When to worry about engine noises?
Not 100% up on Rotella any more, but using a diesel formulated oil in a gasoline engine is very bad policy.
I agree. The American Petroleum Institute (API) has standards to which oils must meet in order to be certified to said standard. There are other standards out there but API is probably the most well known. For diesel engines the standards start with the letter "C" followed by a letter. They started with CA and as a new standard was created, the next was CB so on and so forth. For gasoline engines the standards start with "S". The newer the standard, they higher in the alphabet the second letter is. A quick look at a bottle of Costo's 5W-30 shows it is certified SP, SN. Generally speaking, the newer will supercede the lower specs but that can be misleading. I had a difficult time finding the API specs for Rotella online but if you look at the bottle, you should see API then CK, CJ or something like that (those are the diesel specs. You
may see an "S" spec but the one I found online did NOT have an "S" rating, meaning it does NOT meet an automotive spec and you would be in violation of any new car warranty out there I would be willing to bet. To clarify, some oils may have both a C(x) and a S(x) rating, meaning it is good for either diesel or gas engine.
So what are the characteristics which the specs are written for? There are several properties of oil that are looked at. Viscosity index: change in viscosity over temperature. Pour point: lowest temperature it will pour. Flash point: Lowest temperature at which vapors will ignite for a short time. Fire point: Lowest temperature vapors will continually burn. Oxidation: Resistance to the oil oxidizing or turning to varnish. Corrosion: Resistance to rusting of parts. There are a few others that I just can't recall the name to off hand but one has to do with electrolysis between dissimilar metals, resistance to high pressure breakdown and a few others.
I have heard of engine rebuilders recommending Rotella before but I do not know why. If your engine has a flat tappet cam I would recommend an oil with ZDDP additive which is a zinc compound that takes the place of lead which was used as a lubricant back in the old days and probably why my parents told me not to eat snow (each flake has a particle of dirt in it to which it forms). That said there are ZDDP additives you can add to oil however I recall a lubrication class I took years ago they had told us that oils can only mix with approximately 30% by volume additives (super saturated) and that if you add an additive to an oil that it possibly would not combine but rather remain separated...I can not confirm or deny this as the truth but it has always stuck in my brain. I have added ZDDP to oil nevertheless.
