Which diff oil weight: 75W or 140W?

[bmw540san]

I've done search here and elsewhere I have the conflicting info:

Liqui Moly website shows 140W and I tend to trust them as I've used their products for years now.

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Just bought my truck and it's on original fluids at 93K. Besides differentials, I'll change the transfer case fluid too.

I'll do some more research on the transmission fluid before I do it as we all know there are pros and cons of touching the fluid at these miles.

Thanks in advance for any info.

[TiAgX5]

I switched out the OE fluid at 100k miles, went with Mobil1 75w-90 syn.

No issues in the 80k miles after change, even with severe duty (towing 6000 lb trailers in temps exceeding 100 deg F).

[cn90]

I use Redline 75W90 and it is fine.
From what I understand 75W140 is used in heavy duty truck such as semi pulling a really heavy cargo load of 30,000 lbs etc.

You will be fine with 75W90.

[Ricky Bobby]

For 140W you better be hauling some serious cargo in a serious truck.

75W-90 is fine for our SAV's and most other utility vehicles, I used Redline 75W-90 as cn90 did

[TiAgX5]

Originally Posted by Ricky Bobby

For 140W you better be hauling some serious cargo in a serious truck.........

Or max loads in high temps.

I even hauled a 7500 lb boat/trailer, with 4 adult passengers and over 200lbs of luggage from northern PA to southern NJ shore in +100 deg heat.

Severe duty trip and 75w-90 was sufficent.

[LVP]

I did the Amsoil 75W-140 in my 328i diff due to it being a LSD. Otherwise, the recommended was the 75W-90 if I recall. The shop that flushed all my fluids put the 75W-140 in the X5 diffs. Looking at Amsoil's site now, the 90 is for std and the 140 for LSD. I think the 140 in a std diff is ok, but the other way around (90 in a LSD) is not.

[Ricky Bobby]

Considering our diffs are not LS units I'd say the 75w-90 is just fine

[bcredliner]

If the differentials and transfer cases have lasted long enough that I think it is a good idea to change them, why use anything different? How do I know what other fluids I use are better in this particular application.

[bmw540san]

Thanks to all of you guys. I'm more comfortable with 75W90 anyway and I'm using this one in my 5 series and I'll probably use it in X5.
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