Radiator fan running constantly

[hod05]

Hi guys

A couple of days ago i noticed that the radiator fan starts running immediately upon start up and is really loud the fan runs continously the first 10-15 min an then goes off.

Its as if the fan is running full blast like the car thinks its overheating however the engine cannot be overheating as it happens immediately upon startup. I've checked the water level and it's fine no other problems an engine runs fine. The temperature slowly climbs to the normal level (about 80) and stays there

Im concerned that the fan will delay the engine warming up and is causing over cooling

Any ideas?

 

[Rappey69]

Air con is on maybe ? (total guess)

 

[LostKiwi]

The fan runs if it doesn't receive a signal from the ECU.
It can therefore be SAM, ECU or Fan controller.

It won't over cool as the thermostat will control the engine temperature.

 

[hod05]

Thanks for your reply there's no ce light or any warning light on bit worried if it could be ECU that won't be cheap surly a ECU fault would cause other issues? What is the SAM?

 

[alexanderfoti]

It will also run if there is a communication issue with another ECU. EG gearbox ECU disconnected will cause fan to run on full blast. I would assume that there is an intermittent communication issue with something not critical to driving.

 

[hod05]

It will also run if there is a communication issue with another ECU. EG gearbox ECU disconnected will cause fan to run on full blast. I would assume that there is an intermittent communication issue with something not critical to driving.

thanks for the responses.

having looked again the fan does not start up right away but starts about 30 sec to a min after the engine starts fan runs but seems to stop after a while. I drove the car home (5 miles) then switched off let sit a min and restarted the engine and the fan did not come on however tomorrow it will probably do it again.

another guy on this forum seems to have had a similar issue with a c250 and it was the air con sensor.
The advice given to him is that if fan comes on immediately with ignition then its ECU but if it takes a min or so its some other sensor/module

I really hope its not the ECU 900+ VAT

 

[LostKiwi]

Get it on STAR and have the sensors checked out.

 

[hod05]

Il get it looked into although it didn't do it at all this morning

 

[davemercedes]

I didn't know the tecchy bits posted above - thanks, chaps.

Il get it looked into although it didn't do it at all this morning

Fingers X'd it's nothing more than a sensor...

 

[hod05]

Started doing it again so booked in for checking still no CEL and no messages on service assist the fan goes off when engine up to temp so it's as if it's coming in when cold and off when warm does not run constantly as previously thought.