E92 m3 - Milky oil in DCT gearbox (coolant in DCT oil?)

[gordon513]

Hi all,

I am a slight loss here.

For context, my car is a 2010 E92 M3 DCT non-comp.

I started to get a judder / hesitation when cruising and the car was under load (e.g. going up a hill on cruise control - c. 3k RPM).

It initially felt like a misfire so I have been going through the motions with that - running the misfire test with ISTA, replacing coils etc.

It then occurred to me that it might be clutch slip. I took the car out for a test drive to try and replicate and finally got 2 codes -

5A54: Transmission overheating: Phase Black
5A58: Spray-off sensor: electrical defect


The gearbox was serviced about 8k miles ago. I thought maybe the oil was low so went to have a look today, and I was shocked that a load of milky oil came out the the fill plug (pics below).

Could anyone help me with how this might have occurred? And what next steps I should take (apart from obviously not driving the car)?


I have a small coolant leak from one of the o-rings on the engine thermostat housing which must have perished over time, and does drip a bit - you can see some dried coolant on the DCT pan. It was next on my 'to-do' list. But I can't imagine that this could have got into the gearbox?


I have made a similar thread on a different forum too, wanting to maximise chances of someone having also experienced this!


Cheers all.

[spammysammich]

There is a heat exchanger on top of your transmission that could have sprung an internal leak allowing coolant and transmission oil to mix. Sounds expensive.

[gordon513]

Originally Posted by spammysammich

There is a heat exchanger on top of your transmission that could have sprung an internal leak allowing coolant and transmission oil to mix. Sounds expensive.

Yup - was looking on realOEM and saw that. Would the oil not be under much greater pressure than the coolant though? i.e. you'd expect the oil to flow into the coolant?

I have no idea how I flush the milky coolant out of the box, plus I assume the clutches are probably cooked at this point.

[Helmsman]

The coolant does share heat exchanger with the DCT fluid and while I've seen other cars having issues with this (Merc) I have yet to read about an M3 with the issue. And agree, one would expect oil in the coolant as well.

Are you absolutely sure that the shop used the correct fluid? Even a BMW dealership poured wrong fluid into my DCT once, which ended up with a new box/cooler/hoses. Fortunately paid by the dealer.

I'd check into that. The fluid have changed part number over the last years but should still be DCTF-1, and nothing else (part no in Europe: 83222446673).

Good luck!

[gordon513]

Originally Posted by Helmsman

The coolant does share heat exchanger with the DCT fluid and while I've seen other cars having issues with this (Merc) I have yet to read about an M3 with the issue. And agree, one would expect oil in the coolant as well.

Are you absolutely sure that the shop used the correct fluid? Even a BMW dealership poured wrong fluid into my DCT once, which ended up with a new box/cooler/hoses. Fortunately paid by the dealer.

I'd check into that. The fluid have changed part number over the last years but should still be DCTF-1, and nothing else (part no in Europe: 83222446673).

Good luck!

Cheers Helmsman.

In the interest of keeping both threads alive.


Coolant dripping from one of the o-rings that comes out of the TSTAT housing and it does loose a fair bit of coolant when driving but I can clearly see it coming from here. Even if there was a way for it to get in to the top of the gearbox (I don't know if there are any open holes on the top of the gearbox - wiring harness?), I struggle to see how it would get in in such a quantity.

Which brings us back to either a) the heat exchanger, or b) incorrect fluid.

To address b) - here is the invoice from the garage that did the DCT service. It was a BMW specialist so I would hope they would use the correct fluid but as you say, stranger things have happened at sea. I do think it is correct though but welcome thoughts?

Also the gearbox is way overfilled - which makes me think somehow coolant is getting in. It came out at pace when I opened up the fill plug and I think if it was at the correct level, it should only dribble out.

Now if it is a) I could either accept fate and pull the gearbox and replace the heat exchanger, lines, filters etc etc and hope that fixes it. Still a question mark on if the gearbox / clutches are already ruined, and how to get all of the sludge out. It would probably be better to source a low millage box although I have no idea how the coding works with the mechatronic unit...

Or I guess I could sort out the leaking Thermostat, replace the oil in the DCT box and drive it around and monitor coolant levels to see of they go down? Shame the oil is so expensive!

[Helmsman]

Originally Posted by gordon513

Cheers Helmsman.

In the interest of keeping both threads alive.


Coolant dripping from one of the o-rings that comes out of the TSTAT housing and it does loose a fair bit of coolant when driving but I can clearly see it coming from here. Even if there was a way for it to get in to the top of the gearbox (I don't know if there are any open holes on the top of the gearbox - wiring harness?), I struggle to see how it would get in in such a quantity.

Which brings us back to either a) the heat exchanger, or b) incorrect fluid.

To address b) - here is the invoice from the garage that did the DCT service. It was a BMW specialist so I would hope they would use the correct fluid but as you say, stranger things have happened at sea. I do think it is correct though but welcome thoughts?

Also the gearbox is way overfilled - which makes me think somehow coolant is getting in. It came out at pace when I opened up the fill plug and I think if it was at the correct level, it should only dribble out.

Now if it is a) I could either accept fate and pull the gearbox and replace the heat exchanger, lines, filters etc etc and hope that fixes it. Still a question mark on if the gearbox / clutches are already ruined, and how to get all of the sludge out. It would probably be better to source a low millage box although I have no idea how the coding works with the mechatronic unit...

Or I guess I could sort out the leaking Thermostat, replace the oil in the DCT box and drive it around and monitor coolant levels to see of they go down? Shame the oil is so expensive!

Googling the Feb39070, ATF (auto transmissions fluid) comes up, which it not what is supposed to be used.
When the (main in Sweden) BMW dealership poured (MT) fluid in my car they argued strongly that it was okay as the DCT is "the same as manual", and only gave in once I pulled in BMW Sweden. So doesn't mean your guys have fuuked up intentionally but sh@t happens.
I'd definitely investigate the fluid used in more detail, if fact regardless of is you have a leak in the cooland/fluid exchanger.

You recon you lose more coolant than you see ending up in the V? I would address that o-ring right away anyhow. Rings are cheap (even from the dealer), grab a couple of extra and get the Tstat off, so with certanty close that possible source.

[gordon513]

All – apologies for the delay in providing an update.

I changed the DCT fluid and drove the car for 50 miles-ish - and it drove fine. However, after draining it again, the fluid appeared milky.

At that point, I decided to stop further diagnosis and instead replaced the gearbox with a low-mileage unit, along with fitting a brand new heat exchanger.

I still have the original heat exchanger and plan to have it pressure tested out of curiosity, but it seems the most likely cause of the issue.