2007 3.0 Si - 85k

W

Weelawser

Member
 Aberdeenshire
Folks,
Car has been off the road since last year, went to start her up the other day to check things over and once warmed up the temp gauge would rise then fall when the fan kicked in but not in the normal way, switched the engine off to investigate further.
Prior to taking her off the road the coolant expansion tank had been losing water but only when the engine was hot and not all the time.
First thoughts were the dreaded FCHG, second were thermostat / water pump, took off the expansion tank, can't see any cracks, no scummy residue in the oil filler cap, all hoses seem ok, would I be best getting a compression test and coolant check ?
I was thinking of just replacing the expansion tank as it seems to be a common problem and it is the original tank.
Thoughts ?

Cheers,
Paul
 
So was the expansion tank full?

Shortly after we got wifey's E85 I noticed water on the engine undertray.
The expansion tank level was low.
No signs anywhere of a leak. I changed it anyway, and once I started taking it all apart I found it was leaking from the O-ring seal at the bottom, where it pushes down into the housing.
 
That's one of the areas i am suspecting, always topped up with water when required....Any idea where to get the o rings from or did you replace the tank ?
 
Weelawser said:
That's one of the areas i am suspecting, always topped up with water when required....Any idea where to get the o rings from or did you replace the tank ?
Click to expand...

I replaced the tank because at that point I suspected it had a hairline crack. Yours may have, it's hard to tell as they tend to open up when hot.
It is a bit of a fiddle to get out so I think my advice may be to change the tank anyway, or you could end up going back in again.
Mind you, I also had one of those big boxes full of various sized O-rings so I was able to replace the hose ones etc while I was at it.

By the way, mine is an earlier M54 car, but I think I'm right in saying they are very similar.

You could start by running it until hot then popping the bonnet and looking to see if there's any drips below the tank?
 
Thanks, yes I already have the tank off, think i will just replace anyway. Did you go for BMW part or OEM ?
 
Very common - the expansion tank only leaks under pressure, usually in the form of a hairline crack so hard to spot when engine is cold. BUT, if the level in the expansion tank is normal and you are getting strange temperature swings it will be the water pump for sure. Head gasket failure is pretty rare on the N52 and virtually unheard of on the N52K (not sure which you have).
 
Thanks for the advice, possibly with her lying for the best part of 8 months unused apart from the occasional start up gunk has built up in the pump I guess. Perhaps a new pump may be on the cards also, best place for parts ?
 
Weelawser said:
Thanks, yes I already have the tank off, think i will just replace anyway. Did you go for BMW part or OEM ?
Click to expand...

I got a Hella one from Autodoc. Arrived in about a week. I got that one as it included the level sensor, but not all of them do.

As it is a generic one for various other models too, it comes with a plastic tab on the top that has to be removed, simply clips off.
 
Weelawser said:
Thanks for the advice, possibly with her lying for the best part of 8 months unused apart from the occasional start up gunk has built up in the pump I guess. Perhaps a new pump may be on the cards also, best place for parts ?
Click to expand...

Pierburg make the oem one. Plenty available around the £200 mark on Ebay. Might want to change stat while you are in there.
 
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