Synthetic Gear Lube

[daniel3507]

I know it calls for 80w or 90w which is conventional but why can you not use synthetic? I have Amsoil 80w-90 in now and have had no problems but am getting my 4.10's installed soon and was wondering if I should stick with that or go to a conventional

 

[exbass94]

I know it calls for 80w or 90w which is conventional but why can you not use synthetic?

Who ever said you CAN'T use synthetic? If you have synthetic, go ahead and pour it in.

 

[daniel3507]

I just figured since it had to be since it calls for 80w or 90w and all i have seen in that is conventional

 

[exbass94]

Conventional typically comes in 80w-90, whereas synthetic is usually 75w-90. They're almost the same thing. The second number (90) is the important number. That's how thick it is at operating temp. The first number is how thick it is below freezing temps. Synthetic doesn't thicken up as much in cold weather, hence the lower first number. My axle also calls for 80w-90 and I've been using 75w-90 with no problems.

If you're getting new gears installed, I would probably use conventional at first, and drain it out after 1-2k miles. When new gears break in, they create a lot metal shavings that end up in the oil. After getting that break-in crap out of there, then start with the synthetic.

 

[daniel3507]

If you're getting new gears installed, I would probably use conventional at first, and drain it out after 1-2k miles. When new gears break in, they create a lot metal shavings that end up in the oil. After getting that break-in crap out of there, then start with the synthetic.

Thats a good idea. I never even thought of a break in time.

 

[Hahnsb2]

The only time I'd recommend against synthetic is if you have a Powertrax No-Slip, I've seen how it behaves with synthetic in a friends Ranger and have heard other bad handling reports about using synthetic with them. I just stuck conventional in my Dakota with the No-Slip and it's been great.