does synthetic gear lube resist expansion due to heat better than regular gear lube?

 

I don't know the answer, but most fluids don't expand much with heat.

But why would you worry about the expansion? Typically there is a lot of air space lef tover when you fill the differential, plus most have a vent to let out the air as the air expands and contracts.

I wouldn't worry about the expansion. The more important question is how well does the oil protect the drivetrain. Follow SAE/API specs and you should be fine, whatever you use.

Jim Henderson

 

This issue just came up in talks with a friend of mine. Todd drives his own semi for a living. A few days back he ran into a situation with a fellow trucker that has us both puzzled. The other guy was having a big problem: seems his gear box was "expelling" gear lube out the vent at the reat of about a gallon in 100-150 miles. They drained the gear box of the fully synthetic gear oil and replaced with conventional. No more problems....
Subsequently, they were told that synthetic gear oil can expand as much as 40% when hot. 40% !?!?!? That seems like an awful lot to me! But, in this particular case, switching from synthetic to conventional corrected the problem at hand.
Can anyone confirm this information - or disinformation - about 40% expansion????
Thanks,
Brian

 

That is exactly the problem i'm having. Although i'm not losing quite that much fluid, its enough to leave a puddle when i park. It only happens when its hot. It is currently filled with regular gear lube. What would you all do if you were me, change gear lube and fill with regular or synthetic? Thanks guys


Ryan

 

>This issue just came up in talks with a friend of mine. Todd
>drives his own semi for a living. A few days back he ran
>into a situation with a fellow trucker that has us both
>puzzled. The other guy was having a big problem: seems his
>gear box was "expelling" gear lube out the vent at the reat
>of about a gallon in 100-150 miles. They drained the gear
>box of the fully synthetic gear oil and replaced with
>conventional. No more problems....
>Subsequently, they were told that synthetic gear oil can
>expand as much as 40% when hot. 40% !?!?!? That seems like
>an awful lot to me! But, in this particular case, switching
>from synthetic to conventional corrected the problem at
>hand.
>Can anyone confirm this information - or disinformation -
>about 40% expansion????
>Thanks,
>Brian

Was this guy running the straight 50wt synthetic or a multi-weight in the gearbox? I've heard of Heavy Truck transmissions pressuring up, but not due to oil expansion. One of my Eaton 18 speeds had an O-ring go bad in the splitter, and the gearbox pressured up with air(I'm sure you know alot of the systems on semis run off of air) 40% seems real strange. Let us know what else you find out...........I'm real curious now.

 

Ryan: my first move would be suspect a mechanical problem. Is there a problem (bearing?) causing the oil to overheat and expand? Is the oil foaming? Is gear box being overfilled? I can't imagine a design that would be expected to produce the problem you are seeing. Please respond with solution if you come up with one.
Deezil: I'm gonn talk to my buddy some more and run your comments by him. While it is not a direct concern for me, I'm puzzled by this and want to try and come up with a resonable answer (or two).
Thanks,
Brian A

 

Everything is mechanicaly good. All new bearings, all gears within specs, and the fluid isn't overfilled. Thats why this is so puzzling. Thanks for any more ideas.

Ryan