Has anyone put 10-40 in the front diff.? I am getting ready for winter and currently have 20-50 dino oil in it. I just put Mobil 1 MX4T 10-40 (Syn.) in the motor and thought that since winter is here, (It just snowed today), that I would try this in the front diff.
Does anyone think this is to light of an oil for the front diff?

 

Not too thin! I run Mobil 1 Vtwin year round. Synthetic is a good thing.[img]i/expressions/face-icon-small-wink.gif[/img][img]i/expressions/face-icon-small-smile.gif[/img][img]i/expressions/face-icon-small-shocked.gif[/img]

 

650freak, it's too thin. 10w40 synth will loosen your diff up a lot. I use 20w50 synth and it is still a touch thin. Less locking torque.

I used 20w50 dino oil in the front diff, and it made the steering much harder in the cold.

I suggest not using 10w40 synthetic in the front diff, since at the temperature the diff operates at, 10w40 synth is extremely less viscous than 10w40 dino, 5w30 dino etc. At engine temps, the viscosities of the synth and dino oils are probably a lot closer. But at cooler temps, you have to use a much thicker synthetic weight to get the same affect on the diff lock as the dino oil.

I do not have any lab results on viscosity tests, but let me tell you what I believe:
20w50 Synthetic is the thinnest synth you should think about in the front diff. I know for a fact, that the diff is less stiff with 20w50 synth than with the stock oil in it. I don't believe it will hurt the diff, just won't lock as well, nor be as stiff when it's not locked. I might try a ?w70 synthetic in it.

10w40 Dino oil is the thickest dino oil you should use in the front in the winter. IMO. Your 20w50 was probably working just great all summer. But in the coldest weather, your steering will be a bear.

Kawi says you can use stiff oil in the front diff. I'm not saying you can't. I am just saying that you are thinking about putting some extremely thin oil in there. Also, you have some pretty thick oil there too.

I am going to play around withg synthetic viscosities more in the front diff, since I don't want the viscosity variation you get with dino oil, but I want it stiff than with 20w50 synth.

 

Oh yeah, Dangerous is right about the synthetic oil in the engine. It's great stuff. I use MX4T in the engine. I strongly believe synth is right for the front diff, just try to find some thicker stuff.

The diff doesn't heat up like the engine, so it's harder to compare engine oil weights from dino to synthetic. I don't know the exact answer.