Engine Cooling

Overheating Problem - Major

Overheating Problem - Major

My 928 and I have just had the dubious pleasure of a 140 mile flat-bed trip from Newark to London after a seemingly serious overheating. I'm hoping someone may throw some light on what the cause might be.

The first I knew was when the red message 'Engine overheating!' came on and the temperature gauge was in the red portion. I immediately turned right off the road and stopped the engine. Fans were not running with ignition off, but ran as soon as ignition was switched on to position 1. Coolant level was normal. No sign of steam or leaks. I could hear a slight bubbling sound when sat in the car (maybe from heater matrix, maybe from engine block or hoses).

I left the fans running a while, and temp gauge eventually dropped backto 100. Cautiously restarting the engine, I could see the needle creep back up into the red again, so I switched off and gave up.

My suspicion is no coolant circulation, so water pump failure (or closed thermostat?). But could it just be a sensor problem? If so, how to check? Anybody got any other ideas please.

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Jonathan M Rackowe
JMR Technical Services, London, UK

1991 928GT, Manual, Baltic Blue/Linen

This recently happened to an 87 S4 Auto that I know and it was the thermostat. Inspection showed it was sticking, there was a shiny spot showing the drag/stick point. Number one is to change the thermostat and o-ring gasket. It's in the lower radiator line where it connects to the engine.

Good luck,

Marc White

I have just had the water pump in my 86.5 replaced, mine was also overheating. The problem was caused by the plastic impeller on the water pump spinning on the shaft (lousy design). You can't tell that this is the problem without removing the water pump - costly unfortunately.

Mine seemed as if it was circulating the coolant, but in fact it was failing under load.

good luck.

Brett Read
928S 86.5 Auto

Just back from the shop: Yes, my problem turned out to be exactly that - detached impeller. Previous owner had t-belt changed in 1995, but not the water pump.
Jonathan M Rackowe

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