Did an Onan 4000 Gen oil change recently, and sampled the Mobil 1 0W-40 oil. This was about 14 months change interval vs 28 months for the previous change, Mobil 1 10W-40 High Mileage.Iron wear ticked up a bit, but ran the gen in some extra hot weather we had in the PNW this summer. Viscosity held up unlike the 10W-40 HM which sheared down.0W-40 definitely starts easier, but the 10W40 had less of the chug-chug when shutting down.Refilled with 0W-40.Column 2 is the 0W-40, Column 4 is the 10W-40 HM.

RambleOnNW,I commend you for having the oil tested. It's one of those things that I keep saying I'll do, but never get around to doing it.Looking at the numbers, the 0W-40 definitely looks like there are more particles in it than the 10W-40, especially considering it was only in half as long. Do you know how many hours were put on the oil in each case? That would be important information as you could easily have put more hours on the generator in the 14 months than the 28 months.Also, what weight oil does Onan recommend for your generator? On mine, I have found the recommended straight 30 weight works best unless we're camping in the winter, then I'll put a multiviscousity oil in it. Running the thinner oils during the summer, I have discovered that apparently the thinner oil sloshes around a bit more on hot days and the oil sensor will sometimes think the oil is low and shut the generator down if I hit a good bump. Haven't had the problem since using straight SAE 30.~Rick

A zero- XX weight oil in an air cooled engine??? Sorry, not on my watch. Guess I grew up working on too many air cooled engines (VW).

Rick Jay wrote:RambleOnNW,I commend you for having the oil tested. It's one of those things that I keep saying I'll do, but never get around to doing it.Looking at the numbers, the 0W-40 definitely looks like there are more particles in it than the 10W-40, especially considering it was only in half as long. Do you know how many hours were put on the oil in each case? That would be important information as you could easily have put more hours on the generator in the 14 months than the 28 months.Also, what weight oil does Onan recommend for your generator? On mine, I have found the recommended straight 30 weight works best unless we're camping in the winter, then I'll put a multiviscousity oil in it. Running the thinner oils during the summer, I have discovered that apparently the thinner oil sloshes around a bit more on hot days and the oil sensor will sometimes think the oil is low and shut the generator down if I hit a good bump. Haven't had the problem since using straight SAE 30.~RickRick,Good points, the wear metals are not much different than the last change nor the universal averages. Of the wear metals aluminum, chromium, iron, copper, lead, tin, nickel, manganese, silver, titanium, only iron (+3 ppm) and titanium (-3ppm) changed by more than 1ppm. The other elements are detergents or anti-wear metals.Total hours are about the same, 45 hours vs 42 hours.Recommended Onan weights are 30 weight, 15W-40, or 10W-30. We are out year-round so 30 weight or 15W-40 is too thick cold. 10W-30 is too thin hot. The previous synthetic 10W-40 HM seemed good but sheared significantly. Only possibility there is that it had something to do with being the first synthetic change after conventional 15W-40. 0W-40 is not a thin oil. It is thinner than 10W-30 or 30W at startup but thicker at medium and hot temperatures. Comparing against a 10W-30 Mobil Delvac heavy duty oil, the cSt numbers for 40C, 100C, and HTHS for 0W-40: 75, 13.5, 3.8 10W-30: 79, 11.9, 3.6. Mobil 1 10W-30 EP is thinner, 63.7, 10.2, 3.1. We use the 0W-40 synthetic in our cars also so always have it around.Ramble

wow...air cooled and there is no oil pump..splash system...keep posting...would like to know how long it stays together...I have the same unit

I'm sticking with 15W-40 in my Onan 5500.

Onan Gen Mobil 1 0W-40 vs 10W-40 HM Oil Analysis

wolfe10
Explorer
Oct 20, 2015
A zero- XX weight oil in an air cooled engine??? Sorry, not on my watch. Guess I grew up working on too many air cooled engines (VW).
Rick_Jay
Explorer II
Oct 20, 2015
RambleOnNW,

I commend you for having the oil tested. It's one of those things that I keep saying I'll do, but never get around to doing it.

Looking at the numbers, the 0W-40 definitely looks like there are more particles in it than the 10W-40, especially considering it was only in half as long. Do you know how many hours were put on the oil in each case? That would be important information as you could easily have put more hours on the generator in the 14 months than the 28 months.

Also, what weight oil does Onan recommend for your generator? On mine, I have found the recommended straight 30 weight works best unless we're camping in the winter, then I'll put a multiviscousity oil in it. Running the thinner oils during the summer, I have discovered that apparently the thinner oil sloshes around a bit more on hot days and the oil sensor will sometimes think the oil is low and shut the generator down if I hit a good bump. Haven't had the problem since using straight SAE 30.

~Rick

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Onan Gen Mobil 1 0W-40 vs 10W-40 HM Oil Analysis

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