Why use higher viscosity differential fluid?
 

I am going to be replacing the differential fluid on several of my cars using Mobil 1 75w90 synthetic. However, I've noticed that some instead opt for Mobil 1 75w140. What's the case to be made for the higher viscosity fluid? What are the advantages and disadvantages?

In this area I'm a "lube newb"....just want to benefit from others' experience.

Thanks.

You will receive no less than 1,000 different opinions on this topic...

In general, heavier viscosity index (VI) lubricants, gear oils in this case, provide more protection for heavily loaded gearsets. I also think that the 75w140 may (possibly) be a little quieter.

In my 116.120 I used Mobil 1 75w140 in the 2.47:1 axle swap. It's a good lube and provides extended drain intervals...FWIW

This was my reasoning on going with a heavier VI oil in the 190's differential, to try to quiet its whining down. Helped a little bit...

Just what is the change interval on diff oil on these cars?

I'm not aware of any official MB interval. FWIW Kent Bergsma recommends every 60-80k or five years, whichever comes first.

So no hesitation in deviating from MB recommendation?

Hmm I either read somewhere or jinned up 100k intervals..

I also read that when you change your diff oil it can bring out the whining noises...Not sure if thats just shop legend or anything like that...

I'm not sure of the MBZ spec, but I change diff lubes at 50,000 miles...

I doubt it. We had a customer once did a DIY service and put ATF in the diff of a 115 MBZ and drove it that way for years before anyone discovered it....never made noise.

I doubt it too. Seemed like nothing more than urban legend.

I've got a thread around here somewhere with the maintenance sheets from MB..

Aha

http://www.peachparts.com/shopforum/tech-help/284333-maintenance-system-sheet.html

Links don't work for me.

Yeah looks like the hosting site I used deleted them! I'll fix em and put a link in a sec here

My 92 was first done at 150k....am doing again at 245k. 91 at 108k and 90 at 95k have never been done AFAIK.

I located the maintenance sheets....I don't see an interval for differential fluid.

I was also wondering how much additional fluid I might be able to get out with a fluid extractor.

I change brake fluid twice a year in all our cars, except the 116 which has DOT 5 silicone (which I never change), oil and filter every 6,000, service the 722.120 every 40,000, change the ATF in my 2001 Mustang's Tremec 3650 5 Speed every 20,000 and diff lube at 40,000 to 50,000, regardless of any MBZ, BMW or Ford service suggestions....