Overheated!

[forestnut]

Hi, have had a problem with my 1993 520 overheating, have looked through forum and can't find an answer to this one! Car runs fine temperature is at normal, if I do any distance of driving or sit in traffic car overheats. For example, drove 140 miles yesterday, no problem, on the return journey, had to stop at motorway services, got back in the car, couple of miles down the motorway the car had overheated! Has anyone else had a similar problem? And is there a solution, apart from don't stop and have a wee break?!!

Have flushed block and radiator - no obvious debris. Thermostat tested working correctly. Think fan is connected the right way round.

Cheers for any help you can give.

[uscharalph]

Hi, have had a problem with my 1993 520 overheating, have looked through forum and can't find an answer to this one! Car runs fine temperature is at normal, if I do any distance of driving or sit in traffic car overheats. For example, drove 140 miles yesterday, no problem, on the return journey, had to stop at motorway services, got back in the car, couple of miles down the motorway the car had overheated! Has anyone else had a similar problem? And is there a solution, apart from don't stop and have a wee break?!!

Have flushed block and radiator - no obvious debris. Thermostat tested working correctly. Think fan is connected the right way round.

Cheers for any help you can give.

How high did the needle get? Was it high right away when you re-started the car or did it start to overheat a couple of miles down the road?

[forestnut]

How high did the needle get? Was it high right away when you re-started the car or did it start to overheat a couple of miles down the road?

More or less straight away and the needle couldn't get any further over to the right!! It had run out of red! Called the recovery truck and they refilled rad by the roadside and bled it. Ran ok, all the way home (another 100 miles),
but to be honest can't work out why it overheated so badly. Surely you can drive a 5 series, stop for a five minute break at the motorway services and carry on without the car overheating?! Or do you know if this is a known design fault rather than just a problem with my car?

Thanks for your help.

[uscharalph]

I had a similar experience. I first changed out the fan clutch, but this didn't totally solve the problem, but it go somewhat better. I ended up changing out the radiator, which had some return to the overflow blockage issues. I also had some problems with the heater core, which was slowly leaking coolant. I bypassed it.

I know this probably doesn't help you too much.

[tye1138]

Few things to try:

1) Bad thermostat: The car would heat up and not keep cool EVER

2) Bad temp sensor: The car would run fine, not overheat, but the dash would think it was overheating.

3) Air bubble trapped in system: The car would drive fine and then all of a sudden start to overheat uncontrollably till you let it sit and then it would get back to normal again.

4) Bad fan clutch: The car would overheat while sitting around, but the temp would get back to normal after you started going.

5) Bad electric fan or sensor: The car would overheat while using the AC, or when its not being cooled properly by the main fan.

First step is to make sure your fan clutch is working. Drivers side of the car, spin the fan towards you, clock wise. If it spins freely, you have a bad clutch. If it has some resistance, its probably OK.

Second step, see if the electric fan starts spinning when the AC is turned on and the car is hot.

If both things are working try this:

I would make sure your tep sensor is working. If you think its working, I'd move on to emptying out the entire cooling system, checking the hoses on the front of the motor and back of it. Make sure you drain ALL The coolant out from the back block drain plug too!

Put in a new thermostat (its cheap and it fails) and re assemble everything.

Make sure your using BMW or aluminum certified coolant ONLY. Standard 50/50 mix and make sure the heat is on when re-filling and testing. The air bubble issue will be fixed and the thermostat replacement should resolve everything.


If you had a bad water pump or bad radiator, you'd probably know. Dirty water coming out of the system AND OR leaking out of the water pump are two major signs of troubles.

Anyhow, try what I talked about and see what happens!

[forestnut]

Cheers for your advice I'll let you know whats happens
Thanks Dave

[forestnut]

Cheers
I'll let you know what happens

Dave

[califblue]

Either you had air in the system or you fan clutch is going south...it should sound like a helicopter while driving slow.

[forestnut]

Cheers everyone for your advice. New fan clutch helped but still overheated, new themostat now fitted and 50/50 mix of collant seems to of done the trick

Cheers again