Cooling fan on from start - L series FL1

Posted on behalf of a colleague - I don't know much about Doozels......

Engine has started to hunt a little - warm or cold revs fluctuate on idle.

Cooling fan comes on as soon as the ignition switch is turned to position II.

Does not happen all the time - often nothing then after 30 seconds fan comes on and then goes off after a minute.

No signs of overheating - plenty of coolant.

Any ideas?? I'm thinking a sensor causing ECU to failsafe and apply fan power...

Thanks in advance - can't seem to find anything like this in search.

Steve.

I remember last time while bleeding my cooling system...

I'd started the engine up and drove around the garage but the cooling fans came on straight away, went off and would come on again. Also my revs were fluctuating.

I parked back up, bled the system some more and all was fine.

That's on my K series though so not sure if the same would happen on a diesel.