Tried a synthetic blend gear oil instead of full synthetic in my old Jeep last weekend and now the transmission shifts smoother at 140k miles

I figured the cheaper oil would cause more noise or slipping, but the thicker base actually tightened up the syncros in my 1999 Cherokee - has anyone else seen better results stepping down to a blend in high mileage transmissions?

4 comments

4 Comments

bailey.jennifer1d ago

You mentioned the thicker base tightening the syncros, but I really think that's just the fresh oil making things feel better for a little while.

kimw571d ago

Oh man, fresh oil always feels like a magic trick at first. But that thicker base in a blend can legit help worn syncros grip better, especially in an older Jeep. I had a 2000 Wrangler that got quieter and shifted nicer after I switched to a blend at around 130k miles. It's not a permanent fix, but it bought me two more years of smooth driving before I finally had to rebuild the trans.

colethomas12h ago

Wait, didn't you read that article from one of the Jeep forums about how thicker oil actually changes the clearance between worn syncros? I swear I saw a write-up where a guy measured the gap before and after switching to a heavier blend. It's not just in your head, the extra viscosity literally fills in some of the space that's been worn away. That's why the effect lasts for a while instead of disappearing after a day or two. Fresh oil alone would just feel smooth for a weekend then go back to grinding, but a blend with that thicker base keeps the syncros engaged longer. I've heard guys say it's like adding a temporary spacer without pulling the trans apart. So yeah, I think there's more to it than just the new stuff feeling nice.

olivia_white9312h ago

I ran thicker oil in my old YJ for almost two years and it shifted way smoother.