My( very limited) understanding is that a 0w/40 oil protects better at both higher and lower temperatures than a 5/30 or 10/40 oil. Is that correct?
Maybe.
Oil is naturally thicker at lower temperatures. In the old days, oil used to be monograde, so you'd go out and buy a 40 viscosity oil. It would be like treacle at room temperature and quite fluid at running temperature (say 100 degrees C for argument's sake).
Such an oil was OK ish for cars of the time, but a modern engine won't cope with oil like treacle because the clearances between the mechanical parts won't allow adequate oil flow when cold, and the engine will be damaged at cold start.
So, all modern engine oils are "multigrade" in that their grade changes with temperature. This means we have effectively a much thinner "base" oil, but it's made thicker at high temperatures by viscosity improvers (VIs). In layman's terms, a 10W40 oil can be considered to behave like a 10 viscosity oil at low temperature (the so-called "winter" rating - hence 10w) and a 40 viscosity at high temperature.
So, a 0w40 is different to a 10w40 in that it's thinner at low temperatures and about the same at operating temperature. You will have a thinner oil at cold start and this might help it circulate earlier and save some engine wear at startup, so this is indeed a possible benefit to choosing this oil. Probably the only possible benefit unless you're going to leave it in there for 20k and take a chance on its' long life! I can't see how a 0w40 would be different to a 10w40 when hot, although if you really do cook the oil, maybe Mobil 1 would survive better. You won't do that in an Omega that sees road use, though.
Remember that a multigrade oil is made out of a very thin base oil with VIs added to thicken it up. VIs lose their effectiveness over the life of the oil, so the oil could become too thin where it's important (at full working temperature) with age. A 0w40 will rely more on VIs than a 10w40, as it will have a thinner base oil. Being a quality fully synthetic oil the Mobil will probably have good quality VIs that last well, but a warning not to trust poor quality oils that have a wide spread of winter-to-hot rating.
Of course, all this theory is meaningless unless you can see inside the engine and watch the oil working - we can't!
We can only perhaps wonder about the effects of oil when stripping engines for repair - hence my post that modern engines really don't wear that significantly, so oil choice is not a big issue. Whatever oil you choose, barring a catastrophic failure, your car bodywork will have rotted away before the engine wears out anyway.
Kevin
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Topic: Fully synthetic engine oil ?. (Read 5040 times)