: North Bay, Ontario

Well, I might have another lead on the high temp problem.

The car was back in at my mechaninc's shop for rear brake work (parts finaly came in) and, while driving it back into the shop he noticed how poorly it ran when cold. He went searching for vacum leaks, and he happened to shine his light under the timing belt cover from the back side, and he noticed a whole string of missing teeth! So, a new timing belt has gone in. Maybe the timing had shifted slightly, causing a lean burn? I guess I will find out after I drive it home..... wish me luck!
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1978 924 4-spd