I recently heard the owner/mechanic & his main mechanic @ a British Automotive specialty Indy shop claim this for older cars such as my 2000 Jaguar XJ8. He said they will leak oil if use synthetic bc it can seep out of smaller gaps in the seals vs. conventional oil.Don’t believe I have ever heard someone try to claim conventional oil is better than synthetic in at least 20 years.
I had an oil pan leak, very small. My 1st ever oil leak in this car & I had changed oil & filter myself for > 15 years on that car. 1st few I let the dealer & then a couple Indy shops do it & was not happy with their work or the $$$. I did extensive searches & found absolutely nothing to back up this claim. Why did I not have a drop of oil leak in the ~ 18 prior years using synthetic oil if it was so bad for my car?
I dropped the oil pan & changed the gasket with a genuine Jaguar gasket & changed to Mobil 1 5w-30 full synthetic for older (>75k miles) engines. It took a few weeks but, the oil leak was gone/fixed. I suspect I did not need to change that oil pan gasket. Leak was probably coming from somewhere above. B4 changing the gasket, I checked all around that pan & saw no evidence of a leak there or anywhere else. I replaced the gasket bc that was what this expert said was leaking.
Anyway, I am a believer in synthetic oil.
I change oil 1x/yr. well under 10K miles.
I can understand the temptation for DIY owners to change oil & filter every 3k or 5K miles bc it is relatively easy & makes them feel better. Some send old oil in for analysis.
I wonder if they get routine medical labs; CBC, Lipid panel, Fasting Glucose, etc., every 3 months despite being healthy? Do they get a colonoscopy every year just to be on the safe side & remain healty?