We recently got an email from a reader in the United Kingdom with a 1988 924S who is having overheating issues. Alan Bradshaw, the chairman of The Porsche 924 Owners Club in the UK has become a friend and resource, as are the members of this great club. The 924 is very popular in that part of the world, and as a member I get to participate in their activities, albeit from a distance across the pond. Alan has been dealing with a problem for a while, and he reached out to us to try to figure out what to do next. It’s an all-to-familiar story – “We’ve tried everything, and nothing is fixing the problem.”
Alan has had the car for about two years, and upon purchase he thinks the the temperature was normal. They fitted new belts, water pump, thermostat, and the other things that are normally done on a new purchase like this. From then the car seemed to run at the three-quarters mark on the gauge and goes up into the red when stopped and idling. And yes, the fans turn on when they are supposed to.
Next came a brand-new radiator from Porsche, another water pump and thermostat, a new radiator fan switch, with no real significant difference. A refill and bleed with Classic Cool waterless coolant, even bleeding with the front end raised up, and no difference.
Finally he fitted a dual fan setup on the radiator. That did seem to help somewhat, but this is a common issue within the club.
Our suggestions were probably not that helpful, but it does point out a situation that we all face now and again – nothing we do fixes the problem. Everything that Alan did made sense, especially replacing the radiator, since an old, clogged radiator wouldn’t be up to the task to properly cool the engine. But that wasn’t it.
We also like the “Theory of Last Touched.” In that theory, we say that when something goes wrong, look at what you did last on the car that could have created the new problem. Not that you did anything wrong; just cause-and-effect that led to the new issue.
Here’s an example. I had a 924S that had a bad reference sensor plug – plastic falling apart in your hand. The plastic on the harness was good, so I obtained two new sensors and replaced them. Start, run, drive – all good. A couple of days later I noticed that the car was running a little hotter than before – not much more, but a little. The coolant level was fine, so what could be wrong? I did nothing to the cooling system – the reference sensors have no connection to the cooling system. So the search begins – fans, fan switch, thermostat…what could it be?
If applying the “theory of last touched,” the first place to start is to review whatever I did before – whatever I last touched on the car. In going over the processes that I used and the things that I did, I remembered that when I did the reference sensors, I disconnected the heater hose from the back of the intake to get better access to the reference sensors. The hose did not drip, was off for a grand total of about six minutes and was reinstalled. So I checked the hose clamp, and it was tights.
No drip, huh? So for fun I bled the cooling system to get rid of any air that may have entered the head and got trapped in the back of the head. I did actually get a little air out of it, warmed up the engine and all was fine. A search that could have taken a day or more was fixed in a couple of minutes. Should I have known better? Sure, but the Proper Application of the Theory of Last Touched solved the problem quickly.
In our suggestions, we thought that he should try the following:
- Check grounds, especially behind the dash, especially the one at the top of the dash above and in front of the gauges. (on the driver side in our RHD cars, but unknown in the LHD cars.) Also put a temporary ground between the engine and the negative side of the battery to be sure that the engine is getting adequate ground.
- Check/change the sending unit for the gauge, including the connector. (We would think that corrosion on the sending unit would provide a lower reading, but…)
We also suggested that he get a temp gun to actually check the temperatures at various locations to see if there were any hot spots. Honestly, if there were any restrictions the temp gun would be the right tool to figure it out.
There is also a difference between the 944 lower hose and the 924S lower hose – the 944 hose is a little longer where it attaches to the radiator, and if you use the 944 hose on a 924S, there can be a small kink in the hose, restricting flow from the radiator to the water pump. If we adapt the Theory of Last Touched, that could be the problem if the lower hose was replaced with new as part of the initial belt/water pump service. Note that the part number for the 944 bottom hose is 94410623707, while the part number for the 924S is 94410623706 – different hoses.
Have any ideas? Post them below for Alan (and us) and let’s see if we can solve this problem for our friends across the pond!
If you drive a 924 or 924S, consider joining the Porsche 924 Owners Club. Great group and great resource. Remember though that they refer the Audi-engine Porsche as a 924 2.0 and the 924S as a 924 2.5. As popular as they are there, you will find a variety of used parts sources that will work in out LHD cars here in the colonies!