failure to start

[inanecathode]

I thought that oil started out thinner and thickened up with heat. That is why they came out with dual weight oil, because it was hard to start an engine when it was cold, so they made the oil thinner at cooler temps, which is the reason that everybody thinks it is not good to rev a cold engine.

I've never thought thought that it was bad to do this. Are you implying that oil is not everywhere in the engine yet, and there is metal on metal contact, or is it some other reason.

A 'cold start' where there is no oil in the engine is damaging to every engine, so I always add an oil additive that makes it cling to metal. Lucas oil if you're familiar with it.

I dont know how they figure it, but i've drained cold oil and hot oil. Hot oil's thinner.

[QBS]

Cold engines may not have oil in all their important, but not pressure fed, nooks and cranies.  Cold engine parts have different sizes than hot engine parts.

[Rick G]

The polymers in  the oil thicken up (add cushion)  you won't see it when draining the oil.

[inanecathode]

No, it thins out at higher temperatures, the numbers are based on viscosity not, uh, 'cusionability'.
The W doesnt stand for weight, it stands for winter, it's how easily it flows when it's at colder and colder temperatures (0w must flow better at -40c than 5w at -30c).
Oil doesn't thicken as it warms up, it thins, the 'multi viscosity' refers to how drastically it thins. Imagine cooking oil, when its cold it's basically solid, but when you heat it up it flows as easily as water, that's single viscosity. Motor oil doesnt do this due to the additive packages (cept single viscosity, but noone uses that anymore). The two numbers in the descriptor of the oil have little to do with eachother as far as operating temperatures go. One is rated on 'flowability' at varying low temperatures, one is rated at 'flowability' at 100c.
0w-30: Flows great at cold temperatures, ends up kinda thin at operating temperature
10w-40: Flows slower at cold temperatures, thicker than 0w-30 at operating temperature
20w-50: Flows terribly at cold temperatures, much thicker than 30 at operating temperature.

[Jimustanguitar]

I thought it was the other way around, so that oil was thinner and thus made an engine easier to start at colder temps... I'll have to look it up on Wiki now 'cuz I'm confused.

Very interesting, thanks.