I swapped to a full synthetic 5W-40 and my old 7.3 Powerstroke started puking oil past the rear main seal at 215,000 miles

Everyone online swears by Rotella T6 for these old 7.3s, saying syn oil is the only way to go. I ran conventional 15W-40 for the 8 years I've owned this truck and it never leaked a drop. Two weeks ago I did an oil change with the T6 5W-40 and within three days I had a puddle under the bellhousing. The thinner stuff just found every weak spot in those 23 year old seals. I dropped the pan and replaced the rear main, but now I'm wondering if I should just go back to conventional for the high pressure oil pump and injectors. Has anyone else had syn oil cause unexpected leaks on a high mileage HEUI engine?

3 comments

3 Comments

jana_jones1mo ago

Yikes, that’s a rough break. I mean, it’s frustrating when you do the “right” thing everyone swears by and it backfires like that. Maybe it’s just me but I’ve heard of that happening on older trucks with high miles, the thinner oil just finds the path of least resistance. I’d honestly go back to the conventional 15W-40 if it were my truck, especially since that’s what kept it happy for eight years.

lilyp371mo ago

Oh man, been there done that with my own old beater truck lol. Sometimes I think my engine just gets offended when I try to change up its oil routine!

michaeld481mo ago

Well T6 is actually a 5W-40 not a straight 5W-30, so it's not as thin as you're thinking.