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

Here's a couple of low and high temp graphs of viscosity in cSt of the oils mentioned. You can make your own here.

I plan to stick with the 0W-40 and am showing great results. 3ppm increase in iron is really not significant.

Looks like great results to me too. There is not one thing here to point to and say this oil is not working here. The iron is low, and the difference is probably below the noise level. On a splash lubed engine with no oil filter. I have this oil around the house anyway and it is an excellent choice for the Onan.

SRockwood wrote:

tpi wrote:
Thanks for the report! A week ago I did oil change with Mobil 1 0W40. The one minor concern I have is shearing and good to see it is holding up.

One thing I've meant to do and will is dip the crankcase with thermometer and check oil temperatures more frequently. Especially during extended runs in 100+ degree weather. One time I did after about 45 minutes powering my roof air in 80 degree weather measured about 175. My friend has a larger twin cylinder Onan we dipped after an extended highway drive in 100 degree weather powering two roof airs. Oil temp was 235-240. Airflow through his Onan may or may not be optimum.

I certainly think the 0W40 is perfectly suitable for the Onan provided oil temperatures are not getting out of hand. The vehicles and conditions it is rated for are very demanding. And this report bears it out. However I will watch oil temps more carefully and if the Onan is generating oil temps frequently in the 245-to 300F (Harley Vtwin) range I'd be open to go to XW50 oils. I cannot see any reason why this 0W40 would be inferior to any 30 weight in this application-as it remained a 40 weight in the report.

I use the RV four seasons and encounter 20 degrees F or lower. For sake of starter and starter drive I prefer to have the engine spin over as easily as possible. Still maintaining protection in hot weather.

Thinner oils generally stay cooler though, so you may be robbing Peter to pay Paul here.

Yes and I highly doubt the oil temps will rise high enough to warrant the 20W50. But curiosity is there. These are low specific output engines with fan forced ventilation. Not like a Harley idling in parade on hot day-or pulling hard up a hill with a tailwind. FWIW on my 880 Sportster I've only seen 210 degree oil in the hottest weather (but not in the very worst possible conditions).

Good comments by all, thanks.

I plan to stick with the 0W-40 and am showing great results. 3ppm increase in iron is really not significant. We run Mobil 1 in our cars and the iron results are at or below the universal averages.

0W-40 is a good compromise for me, thicker than 10W-30 yet thinner than 15W-40. Most wear happens at cold start and I don't expect a splash lubed motor to be any different. I'd expect the 0W-40 to more readily splash cold. I see that in the start up behavior, the gen stops shuddering faster after cold starts with 0W-40 than the other oils I used.

I thought the 10W-40 HM synthetic would be optimal but it did start harder at freezing. The shearing cause is unknown but may be related to being the first change after conventional oil and was affected by dissolving the remnants of the conventional oil. The 100C viscosity at 10.55 was still above the starting viscosity of typical 10W-30 of 10.2-10.4.

tpi wrote:
Thanks for the report! A week ago I did oil change with Mobil 1 0W40. The one minor concern I have is shearing and good to see it is holding up.

One thing I've meant to do and will is dip the crankcase with thermometer and check oil temperatures more frequently. Especially during extended runs in 100+ degree weather. One time I did after about 45 minutes powering my roof air in 80 degree weather measured about 175. My friend has a larger twin cylinder Onan we dipped after an extended highway drive in 100 degree weather powering two roof airs. Oil temp was 235-240. Airflow through his Onan may or may not be optimum.

I certainly think the 0W40 is perfectly suitable for the Onan provided oil temperatures are not getting out of hand. The vehicles and conditions it is rated for are very demanding. And this report bears it out. However I will watch oil temps more carefully and if the Onan is generating oil temps frequently in the 245-to 300F (Harley Vtwin) range I'd be open to go to XW50 oils. I cannot see any reason why this 0W40 would be inferior to any 30 weight in this application-as it remained a 40 weight in the report.

I use the RV four seasons and encounter 20 degrees F or lower. For sake of starter and starter drive I prefer to have the engine spin over as easily as possible. Still maintaining protection in hot weather.

Thinner oils generally stay cooler though, so you may be robbing Peter to pay Paul here.

