Diff fluid change interval is 30k miles (15k for severe duty). 10 year interval, implies avg 3k miles per year. Suggest enjoy car more!

 

it only implies that as I remember it wasnt changed during that period. But yes it wasnt driven much more than 5k km annual ;-) And the fact that there was no stuff on the bolt means it was absolutely fine. Most advice for oil changes and so on are of course on an extremely safe side per the manufacturer (Although I dont recommend exceeding it people are way to conservative changing all the time even faster than what is suggested)

 

You are really overthinking something that doesn't matter that much, the diff and gears are not that sensitive to viscosity.
Get either 75w110 or 75W140 and move on with your life.

They don't even sell diff oil for our cars, so no I don't think they would.
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5w40 has been in the owners manual since day 1 as the optional viscosity for cold weather

 

so if it all doesnt matter that much. Why wouldnt you poor in the 75w90 stuff? (And why can a Corvette take 75w90 with much more hp and we shouldnt?)

In europe there is a liter of Honda sae90 diff oil available but too expensive for what you get.

I didnt know about the 5w40 being there from the start. I thought it was added later. Thanks for clarifying!

 

You could, its not going to blow your diff up on the street. But we know 75w90 is thinner than the original spec'd straight sae 90, so why would you?

 

fair question. I do have the 110 in right now. Just thinking if I should with the new diff since gasoline became the price of liquid gold here in Holland. Perhaps you are right and Im thinking too much.

I did read a post somewhere from a guy from OpieOils (or something similar) and he claimed that the 75w90 wasn't that much out of spec from the old straight 90 claiming there was no reason to go higher. And Torsen company says the thinner the oil the stronger the torsen function (they didnt mention a percentage of difference...)

 

Yes, I've read that too but can assure you our diff works fine with 75w140

 

Any idea if 90 vs140 has any serious impact on mpg?

 

Sorry, I cannot tell you that. I've never ran 90 in my current car and I don't pay attention to my MPG, plus I've been running 80w250 for years now.
I can say that going from 75w140 to 80w250 doesn't seem to be a huge impact. I still have roughly half a tank of gas by the time I arrive at the track when leaving my house with a full tank.

If you are that concerned with MPG then I would advice against 4.77s. You can use the money you save by not doing to buy more gas

 

The temp of my rear end didn't change(as far as I can remember, I did this back in 2010) going from 75/90 to 75/140. But the heat that our rear end creates is much greater than all the other cars I've had, I think because of how little gear lube it holds.
I know a lot of race cars that run in different series that have oil coolers for the third member to dissipate the heat so the gear lube doesn't thin out of a safe operating range. 477 gears will run hotter than 410 gears just driving down the road at speed. If you have been on here for years like some of us, you would have read about 100's of rear ends that have bit the dust. The thicker the gear lube the more cushion it gives to the shock of gear shifts or getting on and off the throttle.
As for gas mileage, I doubt you will find any measurable difference from the lube.

Food for thought, the rear end my 22,600 lbs motorhome towing a 4,000 lbs toad runs cooler than my S. But the rear end in my m/h holds around 3.5 to 4 gallons of gear lube. What does the S hold 1.5 or 1.6 pints.

Rod