Fans on radiator - what are they both for?

[northnoble]

Apologies, but another daft question. The two fans on the front radiator of a 2002 M12 (2.5) are they both linked to the cooling system, or is one part of the air conditioning system???....why the question, occasionally my car runs a bit hot, when I stop and look only one fans is running (but if I put the air con on, the other one kicks in)

Most of the time the temp guage sits bang on 90, but occasionally it goes up to 110 for about five minutes before suddenly jumping back to 90...any ideas???

Thanks.

[mr-manners]

mine did the same thing when i bought it,it turned out to be loose connections,just played with the fan wires while one was working and the other kicked in, works fine now

[AMG Merc]

Both fans are for engine cooling and both should go on and off together as the engine heats and cools. IMHO, your range of temp movement is abnormal so you should check for leaks, thermostat, etc.

AFAIR, normal for me is around 90deg deviating ony 1-2 points upwards in heavy traffic.

PS - also, 1) spin the fan that isn't working up by hand to see if its seized.
2) when the good fan is running put a meter on the other (bad) fan power feed to see if you have 12v there present.

Edited by AMG Merc on Saturday 7th March 13:30

[northnoble]

Checked it again today - no loss of coolant but only one fan coming on...until I switch the air con on??????

Going to book it in to get checked out as it ran at 110 degrees for about 10 mins before returning to 90 !!!!

[paulcundy]

Only on efan is actually needed for engine cooling. The OEM Noble water gauge is very inaccurate and sits on 90 most of the time no matter what the actual temperature is. One cars like Richard and mine where we have alternative sensors inputs my car will blat about the circuit with teh temp at a fixed 90 but when you come in the pits unless the fan is turned on it can quickly get to 110-120 with the engine just idling but stattionary. With one fan on its enough to keep it at 90.
Regards
Paul C

[ThatPhilBrettGuy]

paulcundy said:

Only on efan is actually needed for engine cooling. The OEM Noble water gauge is very inaccurate and sits on 90 most of the time no matter what the actual temperature is. One cars like Richard and mine where we have alternative sensors inputs my car will blat about the circuit with teh temp at a fixed 90 but when you come in the pits unless the fan is turned on it can quickly get to 110-120 with the engine just idling but stattionary. With one fan on its enough to keep it at 90.
Regards
Paul C

Ah but remember 90 is fake. It really just means 'normal' and has no relation to that actually temperature. The gauge connects to the ECU and in simplified form when it's running 90 = normal, 110 = too hot. That's why you don't see much in between

[mgbond]

The mbe on the 3ltr cars controls the gauge, on the 2.5 it does not so it will sit at 90 and rise to 100 ish before the fans kick in. Both fans come on at a slower speed when the air con is on. Both fans should come on when temp hits 100 ish. When I had my new rad fitted and system flushed the car runs at about 85 gauge now and takes a good while to get to 100. So get the fan sorted and might be worth flushing the system

Bondy

[YellowShed]

ThatPhilBrettGuy said:

Ah but remember 90 is fake. It really just means 'normal' and has no relation to that actually temperature. The gauge connects to the ECU and in simplified form when it's running 90 = normal, 110 = too hot. That's why you don't see much in between

Only on later 3s, 3Rs and M400s. The early cars had a direct feed from the temperature sensor to the gauge.

YellowShed

[ThatPhilBrettGuy]

Ah right. Does that get changed if the 2.5 has had the spaghetti ECU swapped out for the MBE one?

[paulcundy]

ThatPhilBrettGuy said:

paulcundy said:

Only on efan is actually needed for engine cooling. The OEM Noble water gauge is very inaccurate and sits on 90 most of the time no matter what the actual temperature is. One cars like Richard and mine where we have alternative sensors inputs my car will blat about the circuit with teh temp at a fixed 90 but when you come in the pits unless the fan is turned on it can quickly get to 110-120 with the engine just idling but stattionary. With one fan on its enough to keep it at 90.
Regards
Paul C

Ah but remember 90 is fake. It really just means 'normal' and has no relation to that actually temperature. The gauge connects to the ECU and in simplified form when it's running 90 = normal, 110 = too hot. That's why you don't see much in between

Sorry, not clear in my posting that the figures I quoted, 90, 110-120 are actual real temperatuse from real sensors not what the OEM Noble gauge would indicate. That indicates 90 just about all the time for the reasons stated!
Paul C

[northnoble]

Problem sorted - sticking thermostat !!!!