It’s fairly safe to say, that if your manual calls for 75w85 & 80w90 and you’re changing the fluid on a reasonable basis, that yes, you can use pretty much whichever one you & your wallet fancy.
Only the BITOG set probably even knows it is there and has some form of lube in it.
But it may make a difference to guys with hot hatch's with small AWD rear diffs with semi high to high HP/TQ going through them. AND the small bearing taking the load in them. Or people that use smaller vehicles that tow.
whether that lab is willing to share the results or not, do you think they would share the names of all the 75w85 and 75w90 (and maybe even 75w110 and 75w140) they have tested? I don’t know if you ever found a Valvoline test, and I would love to see a Motorcraft 75w85 test. So yes, I would love to see results, but if we knew which fluids were available, it might help us focus on which to press for reports on.
Let me reach out and see if they will share all those results. Not sure what’s been tested; but understand we’re asking for a LOT of “free” data they’re not getting paid for. I’ll see what I can do… no promises, but definitely hoping (for all our sakes!) that we can get that data!
Unless the Ford fluid is fully synthetic (and Group IV/V choices at that), there’s no way it “flows better when really cold”. I’m no gear oil expert by any means, but I believe the Brookfield number is the one that matters in this case. If it makes you feel any more secure in this choice, even @High Performance Lubricants has said Amsoil makes some pretty good gear lubes, and the testing shows Amsoil turns in really good wear numbers on the 4-ball wear tests, and good performance on the weld test as well.
Class 8 trucks recommend 75w90?
I didn't say that, but since you asked, yes some do for cold wx ops.
"Diff Life CC" is HPL's Cold Climate Differential Life gear oil, you won't find that on shelves. But it can be on your doorstep in 2 days!
From your excellent addition, you can also see how the weld test is conducted; rather than a 40kg load, it is raised much higher... in the chart, you can see some oils fail at 400kg load on the weld test, and some fail at 500kg. David said an easy way to compare the load is 40kg (4-ball wear) represents "daily driving", city acceleration in traffic, per se. Weld test represents drag racing, with high shock loading.
They aren’t sealed and oxidation does occur
), KV100 is 11.53, spec grav .87, -40 Brookfield 48,000, pourpoint -49, ~65% “synthetic” base, ~35% “additives.