The MB (dealer) 85w90 has 50% higher shear strength than the Mobil 1 75w90 at 40C.
40C is the typical operating temperature of a differential in most conditions.
75w90 = 99 cSt @40C
85w90 = 153 cSt @40C
If you have to ask, higher value is better.
The viscosity trends downward and both are equal at 100C, however 100C isn't a temperature the differential will ever see.
MB as of the latest guidance in the W211 does NOT want the 75w90 used especially in the Diesel applications...for obvious reasons (torque).
I am going with Drivbiwire on this. I am aware of the Mercedes bulletin that says the new
spec lube can be used, but in the ML and the E500 all diffs have been changed to the MB branded 85w90.
With 4000+ lb vehicles I would rather have the protection than the minute
fuel economy increase which was the primary reason MB put out the bulletin for the thinner lube.
Are we going to sing the old song with new tunes?
I will not argue about anything, I will present the facts and please, before you guys start winning read everything in those pictures.
MB prefills all E class cars w/following gear sizes (look at the picture) with synthetic fill-for life, universal hypoid gear oil, SAE 75W-85 since 04.11.2001 and this oil is made by Fuchs Europe, MB part # A 001 989 33 03
. This oil is on MB 235.7 Rear axle gear oils (Specification 235.7)
plus Fuchs TITAN SINTOPOID FE 75W-85
and Mobilube FE 75W-85
. How comes this can be install in M, R and G class in both axels? They also have high torque engines. Page 13 from Factory Approved Service Products.
I look through all gear oil Spec sheets three times and I was not able to locate MB Hypoid Gear Oil (85W-90) MB Part No. A 001 989 17 03 10
. Maybe MB is phasing it out (Mercedes-Benz Specifications for Operating Fluids (MB BeVo
) web info is been updated on 09.14.2011).
Mercedes-Benz Specifications for Operating Fluids: Overview Sheets
But I pay attention to the outdated Factory Approved Service Products August 2007
which I download from STAR TekInfo web page, dated there 06.05.2008. and I notice number three after the “Recommended” oil MB Hypoid Gear Oil (85W-90)ᵌ
, and what this small tree means: ᵌMeets sheet 235.7 specification.
And my head is spinning now: how come 85W-90 is better than 75W-85, but meets same specs? Is it MB going to flush millions down the drain because they factory fill most of the cars w/75W-85 when they face all the warranty claims for differential repair? Alternatively, 75W-85 maybe offers same protection like 85W-90, or vice versa.
Let us look at the Fuchs 75W-85 specs vs. Mobil1 75W90. Which one has higher shear strength at 40⁰C? And Mobil1 [email protected]
⁰C is 106, not 99. There is also Fuchs 75W-90 which gets into big rig (Scania, Iveco, Mack, MAN) differentials and it has higher shear strength than 75W-85. But those don’t make that much torque, only around 1500 lbf-ft at 1200 rpm, and they don’t haul much weight, only between 35 000 to 120 000 pounds all day long.
I would like to get one of those 40⁰C differential, because apparently mine is running little bit hot, if I remember almost burn my hand on it when I change the fluid and if it’s available running w/o cooling system engine too.
Tolerances into the differentials are very small; otherwise gears will get damaged easily, so all the friction when power is transferred to the wheels (change in torque direction) create lots of heat.