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Discussion Starter · #1 ·
Hi all,

My father-in-law has just asked me to look at his E39 535i auto as he's found oil in the coolant expansion tank whilst checking the fluid levels. He was (understandably!) worried about head gasket failure - which could write the car off.

I've had a good trawl of this site and the other BMW forums out there, as well as Google, and haven't turned up anything

There was definitely oil in the expansion tank, but only a tiny amount of "mayonnaise" - there was no white mayo under the oil filler cap or any evidence of water in the engine oil on the dipstick.

I did some level checks, and took samples on a white towel of the oil in the expansion tank as well as the engine oil and PAS fluid from the reservoir on the right of the engine bay.

What it shows is that the oil in the cooling system matches the colour and shade of the PAS fluid (which I believe is ATF), and is too "orange" and light in colour to match the engine oil.

So I'm fairly confident that the "oil" in the coolant is infact ATF - however I now need to find out where it has come from.

As far as I can work out the power steering and autobox both use ATF and have coolers. I've had a look on thge BMWFans ETK and neither of these seem to be coolant-to-fluid, they both seem to have separate air-to-fluid heat exchangers:

ETK Transmission cooler
PAS fluid cooler

So, my question is - how can the ATF/PAS fluid have got into the cooling system?

I have found the following diagram on the ETK which appears to show a water-to-oil cooler (part ID 1, bottom middle), with a gearbox at the top, and the cooler is listed as "automatic only". Due to poor visibility in the engine bay (big lump of a V8!) I've not been able to determine exactly where on the car the pipes connected to this cooler go.

Mystery oil cooler

All and any advice welcomed :thumbsup

Thanks very much,

Martin
 

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IIRC the auto gearbox fluid cooler is built into the radiator, so the coolant rad and A/T cooler are 1 unit.
Ive seen this before on another vehicle where the rad has fractured internally causing the 2 to mix. I sent the rad away to a specialist, and they tested it and confirmed..:thumbsup
Let me know how it goes..:cool
 

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Discussion Starter · #3 ·
Hi Steve, thanks for your reply.

The E34 definitely had the oil cooler built into the rad - a fractured rad was my first thought when I found out it was ATF not engine oil.

However the E39's air-to-ATF cooler is a separate rad (see my 1st link above) :(

I've done some further Googling and the item in my 3rd link does appear to be a water-to-ATF heat exchanger - so I suppose the question now is: are these known to fail?

I know a pressure test would be the only way to be certain, but I'm trying to gather some information before the car is pulled apart :)
 

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It could well be the water to ATF heat exchanger, I've seen one fail on a Renault before, and I have a distant memory of one getting replaced on a BMW at my old work due to this. :)
 
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