Originally Posted by Triple_Se7en
That's interesting and informative..... thanks!
It drove me nuts trying to figure it out at the time until I saw the Starburst. In the old F-150 before the rebuild and reseal, I would run 15w-40 in the summer, then 5w-30 MaxLife in the winter. Ordinary 5w-30 would leak out way too fast. With 15w-40, the leaking slowed sufficiently that I didn't have to add over an OCI. MaxLife 5w-30 made it so I didn't have to add over the OCI, either, and that was when MaxLife wasn't ILSAC rated. I switched to Mobil Super 2000 5w-30 (our HM variant at the time, a blend, and it was ILSAC rated). It leaked again like a sieve, and I was adding. I went back to MaxLife, and things were back to "normal."
I'd gather the MaxLife had higher HTHS when it wasn't ILSAC rated, versus ILSAC rated HM oils, and it's possible that seal conditioning agents might be at a different level. Of course, since then, I've never been terribly excited about having an ILSAC rated HM oil, and the only one I really thought was a good idea was the dexos1 MaxLife, since that had potential as possibly the best priced dexos1 oil readily available.