A good read on oil

motorpirate said

Probably over my head a little then...
I do know this though, when my shop started getting into law enforcement fleet accounts the Crown Vic's were having a LOT of main bearing thrust issues on the then new 5W30 oil.
I mean like converter bolts hitting the back of the block in drive!!
Most got mains under warranty by the local Ford dealers who was using the 5W30 as it was what ford called for. They were using Valvoline.
We at the time were using Castrol. We put 10W40 in cars of any Department that would let us ( some had warranty concerns) and Castrol 5W30 in those that insisted.
We had NO main bearing failures on any car that had the Castrol, and over a few years took on most of the local agency's as word in the industry was cars we serviced didn't have engine falures like the ones being serviced at the local dealers and county garages.
So, I kind of have a soft spot for Castrol I guess...

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I've seen many cases like this.

One issue is the grade into which an oil falls is rather wide. You can test 3 oils and one will be built in the low end of the grade, one might be in the middle and the last one on the high side of the grade.

Also, I forget the exact testing procedure, but the oil being tested needs to be "in grade" for a certain number of tests. So let's say out of ten tests on any particular oil, if that oil passed the grade test 5 times out of 10 it's considered in grade.

If an oil is built on the low side of its grade, and it starts getting some load on it, like at the thrust or exhaust valves or whatever, it will get hot enough that it falls out of grade. And then the oil can't get rid of the heat that's pushing it out of grade, so the parts get hotter and the cycle continues.

It's almost impossible to get all the information from the oil manufacturers. The only real way to know if an oil is capable is to test it. And that costs big $$$$$. And it takes time.

Or, you learn the way you did, which isn't cheap either.