0W20 In Heavy Duty Diesels?

[mechman600]

Originally Posted by RobertISaar

i too am an active BITOG'er and would like for everybody to get the best of what their money is paying for. 10 and 15W oils are old-school thinking, there's no reason any engine running a 30, 40 or 50 weight oil can't run 0W-30/40/50, or at least 5W-30/40/50.

From what I understand from scouring the BITOG site (mind you, not too vigorously, as it bores me a bit), 5W40 oil starts off as a 5W oil and then stuff is added to get the 40W when hot. As oil ages and starts shearing, this additive stops doing its job and oil gets thinner and thinner when hot.

I could be wrong.

With this understanding (or lack thereof) I always wonder after how many miles does shearing start to have a significant effect - within the recommended oil change interval? If so, that's not good, and a reason I would shy away from lower weight oils.

[RobertISaar]

you're somewhat correct, but that's oversimplifying it a lot.

the more "multigrade" an oil is, the more potential it has for shearing down, but that doesn't mean that it will. this is the reason all of the hardcore BITOG guys do oil analyses when changing to a new oil, to see how far they can go on them before running into the viscosity changing too much.

also, 5 weight vs 5W or 40W vs 40 weight are very different. 5 "weight" is implying viscosity when warm, 5 "W" is implying viscosity when cold. just something to keep in mind.

as for your explanation of stuff being added, that's correct. the base oils are engineered to be very thin, then viscosity index improvers are added to slow down the rate of thinning when the oil gets heated up. this allows for you to have an oil that is thinner when cold and thicker when hot compared to a single-grade oil. the drawback is shearing will bring it closer to a single-grade oil as it ages. there are two opposing forces at work here though, shearing and mass loss. shearing takes the part of the oil that would make it thicker and degrades it's ability to keep the oil thick at higher temperatures. mass loss is the "phenomenon" that occurs where the lightest parts of the oil burn off at higher temps, causing the oil that doesn't burn off to be thicker.

the rate of shearing vs mass loss will determine what viscosity the oil will be at any one time. considering a lot of the BITOG guys go ~10,000 miles or more on an oil change, something has to be working well.

[tjts1]

0w30? Not in my diesel.

[oil pan 4]

Originally Posted by RobertISaar

you realize that when the oil is up to full temp the 0/5/10/15/20W rating is of no importance, right? that specification is for when the oil is cold, the second half of the rating is viscosity at 212*F.

Yeah that is why I would not switch from an XXw-30 or XXw-40 to a 0w-20 weight oil. I don't care for or need the 0w part of the oil and do not want the 20 part of the oil in my engine.
If I was in Maine I might test an 0w-30 or 0w-40 oil for winter use only.

[RobertISaar]

5w-xx is as low as im going to go, I barely get 10psi with the engine warmed up.

seemed as if you were putting emphasis on the 5W portion of the oil rating as being responsible for low pressure at full temp.

in any case, 20 weight is something i would personally leave to lighter duty engines without doing some significant testing on an engine i could afford to lose.