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OK to use synthetic oil in trans and diff?
Posted: Tue Jan 16, 2024 3:40 pm
by cory58
I want to replace the trans and diff oils in my E12 for the first time during my ownership. It's older than any other BMW I've owned by 10+ years. Is it ok to use synthetic oil or should I stick with conventional for the trans and diff? It's the only BMW I've owned that leaks zero fluids!
Thanks, Cory
Re: OK to use synthetic oil in trans and diff?
Posted: Wed Jan 17, 2024 6:18 am
by PatinaBeforePolish
I’ve been using Redline MTL in the transmission and Redline 75/90 in the differential with no problems. Trans actually shifted more smoothly when I switched to Redline which was around 8 years ago.
Re: OK to use synthetic oil in trans and diff?
Posted: Thu Jan 18, 2024 9:15 am
by cory58
PatinaBeforePolish wrote: Wed Jan 17, 2024 6:18 am
I’ve been using Redline MTL in the transmission and Redline 75/90 in the differential with no problems. Trans actually shifted more smoothly when I switched to Redline which was around 8 years ago.
Thank you!
Re: OK to use synthetic oil in trans and diff?
Posted: Thu Jan 25, 2024 9:06 am
by 528i-1981
https://www.firstfives.org/phpBB-3.2.1/ ... hp?p=31333
I recall this being discussed here when I changed mine. LOL Cory, you initiated that thread four years ago. I think we all have E12 items that have been pending for that long or longer. Anyway there's good info in that thread. I've had no issues since making the switch. Cheers!
Re: OK to use synthetic oil in trans and diff?
Posted: Thu Jan 23, 2025 11:31 am
by John in the Glade
Regarding DIFFERENTIAL fluid.
I know this reply is LATE, but worth mentioning. Previous owner had a shop change his differential fluid with generic 75w90. That was a mistake, because the diff would then GROWL after 15-30 minutes of driving.
The remedy is to use HYPOID gear oil. I used Liqui Moly synthetic hypoid gear oil which solved the noise issue.
Perhaps Redline or other similar have hypoid qualities, but I suggest looking for hypoid in the gear oil product description.
Re: OK to use synthetic oil in trans and diff?
Posted: Thu Jan 23, 2025 1:31 pm
by Mike W.
John in the Glade wrote: Thu Jan 23, 2025 11:31 am
Regarding DIFFERENTIAL fluid.
I know this reply is LATE, but worth mentioning. Previous owner had a shop change his differential fluid with generic 75w90. That was a mistake, because the diff would then GROWL after 15-30 minutes of driving.
The remedy is to use HYPOID gear oil. I used Liqui Moly synthetic hypoid gear oil which solved the noise issue.
Perhaps Redline or other similar have hypoid qualities, but I suggest looking for hypoid in the gear oil product description.
The number matters, but it's got to be hypoid for the diff, correct, which is referred to as a GL5 oil. At the same time, trannys should not use hypoid oil, supposedly the sulfur in it will attack the brass synchros, but even if it doesn't it's both too thick and too "sticky" to shift well, especially cold. Trannys need a GL4 oil. Even regular motor oil, but not that thick stuff that goes in diffs.
Re: OK to use synthetic oil in trans and diff?
Posted: Sat Jan 25, 2025 3:46 am
by dutch
I just checked the oil can I used for my diff. Turned out to be GL4... I haven`t driven yet and I need to change out a seal which developed a leak. Would be wise to get GL5 I guess?
Re: OK to use synthetic oil in trans and diff?
Posted: Sat Jan 25, 2025 12:35 pm
by Mike W.
dutch wrote: Sat Jan 25, 2025 3:46 am
I just checked the oil can I used for my diff. Turned out to be GL4... I haven`t driven yet and I need to change out a seal which developed a leak. Would be wise to get GL5 I guess?
Yep, you really want GL5 in there. Not like you need to clean it out, but definitely a drain and fill.
Re: OK to use synthetic oil in trans and diff?
Posted: Sun Jan 26, 2025 5:06 am
by dutch
okidoki