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T-Cut · 27th April 2015, 23:16

When an engine works hard it will get hotter than usual, including the diesel. How hot will depend to a large extent on the integrity of the cooling system. The radiator fan must work as designed to keep the engine within normal temperature limits. On the diesel, the low speed should trip on at 105C or so. Since you have the later 2-speed fan, the slow speed resistor should be checked because they're prone to failure. This causes loss of fan cooling until the engine's much hotter. The resistor/low speed can be checked by running the so-called Demist test.

With a cool engine, turn the ignition on and press the Demist button. This effectively invokes the aircon system which requires the slow speed fan. It should start immediately and run continuously until Demist is pressed again (off). If the fan doesn't start immediately, then the resistor has failed. If you repeat the test with the engine on tick-over, the high speed fan will eventually start up and pulse on and off every 10-30 seconds. This is the emergency cooling which will also be tripped on if/when the engine approaches 120C. This also assumes an operational aircon system.

A replacement resistor should be fitted asap, though I realise that's easier said than done in the circumstances. As an emergency measure the failed resistor could be cut out and replaced using heavy gauge wire and good cable connectors. This will give high speed cooling instead of low speed, but is better than nothing. I'd also suggest knowing how to run the trip screen diagnostic mode so you can display the actual running temperature. The standard gauge is of little use to you.

The fan system is permanently live, so any such work must be done with the 80amp fuse removed in the engine bay fuse box or with the battery disconnected.

TC

27th April 2015, 23:16	#2
T-Cut This is my second home Rover75 and Mreg Corsa. Join Date: Nov 2006 Location: Sumweer onat mote o'dust (Sagin) Posts: 21,754 Thanks: 341 Thanked 3,660 Times in 2,924 Posts	When an engine works hard it will get hotter than usual, including the diesel. How hot will depend to a large extent on the integrity of the cooling system. The radiator fan must work as designed to keep the engine within normal temperature limits. On the diesel, the low speed should trip on at 105C or so. Since you have the later 2-speed fan, the slow speed resistor should be checked because they're prone to failure. This causes loss of fan cooling until the engine's much hotter. The resistor/low speed can be checked by running the so-called Demist test. With a cool engine, turn the ignition on and press the Demist button. This effectively invokes the aircon system which requires the slow speed fan. It should start immediately and run continuously until Demist is pressed again (off). If the fan doesn't start immediately, then the resistor has failed. If you repeat the test with the engine on tick-over, the high speed fan will eventually start up and pulse on and off every 10-30 seconds. This is the emergency cooling which will also be tripped on if/when the engine approaches 120C. This also assumes an operational aircon system. A replacement resistor should be fitted asap, though I realise that's easier said than done in the circumstances. As an emergency measure the failed resistor could be cut out and replaced using heavy gauge wire and good cable connectors. This will give high speed cooling instead of low speed, but is better than nothing. I'd also suggest knowing how to run the trip screen diagnostic mode so you can display the actual running temperature. The standard gauge is of little use to you. The fan system is permanently live, so any such work must be done with the 80amp fuse removed in the engine bay fuse box or with the battery disconnected. TC Last edited by T-Cut; 27th April 2015 at 23:31..