Oil thins out when it is hot, right? So when you start your engine the oil is cold and thick, right? So shouldn't oil read 30w10 as it thins out when it heats up? In reality it is the other way around kind of
. Can someone explain this?
Because multigrade oils are a new technology, relatively speaking.quote:
Originally posted by turbochem:
I see what you're saying.....why is it when the oil is cold, and thicker than when warm, do they give it a lower number??
Yes (5.5 times as thick by my math).quote:
Originally posted by Ken4:
Does this mean the oil is 5 times thicker @ 40C?
I don't think you're reading the chart correctly.quote:
Originally posted by Ken4:
But according to this:
http://www.bobistheoilguy.com/visc.html
80cSt @ 40C is thinner than 14.5cSt @100C.
I am confused.
80cSt @ 40C = 9.4 cSt @ 100C = SAE 20 ???quote:
Originally posted by G-Man II:
I don't think you're reading the chart correctly.
Actually, all oils (even straight grades) that meet modern API requirements have an "additive package" comprised of detergents, dispersants, and extreme pressured compounds. Multi-vis oils have an additional additive, the VI improver. (However, some synthetics may not have this if the base oil blend itself has a sufficiently high VI to cover the desired vis spread.)quote:
Originally posted by Problem Solver:
Multi-vis oils, whether petro or synth, were designed to have much better pumpability in the winter, thus the lower number on the front-end (5w-30, the "w" stands for winter); the additive package is such that it makes dry start-ups less abrasive on your engine. On the flip-side to that, what they mean by "30" is that under heat and stress the oil will perform like a 30 weight not that it truly is a 30; this sounds a lot like the post up above by "MPH". Multi-vis oils require an additive package, some are more extensive than others, however, you should be looking for an oil with a high TBN and minimal additives; you want your engine protected by the base oil and not the additive package, afterall, the additive package is the first to boil off.
On this chart, yes. BUT, that doesn't mean that every oil that has a vis of 9.4 cSt @ 100°C will have a vis of 80 cSt @ 40°C. That isn't what the chart is trying to show.quote:
Originally posted by Ken4:
80cSt @ 40C = 9.4 cSt @ 100C = SAE 20 ???quote:
Originally posted by G-Man II:
I don't think you're reading the chart correctly.
Exactly. You will never fully grok the meaning of "double-you" until you give up the notion that the left number of the multi-vis rating bears any relationship to the right number.quote:
Originally posted by turbochem:
I guess they could have used letters instead.....
That's why when I was a kid, and someone tried to explain multi weught oils to me they said something like "Well, when it heats up, it gets thicker." Obviously that 30 being higher than 10 threw their reasoning a bit off....the oil is not thicker at high than at low temps.....quote:
Exactly. You will never fully grok the meaning of "double-you" until you give up the notion that the left number of the multi-vis rating bears any relationship to the right number.
Except for gravy!quote:
Originally posted by Dr. T:
Yes, oil thins out when hot...as does every other liquid.