Towing a LN2

[ekibike]

Interesting that overfilling led to overheat, as I'm equally naive what's the reason that happens?

My understanding is that the transfer case is supposed to be about half full to account for the expansion of the fluid when heated during driving.

 

[luthj]

When there is too much oil in a case with moving parts, the oil can't settle out after being agitated. All the extra gear contact results in the oil foaming and filling all the available space. Oil foam has a lot more viscosity than air, so you are basically putting drag on the rotating parts, which turns into heat.

 

[nathane]

Thanks luthj, much appreciated. Trying to get my head around why more oil (less air) leads to more foaming but I get that once you fill the box with foam it is a block to cooling. Thank you for the explanation.

 

[nathane]

On re-reading I think I understand. It's more that parts coverage leads to foaming rather than full enclosure preventing defoaming?

 

[luthj]

There are two approaches to Tcase lubrication. One is splash. A small mount of oil in the bottom of the case is splashed over the necessary parts. Gravity drains it back to the bottom.

The second approach uses a pump which draws from the low part of the case, and delivers the oil to the bearings, gears and chains are lubricated by the oil slung/splashed from the rotating parts.

When there is to much oil, it foams and fills the case (to much contact with spinning parts). Imagine trying to mix a pot of food, the more liquid in the pot, the harder it is to mix. This increase in effort (drag) means the liquid is stealing power/energy as fluid drag. Now imagine that you have gears spinning at hundreds of RPM, that power adds up quickly, and the Tcase will rapidly warm up.

Generally most of the rotating parts are not submerged. So they are moving through air with a bit of oil mist/droplets.

 

[nathane]

??