Debate: Should you use synthetic oil in older engines or not? Here's what I found out

I was reading through some old service bulletins from the 90s and found out that some early 4.0 liter Jeep engines actually had issues with synthetic oil causing seal leaks. I always thought synthetic was better no matter what. But then I talked to a guy at a shop in Phoenix who said he runs conventional in anything pre-2000 because the seals are just too old. On the other hand, my buddy swears by synthetic in his 89 F150 and has 300k miles with no drips. So which side are you on? Has anyone else seen real damage from switching to synthetic on a high-mileage motor?

2 comments

2 Comments

kelly.daniel2d ago

Have you tried running high-mileage conventional for a few changes before switching to synthetic?

nathan_hill602d ago

It's like a lot of things in life, people replace stuff because it's new and shiny and forget that sometimes the old stuff just works fine for what it is. That shop guy in Phoenix probably just saves himself a headache by sticking with what he knows.