Quote:
Originally Posted by ConnClark
So my car manual says I should use 85w-90 gl4+ differential fluid in my front and rear differentials. I decided to switch to 75w-90 GL5 synthetic.
According to this I should be good on protection and pick up a 0.5% fuel economy gain.
https://www.fleetequipmentmag.com/sk...nner-gear-oil/
Any thoughts? |
Yes, as the page says, there's nothing wrong with that. 75w90 just flows better when cold than 85w90 does. Both oils reach the same viscosity range when hot, so there's no damage being done.
Just don't go under the Xw90 range, unless you're doing it for a very short time to clean out a filthy differential, like I once did. The old oil had seen 180,000+ miles, 18 years, and it was filthy. I thought I should clean the filthy oil out, so I ran on two batches of 5w30 in a 75w140 differential, but I did it for only about 5 miles. Even then, I saw a few metal shavings in the oil, so cheap 10w40 would probably be better.