JImbo1

Thanks Haulin...I wonder how hot oil has to be to reach its boiling point?

P Kennedy

Standard petroleum oil starts to breakdown at the 260F range while synhtetic is closer to 400F. Tractor trailer rearends will run as high as 240F continously when pulling in the mountains with B-trains (140,000 Gross). Outside temps and loads will affect gear oil temps, that is why different oils have different purposes. The pressure applied to gear surfaces are a lot higher than what a bearing experiences under normal conditions. PK

JImbo1

I had the rear end drained and cleaned

When I checked the synthetic oil I put in a month ago, it was dark.


Does anyone think this is normal or was the rear end so hot that it turned the oil dark?

P Kennedy

Oil analysis will tell you what the truth is about your oil and if it is bothering you change it. Look for silvery particles not gold colored (LSD) as this could be bearing failure. PK

JImbo1

I've been thinking...If you can't put your hand on the oil pan on the bottom of your engine after a long haul...then why should you be able to put your hand on the rear end, especially when these 18 wheelers get to 240 degrees, perhaps that's the nature of the beast and they are supposed to get hot.

I don't think it ever gets 240, of course, I didn't get the temp, but if it was ever 240 degrees I think I would get an instant burn.

y-knot

My rear end oil (grease, as some call it) stays very clean, I do use AMSOIL series 2000 75W-140, it comes with a blue tint, and looks the same when it's changed. It's hard to smell if it's burned or not because on how strongly rear lub smells. I think if you are as worried about this "problem" as you seam to be, I'd invest in a MAG-HYTEC cover and get a guage to monitor it. My rear end temp says pretty much at 140-150, and it doesn't appear to be influenced by out side temps, of coarse in the winter it stays cooler, and takes a long trip to warm-up.