BMW 325 ci (2002) - overheating woes

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Tue 23 Mar 2010 21:48
BMW 325 ci (2002) - overheating woes - Gregory II

a friend of mine has a bMw 3-series (2.5 ci). the car initially had a faulty fan; this meant that it did not actuate when the engine was becoming very warm. the engine therefore overheated.

Upon replacing the fan (an aftermarket replacement was used), the fan worked for a around 1 week when it then failed again.

is this a known problem on this car, and is there a known cause for this problem.

i am thinking along the lines of relay, wiring or thermoswitch causing this fault. what would be the most likely reason why the fan keeps failing and how can it be tested?

it should be noted that the expansion tank has split letting the coolant out. i am not sure if this related, but the overheating probably caused the expansion tank to split with the over-hot coolant.

thanks for any thoughts

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Tue 23 Mar 2010 22:03
bMw 325 ci (2002) - overheating woes - Peter.N.

if the fan has been changed the next thing to check is the sensor, if you short the contacts together it should make the fan run if its faulty.

Under what circumstances does it overheat? if its doing it in normal driving something other than the fan may be causing it, when the car is moving there should be sufficient air through the radiator due to the ram effect to cool it without the fan running, if it overheats under these conditions i would suspect a faulty thermostat.

i doubt that the excessive temperature would be the cause of the header tank failure, probably just that the plastic has hardened.

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Tue 23 Mar 2010 22:19
bMw 325 ci (2002) - overheating woes - elekie&a/c doctor

the cooling fan circuit is electronically controlled from the engine management control ecu(dme unit).attached to the fan motor housing is an electronic speed regulator .this receives a signal from the ecu and requests the fan speed dependant on cooling demand.You need to have the system tested with diagnostic equipment.Don't be tempted to short or bridge any wiring otherwise serious damage may be inflicted.hth

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Tue 23 Mar 2010 22:49
bMw 325 ci (2002) - overheating woes - Gregory II

the vehicle was tested for codes and no problem codes appear. My friend knew by bridging the wires it could inflict damage; for the price of a workshop manual (haynes - service manual preferred), the correct procedures can be carried out to test items.

what should the next step be?

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Tue 23 Mar 2010 23:01
bMw 325 ci (2002) - overheating woes - Peter.N.

Sorry - i'm out of my depth then, i don't run anything made after the mid '90s

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Tue 23 Mar 2010 23:05
bMw 325 ci (2002) - overheating woes - Gregory II

i don't really think cars have changed that drastically over the years from a mechanical point of view. there are obviously changes, but the fundamentals still apply!

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