We're not on the same wavelength here.

You're simply stating the advantages of synthetics...It goes without saying that synthetics are superior lubricants...based on robustness to heat, film strength, purity, stability, "flowability"... etc.

What I'm pointing out is that 50 weight oil is not light. It is heavy.

Motor oil thins as it heats and thickens as it cools, right?

Accordingly, an oil is rated for one viscosity when cold, and another when hot, right?

The measurements are taken at specific temperatures: Precisely, at 0? F (the first number) and at 212? F (the second number), right? (BTW, the W means the oil meets specifications for viscosity at 0 F and is therefore suitable for W(inter) use. It is written after the first number, not the second.)

So, as an example, 0W-40 oil has less viscosity when COLD than does 10W-40. 10W-40 oil has less viscosity when COLD and HOT than does 20W-50. Right?

At the low-temperature end, the first number ( the ô10Wö in 10W-40 ), oil has to be resistant to thickening so that it flows more easily to all the moving parts in your engine. This is particularly important at cold start. Right?

Once the engine is running, the oil heats up. Right? Now, the second number in the viscosity rating--the "40" in 10W-40, for example--tells you that the oil will stay thicker at high temperatures than one with a lower second number--the "30" in 10W-30, for example. Right?

The more resistant it is to thinning, the higher the second number (10W-40 versus 10W-30, for example) and that's good. Right?

Well, within reason. Thicker oil generally seals better and maintains a better film of lubrication between moving parts.

To lubricate the engine the oil must be delivered to the engine by the oil pump, right?. But, if the oil pump encounters too much resistance to flow the pump opens a relief valve and vents the oil back to the inlet... so 50 weight oil will show a slightly higher pressure on the gauge but is it looking after the engine better?

Factory spec. 10W-30 oil will be able to flow more easily throughout the engine at a lower pressure but greater volume. One of the oil's jobs is as a coolant, so large flow rates are favorable, right? In different climates, and in different Japanese engines, it is not uncommon to hear of heavy oils bulging oil filters as the oil pump can't dump enough oil through it's relief valve fast enough.

It goes back to what I said previously. The engine is hot. It's under load. You give it the boot. Load on the engine increases as the RPM climbs. The engine is spinning fast now. It needs lubrication as measured by volume now. In this instant, of greatest need, can the oil pump get thicker 50 weight oil out through all those low tolerance nooks and crannies in the engine? Number 1 cylinder, farthest from the pump...is it being starved of lubricant when it needs it most?

What was the problem cylinder in the Isuzu gasoline engines...?



What's really important is that you use the oil viscosity your car's owner's manual recommends.

--Bighorn--