If 0-30, 5-30 and 10-30 oils protect so well, why do we need 'high mileage oils'?? We've established that they're different in one way or another, so are the oil companies simply telling us that the 'standard-issue' oils are inadequate???
Some of the high mileage oils I've seen are not rated "Energy Conserving." They must give up that fuel savings for additional viscosity so they're at the high end of the viscosity range, and they may also have some extra seal swelling agents.
30 wt. ranges from 9.3 cSt to 12.4 cSt viscosity, so there is quite a range. The lower end will give some fuel savings and the upper end may result in less oil leaking past worn or sticky rings and seals.
When a car gets up in mileage, the seals start to leak and the rings wear...and the owner notices he has to add oil between changes. This bothers a lot of people. This high mileage oil costs almost twice as much as regular oil, but is thicker and has ingredients that apprantly help tired seals do their job. I have read quite a few reports that say just using one of these high mileage oils completely eliminated the need to add oil or eliminated leaks. If this is true, it certainly is worth the price.
I have a car with worn or sticking rings. Using 5W30 or 10W30 (the recommended oil), I was using a quart every 850 miles. I switched to 10W40 GTX high mileage. Usage went to 1 quart every 1,050 miles. In my case, I don't think it is worth it. A standard 10W40 would probably have done almost as good.
