XSeries-forum

Afternoon chaps, it's been a while since I had any problems but a new bunch have occurred, while I must add the car runs great still but!
Whilst cleaning my engine bay one day I noticed (because if it's nice bright pink colour) my water resivoiur seems to overflow a little? I don't seem to be losing too much water but it's hard to tell really, I just noticed staining round the cap, it's never happened before but I need to get to the bottom of it!

Several possible reasons for this....

Nicest first...

1.Contamination on mating surfaces of cap seal ring to sealing surface face of expansion bottle. Sometimes a precipitate chalky appearance on the parts - which is porus.  Clean parts...possibly  replace rad cap.

2.Cap sealing rubber perished...    replace rad cap.

3.Thermostat jammed closed/partially closed and engine too hot causing pressure venting from cap. Replace Thermostat.

4.Head gasket failure causing coolant to be pressurised from compression gasses.
There may be tell-tale signs of oil film on coolant surface.
The head gasket failure can be easily remedied by a bottle of "Real-Steel" which will permanently fix the gasket (if the gas leak is minor), or strip engine & change head gasket.

How much coolant is leaking ?
Does the temp remain stable at instrument gauge ?
Is coolant level still good... hinting at a very minor leak ?

1st task is too change the Rad Cap, clean any debris from expansion bottle sealing surface...and see what happens...

Regards
Grant B

Thanks for the reply, I have checked oil and water as I thought it could be the head! But water is 100% free of oil and oil is pure oil, the cap rubber seal looks ok, the car temp gauge never goes higher than half gauge, I have a minor oil leak somewhere and I did over fill with oil once and I had a "oil pressure fault" warning on the bc for a few minutes one day. The over flow water problem seem to stem on the same trip I did that, but that was a 1000 miles ago and oil levels are perfect now and have been for ages????? 

Well... a radiator cap generally only ever gets changed when it leaks...
Maybe its leaking....

Its the cheapest fix and the 1st thing Id change if I were you...

Change it and see what happens.

The temperature gauge should be in the middle for a certain temperature range, if you want to see exactly what the temperature is, you should be able to unlock the OBC. This link worked for my 02 http://www.bimmerforums.com/forum/showt ... uter-(OBC)