[The_otherM235i]

Hey everyone, currently running the stock bmw oil in my rear diff, saw on ECS they sell liquid molly diff oil and was thinking of swapping it quickly. How much fluid fits in the diff? Is it as simple as dropping the plug and refilling it?


Was gonna use liquid molly Hupoid gear oil 85w -90 as its meant for track use witch I do.



Thanks guys!

[JD11937]

Originally Posted by The_otherM235i

Hey everyone, currently running the stock bmw oil in my rear diff, saw on ECS they sell liquid molly diff oil and was thinking of swapping it quickly. How much fluid fits in the diff? Is it as simple as dropping the plug and refilling it?


Was gonna use liquid molly Hupoid gear oil 85w -90 as its meant for track use witch I do.



Thanks guys!

I have an M240xi and use redline products, they have a solid reputation and know of many other highly modified cars that use the same. Not sure if specs are the same. That said I use liquimoly oil and think they are a great company. Probably can't go wrong with either.

On the M240xi we don't have drain plugs only fill plugs which makes the process more difficult. You need a pump to suck the old oil out and then to refill it. Your car is probably the same. You just slowly fill it until it starts to leak out of the fill plug.

[4Hockey4]

Same here, Redline. Pump out, pump in...almost 2 quarts I believe.

[aerobod]

Originally Posted by The_otherM235i

Hey everyone, currently running the stock bmw oil in my rear diff, saw on ECS they sell liquid molly diff oil and was thinking of swapping it quickly. How much fluid fits in the diff? Is it as simple as dropping the plug and refilling it?


Was gonna use liquid molly Hupoid gear oil 85w -90 as its meant for track use witch I do.



Thanks guys!

Typically if a 75w90 diff oil is specified, you would want to go to a 75w110 or 75w140 for track use, as an 85w90 would be thicker when cold (and hence problematic in the winter), but would have the same viscosity at 100C as the 75w90 oil.

75w140 oils at 120C have a similar viscosity to 75w90 oils at 100C and with some cars you may see diff oil temps up to 130 or 140C on the track.

Be aware oils such as Redline No-Shock range compared with the normal range with LSD additives or NS range without LSD additives may cause problems due to the grease-like polymer additives.

[The_otherM235i]

Originally Posted by aerobod

Typically if a 75w90 diff oil is specified, you would want to go to a 75w110 or 75w140 for track use, as an 85w90 would be thicker when cold (and hence problematic in the winter), but would have the same viscosity at 100C as the 75w90 oil.

75w140 oils at 120C have a similar viscosity to 75w90 oils at 100C and with some cars you may see diff oil temps up to 130 or 140C on the track.

Be aware oils such as Redline No-Shock range compared with the normal range with LSD additives or NS range without LSD additives may cause problems due to the grease-like polymer additives.

I ordered liqui molly Full synthetic 75w90 GL5 that said it's for the "track" only other option is red line 75w110 gl5. Should I go with that instead?

[aerobod]

Originally Posted by The_otherM235i

I ordered liqui molly Full synthetic 75w90 GL5 that said it's for the "track" only other option is red line 75w110 gl5. Should I go with that instead?

Depends on what diff temperature you are seeing on the track, anything under 100C and the 75w90 is fine. Have to put temperature strips on the casing or use and infrared thermometer to determine. If the car is stock power and you don't have an LSD fitted, it shouldn't get too hot. Also depends on how long you run, the ambient temperature and the times between sessions to allow the diff to cool down. 20 mins of hard running every hour lets the diff cools quite a bit.

[The_otherM235i]

Originally Posted by aerobod

Depends on what diff temperature you are seeing on the track, anything under 100C and the 75w90 is fine. Have to put temperature strips on the casing or use and infrared thermometer to determine. If the car is stock power and you don't have an LSD fitted, it shouldn't get too hot.

My car is far from stock and im quite experienced and push while on the track. I always knew the diff got really hot but while on the track with 30c days it could probably benefit from this higher temp stuff. It's non-lsd

[aerobod]

Originally Posted by The_otherM235i

My car is far from stock and im quite experienced and push while on the track. I always knew the diff got really hot but while on the track with 30c days it could probably benefit from this higher temp stuff. It's non-lsd

Without an LSD I'd be surprised if it got above 100C, as there aren't any clutch plates to heat up, just the relatively low frictional losses from the gears meshing. In normal use the diff will only be at 50 or 60C in 30C ambients. Difficult to tell what oil to use without a temperature reading immediately after coming off the track, then add 10C or so to allow for the cool down lap before the exit.

[dradernh]

Originally Posted by aerobod

Without an LSD I'd be surprised if it got above 100C, as there aren't any clutch plates to heat up, just the relatively low frictional losses from the gears meshing.

Same for a geared LSD like the Wavetrac?

[aerobod]

Originally Posted by dradernh

Same for a geared LSD like the Wavetrac?

Should be somewhere in between due to more meshing surfaces, but no friction plates.

[HP Autosport]

Originally Posted by The_otherM235i

Hey everyone, currently running the stock bmw oil in my rear diff, saw on ECS they sell liquid molly diff oil and was thinking of swapping it quickly. How much fluid fits in the diff? Is it as simple as dropping the plug and refilling it?


Was gonna use liquid molly Hupoid gear oil 85w -90 as its meant for track use witch I do.



Thanks guys!

Open diff? We use Redline 75W90. Fill it until it starts to trickle out of the filler hole.