Manaz
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Not sure why 0w40 is not recomended???
Here's the best "simple" explanation I've yet found for multigrade oil nomenclature (it's from the UK Mobil 1 site):
What is oil viscosity and what impact does this have?
Viscosity is a measure of the resistance of a fluid’s flow. The thicker (high viscosity) of an oil, the slower it will flow.
Most oils on the shelves today are "Multigrades", which simply means that the oil falls into two viscosity grades (i.e. 10W-40 etc). In a 10W-40 for example the 10W bit (W = winter) simply means that the oil must have a certain maximum viscosity or flow at low temperature. The lower the "W" number the better the oil's cold temperature performance.
The 40 in a 10W-40 simply means that the oil must fall within certain viscosity limits at 100°C. This is a fixed limit and all oils that end in 40 must achieve these limits. Once again the lower the number, the thinner the oil: for example, a 30 oil is thinner than a 40 oil at 100°C.
Just be careful when reading their explanation of the winter weight - what it should really say is that the lower the number, the more flow there is at low temperature - more flow is not necessarily better, as it may lead to insufficient "coating" at cold temperatures (which is where you really do want oil to cling to your engine components, until the oil pump's really going properly). It's sometimes advantageous to run a thicker oil on an older engine as well (as it's less likely to bypass rings/etc and be consumed when the engine is cold).