{mosgoogle} A common 928 problem is running hot - particularly with the 32V engined cars (S4 onwards). Lots of parts of the 928 system can affect the temperature.

The radiator of the 928 was not increased in capacity as the engine increased from 4.5 to 5.4 litres. With the move to the 32V engine the mechanically driven cooling fan was replaced with 2 electrically driven fans and the nose of the car was also equipped with automatic electrically driven cooling flaps that controlled the amount of air entering the engine bay. Sounds somewhat 'heath robinson' but it works well if its looked after and there are a number of failure points so nothing is likely to be catastrophic. You will notice increased temperatures because of one failed fan but can still get home for example...

Correct Temperature

A 928 should run at approx 85 degrees - ie approximately half way between 80 and 90 on the temperature gauge. This is in all driving conditions - this temperature should even be maintained in heavy traffic with the air conditioning on when the weather is hot. Many mechanics (including Official Porsche Dealers) will try and tell you that "all 928s run hot". This is not true - its just that a lot of 928s have cooling problems!

Water Pump

If your temperature suddenly just rises into the red line the obvious problem is a failed water pump. These are expensive to replace as they involve the refitting of the cam belt and 928UK recommends that a new water pump is fitted whenever the cam belt is changed because a new belt strains an old water pump and failure often follows. Trust us this is a proven recommendation not an old wives tale.

Radiator

The radiator is an obvious source of a hot engine. Although your radiator may be fine in itself check that its not clogged up with leaves and stray matter. A particular problem area is between the air conditioning radiator and the main radiator. This area is hard to access without removing at least one radiator but may be the root cause of a hot engine.

Of course the radiator itself may be damaged - if so then a replacement unit is the only expensive solution. In a very hot climate - or if an engine is modified for more power - a bigger radiator may be required. American tuners like Devek have developed bigger capacity radiator kits.

Cooling Fans

On 32V engines the fans are electrically operated. You must check that both come into operation with full force when the engine is hot. Sometimes a fan will appear to work but isn't performing as strongly as it should and will lead to a hotter engine.

Front Nose Flaps

The nose flaps on the S4 and GT were electrically operated. The idea was to close them off when the engine was cold so that it would warm up faster and then open up when the engine was warm to allow air in to cool the radiators. It is telling that even Porsche thought this an over complication when the idea was dropped with the introduction of the GTS - the flaps were mounted permanently open. In fact many S4 / GT owners remove the fuse on the flap in the open position thus removing it as a source of an overheating problem.

Thermostat

Like any component the thermostat in the radiator can fail. A new thermostat is relatively cheap - in fact many owners opt for a lower temperature thermostat (75 degrees, down from 83 degrees) to help their engines run cooler.

Water Wetter

Another option worth considering is adding water wetter to the coolant mixture. Water wetter increases the heat transfer capabilities of the coolant mixture and will thus increase the cooling capacity of the entire water cooling system. A popular brand is Redline Water Wetter which is suitable for a 928 engine.