What weight should I use in my 1982 240D diff? I have some valvoline durablend 85w-140, and was wondering if it would be okay to use this oil.

Thanks.

I think 85W-90 or something of that order is what's called for...... I seriously doubt that the 85W-140 would damge anything, it just stays a little thicker as it warms up.

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1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

Mercedes has been specifying 90 weight oil for at least 20 years so I'd stick with it. 80w-90 or 85w-90, some use synthetic 75w-90. Gear lube is cheap so cost shouldn't even be a concern.

Just my $0.02,

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Brian Toscano

Dear rtykw2:

For all Mercedes cars, use only either 75W-90 or 80W-90 gear oil.
Even many big rigs use these weights.


Eric

I believe the -140 weights are used more for those that tow. Towing uphill in hot weather is the worst condition for differentials (that's how we test them). No harm in using it though.

Consider using full synthetic for the differential. There's a growing trend among auto manufacturers to use synthetic diff fluid as factory fill to get the EPA mileage ratings up. Little fluid is needed to fill the diff, synthetic only costs a bit more, and I understand the increase in gas mileage makes synthetic pay for itself, making it very attractive to use in the diff.

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95 E320 Cabriolet, 159K

The independant shop I go to (only MBz and BMW) use the 85-140 in all of the MBz diffs. Same shop and mechanic for 25 years.

Mobil 1, Gl-5, 75w-90. $6.99 will fill your diff. It's cheap and only changed every 30k, might as well use synthetic.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Dear prb51:

It's all because your indie did not read MB factory manuals.

Yes, putting 85W-140 in a MB car's differential unit does not cause any problem but it's not necessary at all. In fact, it will cause a drop in gas mileage due to the much thicker gear oil.

Many big rigs use Mobil 1 75W-90 (yes only 75W-90) synthetic gear oil, and change it every 500,000 Kmiles. The fluid still comes out clear.

Eric

There was a bmw TSB from not too long ago stating that in all their LSDs a 75w-140 'XJ' lube be used (its actually a german cstrol product). The reason for that was becasue the LSDs in particular were noisy, exhibitng a bit of a whine (my 91's LSD does this). Using the 75w-140 should have no problems at all, and is more or less interchangable with the 90, as I am confident BMW researched it thuroughly before releasing a blanket TSB. By the way, synthetics typically protect better, so there MAY be more leeway to use a heavier lube and swap like they did when using synth oils. Dino oils are typically more friction-inducing, and may be less interchangable..

Remember, 90wt gear oil is the same viscosity as a heavy 40wt to a light to mid 50 wt engine oil. a 140 gear oil is probably liek a 70wt engine oil's viscosity. However the flow dynamics are substanitally different.

Some people claim they see a difference between heavy and light gear oils, in MPG terms. The same can be said with heavy and light motor oils. However, a LOT of people go from light to heavy and don't see any difference in MPG. Same for when doing oil analyses of these fluids.

So much of a lube oil's protection is based upon the additive package these days. Just use a quality oil and youll be fine, especially in a diff.

I didnt notice any difference when I tried 75w-140 in my bmw LSD as compared to when I had 75w-90 redline in it.

But as a rule, the owners manual should be your first reference for fluid specs and weights. aftger seeing lots of oil analyses and researching the topic thuroughly, I have found that very little if any is gained by changing from oem spec to a heavier lube.

Unless your diff is getting noisy, in which case a heavier lube can often help, if you dont wish to make the necessary repairs or replacement.

JMH

JMH

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (116k)
1991 350SD (206k)
1991 300D (228k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (267k)

Past Diesels:
1983 300D (228K), 1985 300D (233K), 1993 300D 2.5T (338k), 1993 300SD (291k)

Eric, Could be due to my location in Arizona - 100+ days not uncommon. They read/know the MBz rec.

Yes, the 85w-140 may be there for the hot climate. The big rig fleet owners are very sensitive to mileage issues, hence the use of synthetic 75w-90.

I'm not a big proponent of synthetic lubricants, but the differential is the first place where synthetics make a significant difference and should be used.

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95 E320 Cabriolet, 159K

This may have changed, but the last I the list, Mercedes has approved no synthetic oils for their differentials, nor is any 140 weight oil approved for any applications.

Len

Len,

I haven't seen synthetic gear lube or ATF (for older trannys) on the approved sheet. However, there no reported failures that I'm aware (however, that doesn't mean there aren't any!) The approved list in MY opinion is marketing with some engineering added. Companies must pay MB to test their product and if passes the tests, then its added to the list.

On the other hand, MB has only approved SAE 90. I do not think they've ever listed any other viscosity, regardless of ambient temperatures. I personally use Valvoline 80w-90 in my differential and don't worry about it.

In my Dodge 3/4 pick-up with a Dana 70, both 80w-90 and 85w-140 are specified depending on ambient temperatures.

In any case, GL-5 gear lube MUST be used. GL-1 thru GL-4 are NOT rated for differentials (but GL-4 is specified for many manual gearboxes).

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Brian Toscano