Thanks for the report! A week ago I did oil change with Mobil 1 0W40. The one minor concern I have is shearing and good to see it is holding up.

One thing I've meant to do and will is dip the crankcase with thermometer and check oil temperatures more frequently. Especially during extended runs in 100+ degree weather. One time I did after about 45 minutes powering my roof air in 80 degree weather measured about 175. My friend has a larger twin cylinder Onan we dipped after an extended highway drive in 100 degree weather powering two roof airs. Oil temp was 235-240. Airflow through his Onan may or may not be optimum.

I certainly think the 0W40 is perfectly suitable for the Onan provided oil temperatures are not getting out of hand. The vehicles and conditions it is rated for are very demanding. And this report bears it out. However I will watch oil temps more carefully and if the Onan is generating oil temps frequently in the 245-to 300F (Harley Vtwin) range I'd be open to go to XW50 oils. I cannot see any reason why this 0W40 would be inferior to any 30 weight in this application-as it remained a 40 weight in the report.

I use the RV four seasons and encounter 20 degrees F or lower. For sake of starter and starter drive I prefer to have the engine spin over as easily as possible. Still maintaining protection in hot weather.

Ramble,

Thanks for posting your OA results... Double thanks for having more than one reference point by providing two results. Triple thanks for doing a generator.

Spent several hours mulling the results and what they may or may not mean to me.

It seems odd that a Mobil product would shear out of specification. If I understand your data, the oil was sampled in 2014 but was installed about 28 months before. Sometime in late 2012? It is possible that being of that vintage, there was something a bit different in the formulation due to it's manufacture date, SAE requirements OR because it was a High Mileage oil. Still, to shear out raises questions. But, I suspect that there are millions of engines of all stripes running billions of hours on slightly out of spec. oil.

That said, some oils do start as a '40' or '30' for example and with use do shear down to a 'light 40 or heavy 30'. You get the idea. Nevertheless, it doesn't look like any harm has been done based on the results of the second OA.

IME, having performed OAs on my different vehicles (using different oils over the years) I have found that Mobil products tend toward increased iron levels. Don't know why, but there's tons of iron in an engine so it's of no consequence unless it goes off the charts. Just saying, high Fe is typical of Mobil products in my experience.

Using a XERO W40 doesn't appear to have caused any harm at this point. But, it is 'early' with only 40 some hours of use. While I use 0W20/30 oils here in Texas and now 5W30 in the Sprinter diesel, their low cold viscosity is rather meaningless in a climate that rarely dips to 32.... maybe sometimes into the teens. But these are water cooled gassers. A 5W20/30 would work just as well.

Air cooled jobs may require a bit more thought. After looking at the oil requirements for my Onans over the years, I settled on the OEM recommendation of 15W40 OnaMax. My reasoning is this: 15W will take me down to about 15F (-10C) that is good enough for my purpose. I'm not going RVing in sub-freezing weather. Likely, not even in near freezing weather!!! On the other hand, at oil temperatures below 100C (~212F) the oil does not achieve its 'summer' weight of 40. So, the multi-vis 15W40 should provide low temperature start up; less viscosity as it warms to 100C; and then stabilize around the necessary 40 weight when it's cooking. So, for me, going to protective levels below those where you routinely use the generator doesn't seem to have any positive effects. Neither does it appear, based on your OA, to have any negative effect at low engine hours.

I don't think a 0W/5W provides any warm up ability due to its thinner viscosity. How fast the oil warms up depends on how much heat you are putting into to the oil; how quick you are doing that heating; and the quantity of oil you are heating. An Onan with 1.5L capacity will warm up a hell of a lot faster than my Sprinter diesel with 12.5 L in the crank case. Thinner oil would not seem to make a significant difference in warm up with such a small motor.

Another factor I considered is the location of my generators: under the RV, in a box, inside a box, behind the rear duals. On a Texas day, the road temps are amazingly hot and more so behind and under a working RV. It's going to be hotter than the hubs on a hell wagon inside the Onan box, inside the compartment, under the RV. So, at least a 40 for sufficient protection all year round.

Thanks for the OAs. Good work!

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

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

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.

~Rick

Rick,

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