What should the transmission temperature be?

jonespm · Post by **jonespm** » Mon Apr 15, 2019 6:09 am

Hi,

I have a 2010 E89 Sdrive35i and a few weeks ago the transmission overheating warning came on and off after about 20 seconds (22 degrees day, driving in traffic). A few days later I checked the transmission and clutch temperatures after town driving for 30 minutes and they where about 83 degress. Two weeks later the warning came on again (23 degrees day, town driving) and again today (26 degrees day, town driving) but this time I had my diagnostic tool with me and when I checked the tempratures and they about 102 degrees. Hotter certainly but I would have thought not hot enough to warrent the warning lights. On all occassion the oil temperature was normal.

Does anyone have any idea what the normal termperature range is for a 35i DCT transmission?

Cheers, Peter

Stuartt · Post by **Stuartt** » Mon Apr 15, 2019 6:55 am

jonespm wrote: ↑Mon Apr 15, 2019 6:09 am Hi,

I have a 2010 E89 Sdrive35i and a few weeks ago the transmission overheating warning came on and off after about 20 seconds (22 degrees day, driving in traffic). A few days later I checked the transmission and clutch temperatures after town driving for 30 minutes and they where about 83 degress. Two weeks later the warning came on again (23 degrees day, town driving) and again today (26 degrees day, town driving) but this time I had my diagnostic tool with me and when I checked the tempratures and they about 102 degrees. Hotter certainly but I would have thought not hot enough to warrent the warning lights. On all occassion the oil temperature was normal.

Does anyone have any idea what the normal termperature range is for a 35i DCT transmission?

Cheers, Peter

Hi Peter, sorry I can’t help you with your answer but there is a dedicated DCT Facebook group that may well be able too.

https://www.facebook.com/groups/2011679 ... ?ref=share

There seems to be some very knowledgeable people on there.

Stuart

jonespm · Post by **jonespm** » Mon Apr 15, 2019 7:21 am

Thanks Stuart, have also posted to the FB page..

Cheers, Peter

R.E92 · Post by **R.E92** » Mon Apr 15, 2019 3:41 pm

Fully warmed up the DCT should be around 82C and I wouldn't expect it to get any higher. There's 7L of fluid for it to heat up so it takes around an hour of cruising on a motorway to reach that but I imagine start stop traffic should heat it up quicker.
I've only ever timed the transmission warmup once and that was on a long motorway journey at 9C ambient temperature.

Something sounds wrong with the transmission, overheating is quite often caused by clutch slip. Has the car been modified at all?

A leaking sump on the DCT is quite common, I would check that out as a priority. I'm not sure if the transmission has a fluid level monitoring but a low fluid level would cause overheating.

A new sump and fluid at BMW is circa £1500. At a skilled independent I would expect £800-900.

jonespm · Post by **jonespm** » Tue Apr 16, 2019 12:23 am

Thanks a lot for that - now I know that 100 degrees is too hot then into the shop it goes!!

Just a quick follow up if I may. I bought the car at 30k and its now done 120k and I just use it as a normal daily driver and I'm pretty sure the previous owner did, i.e. no track days or pressing hard. In this case is 120k a bit early for problems or is this reasonably common with a DCT?

Cheers, Peter

R.E92 · Post by **R.E92** » Tue Apr 16, 2019 8:56 am

jonespm wrote: ↑Tue Apr 16, 2019 12:23 am Thanks a lot for that - now I know that 100 degrees is too hot then into the shop it goes!!

Just a quick follow up if I may. I bought the car at 30k and its now done 120k and I just use it as a normal daily driver and I'm pretty sure the previous owner did, i.e. no track days or pressing hard. In this case is 120k a bit early for problems or is this reasonably common with a DCT?

Cheers, Peter

Aside from the leaking sump, the DCT is a very reliable and "over engineered" gearbox.
The sump is something that needs replacing on most cars above the 50k mark, so you are well beyond that.

jonespm · Post by **jonespm** » Thu Apr 18, 2019 12:38 am

FYI - sump leak it is. Goes in next week.

For completeness I will report the actual problem and cost to fix when I have it..

Cheers, Peter

jonespm · Post by **jonespm** » Tue May 07, 2019 6:29 am

Hi,

Finally have the Z4 back and the problem was interesting.

There's an inspection plate on the side of the gearbox which looked to be leaking. Fortunately my guy really inspected the issue and found the leak was actually at a seal around the wiring harness entering a housing on the top of the gearbox. The oil was leaking out from the seal and making its way into some kind of 'webbing' then leaving there via a hole and dripping down the side of the gearbox onto the top of the inspection plate.

Total cost (Aussie Dollars): $2450

$ 770 - seals, garkets and new trans filters.
$ 440 - oil
$1240 - labour - don't know how many hours but the gearbox had to be removed of course.

I don't know but I think the seal in question may be part: 28607849555

This was the first time my shop has seen this problem but they suspect it may be a generalised DCT issue as the milage build up - my car has 125,000 kilometers on the clock.

Again, thanks for the help in sorting out this problem quickly.

Cheers, Peter

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