Switched to synthetic gear oil and saw a 15 degree temp drop in 6 months

Been running the same 18 speed Eaton Fuller in my Pete for about 4 years now. Always used conventional 80w90 and had to baby it on long grades during summer. Switched to a full synthetic 75w90 last winter and after 6 months of hauling I'm seeing transmission temps drop 15 to 20 degrees on the same runs from Portland to Spokane. The shifting feels smoother too especially when cold. Anyone else notice a real difference going synthetic in their transmissions?

3 comments

3 Comments

the_miles3d ago

Buddy of mine saw 10 degrees cooler after switching, but then his rear main started seeping.

patricia323d ago

Yeah I saw a report from a trucking magazine that tested synthetic in heavy duty transmissions. They claimed the heat reduction was mostly from less internal friction. Makes sense because conventional oil gets churned up more when its hot. I switched my older 13 speed to synthetic about a year back and the cold morning shifts are night and day. No more waiting 5 minutes for the oil to warm up before I can get it into gear. The temp drop is real too, I saw about 12 degrees on a pretty flat run out of Denver.

charlies373d ago

I mean, I hear what you're saying about those cold morning shifts being easier, and I'm not gonna argue that part. But the heat reduction thing, I'm just not sold on it being that clear cut. I ran conventional in my old 13 speed for years, then tried synthetic for about six months, and on the same routes out of Denver I only saw maybe 4 or 5 degrees difference at most. Maybe it's just me, but I think a lot of that 12 degree drop could be from other stuff like ambient temp or even how hard you were pushing the truck that day. I've also heard from a few mechanic buddies that synthetic can actually make some older seals leak more, so I'm kinda wary of it unless you know your trans was built for it. Not saying you're wrong, just that my experience didn't match up that neatly.