oil 75000 mileage
 

Why do some oils like snythetic add new leaks to an engine? What is the difference in the 75,000 mile oil we see on the market now? Is it thicker in its viscosity?

additives...something to reinvigorate the seals, etc...

Bill

Yes Mobile makes a High mileage 75,000 miles or more oil that says on the 5 quart container synthetic partial with means of letting less oil pass through gaskets . It works and they are telling us 100 synthetic oil does not affect gasket porosity.My 77 vette leaked oil with Mobil 1 and with Mobil high mileage has stopped almost completly. My other car will use a quart of oil in a 20 mile round trip and none with high milage Mobil . Read the back label they have a compairson chart !

THey dont add leaks, the syn is a smaller molecule or so they say and finds its way through places the conventional may not.
If it leaks it was there the whole time. I swore off syn oils, prefer the better cushion the conventional oil gives. 180k and doesnt skip a beat, cheap oil changes are a plus. Still use a good wix filter though.