Likely the higher amounts of detergents. A high mileage synthetic oil with seal swellers would be more appropriate.[emoji106] I've had that happen too.
Ive got to side with Terry on synthetic oil for break-in......
I believe in the U.S. synthetic oil came on strong much later than elsewhere in the world. In fact there was even litigation with Castrol about what really is synthetic oil, as there was no standard of ingredients. Castrol was getting away with calling oil with lower base stocks synthetic, and they got into hot water for that, one reason reason Castrol lost credibility and market share here. I believe our standard of what synthetic oil is still lower that that of European countries. Obviously to meet certain requirements the oil hast to be pretty good like the 0W oils and 5w 30 oils. The wider the range normally the higher the synthetic content viscosity modifiers.[emoji111]
Likely something else going on IMHO, it should make zero difference.[emoji111]
The old school GTX was good stuff, at one time it had loads of zinc "not as much now"[emoji17] I've gotten 200,000+ on engines running that oil, still don't burn a drop and are smooth as could be.
I'm not 100% sure if that was seal swell, or just the detergent in the synthetic oil washing away the gunk. Now as far as I can remember most American made cars leaked oil at the time regardless of the oil used.[emoji16]
Well it's a 5.4 and still running so you're still ahead?[emoji6] No no the 2v were fine, the 3v were ticking time bombs and require synthetic oil do to the small oil passages and cam phasers. My brother found that out the hard way.[emoji51]
I have a by-pass oil filter in my Duramax. So I spend $25 and get the analysis done. I run Mobil 1 Turbo Diesel. I only change oil once yearly. I was doing about 15k a year for miles...
