Please help. 1988 chevy 1500 4x4, extended cab 8 foot boxes 350, L123 manual, Air conditioning. The cab gets a smell compared to hot 80w90 gear lube. This only happens when the windows are open so in the cold winter you never smell it. When you open the window(s) it smells like hot 80w90 gear lube, there are no other problems with this truck other than the smell. Please help?

 

So if it only happens when the windows are down and it smells like gear oil then I would suspect that there is oil from the transfer case or differentials getting slung onto the exhaust.

Have you crawled under the vehicle to see if there are any signs of lubricant being slung onto the body? Does the vehicle have any drips when parked?

 

There is nothing dripping on the exhaust pipe. I was wondering if this was coming from a breather on the transfer case.

 

Could be, the transfer case or one of the differentials could be building up pressure due to the breather being clogged. You might also want to check the fluid level in your transmission for good measure.