Black Tranny oil……….

I checked my plow trucks tranny oil before I started plowing, and after. After plowing for 17 hours, the fluid went from red to black. The transmission is working perfect, could this be the lockup clutch slipping? I plow in low range, let it shift through the gears, and never use OD.

It still shifts solid, and doesn't slip.

I also haven't changed the fluid this year yet, was going to get to it this weekend, after the plowing is done. Is there a chance that this is old crap laying around from the summer sitting?

Kinda worried about my plow truck tranny, it is my livelihood.
Author: TK