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Generator Oil

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I am planning to change the generator oil on our Onan 7000 (gas). It has approx 120 hours on it. The last change the shop used Onan 15W40 oil. I plan on using a major brand of oil, 15W40, but not Onan since I would have to drive about 40 miles from where I live to buy Onan oil. I do have an Onan filter which I will use.

However, I am wondering if I should change to a synthetic or a synthetic blend. We don't use the generator much but I do follow Onan's recommendations and exercise the generator monthly. Since all has worked well so far I probably will stick with just the regular oil but will appreciate comments on changing to synthetic or a blend.

Thanks,

RJ

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RJ, If you have a Cummins Dealer close you can get your oil there. When you exrecise your generator be sure and put a load on it such as the A/C. and turn off the A/C for a moment before shuting down the Gen.

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I use Mobil 1 semi synthetic 10w40 and it seems to work well. Stays pretty clean and I change it and filter every 150 hours or before winter storage since I usually don't use it for 150 hours during the year.

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No need to pay the extra for synthetic in my opinion. Just put a good (Delo) 15W40 in there and change it at the recommended intervals. Our generator is just about to roll over to 10,000 hours and it's worked pretty well for us!

We have been dry camping for the last 33 days running the generator about 10 hours per day (long story). We did an oil change in October and we will do one later this month after about 400 hours. No worries!

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I'm a true believer in using full synthetic, and on our (diesel) coach I use the same stuff (Shell Rotella T6 5W40 from WalMart) in both the engine and generator. We're only at 45,000 chassis miles and 1,600 generator hours, but no problems so far. I've had the pleasure of inspecting other engines I've owned during partial tear downs, and they've always been incredibly clean and measured very low wear. These have been gas engines, in which I run Mobil 1.

I figure that the cost of an engine rebuild on an Onan generator (particularly a diesel) is high enough to make full synthetic oil cheap insurance. But really, it just feels right.

Stan

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Make sure the viscosity of the oil conforms with both engine manufacturers specs for the ambient temperatures were you drive.

5-...... is lighter than recommended for most engines unless operated in Arctic conditions.

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The Onan Generator Handbook says

"Q: Can I use synthetic oil in my generator?

A: People use synthetic oils because the general opinion is that they can be left

in the engine longer than regular oil. However, if you decide to use synthetic oil

in your generator the maintenance time intervals given in the operator manuals

must still be followed."

The Handbook can be downloaded here http://www.cumminsonan.com/www/html/Common/pdf/rv/F-1123%20-RV-Generator-Handbook-2010.pdf

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There is no commercial diesel engine company, Cummins, Detroit, Cat, Max Force, that recommends useing a 5W-40 SAE oil in temperate north America. You are playing a dangerous game. Synthetic or not.

Also even at like viscosity a synthetic oil is thinner than it's counterpart regular oil. This particularly shows up when a hot high milage engine is idleing, with synthetic at idle the oil pressure might drop to 5 PSI lower than recommended, with regular oil also at idle the same engine would show 12-15 Psi on hot engine. More is better when oil pressure is minimal.

Admittedly the synthetic lubricates somewhat more efficiently, however the main advantage is it's ability to handle heat.

Most diesel pushers today with intercoolers barely get to 180 degrees, heat is not a problem.

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This is from the Onan RV Generator Handbook.

“Gasoline Engine Oil Quality – Use oil meeting any of the following API

Performance categories: SJ, SL or SM where SM is currently the highest quality

available. Look for the “Energy Conserving” designation to optimize fuel economy.”

NOTE: Multi-grade oils (such as SAE 15W-40) are recommended for year-round use in Cummins Onan

I highly recommend Mobil 1 full synthetic oil. You can use what ever viscosity you feel would be best for your application. I would use the 10-40 high mileage. It was developed for cars that have longer oil change intervals but can be changed to meet Onans recommendations and provide better protection.

Mobil 1 High Mileage 10W-40 synthetic motor oil meets or exceeds the requirements of:

ACEA A3/B3

API SN, SM, SL

Mobil 1 High Mileage 10W-40 is of the following quality level:

API CF

As you can see it meets or exceeds the requirements of the Onan Handbook.

Bill

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I just have to write a rebuttal to these statements.

“There is no commercial diesel engine company, Cummins, Detroit, Cat, Max Force, that recommends using 5W-40 SAE oil in temperate North America. You are playing a dangerous game. Synthetic or not.”

Engine manufactures recommend using oil that meets certain guide lines. Such as API CJ-4, CI-4 PLUS, CI-4, CH-4/ SM, SL, SJ. They often have a guide to viscosity.

I wasn’t able to copy and paste the Cummins chart that can be found on Quick Serve Service bulletin 3810340 04-DEC-2009 titled Cummins engine oil and oil analysis recommendations. The oil reconditions for 0 deg to 120+ was 0-40 5-40 15-40. The only restriction on synthetic was to use the same drain interval as regular oil.

“Also even at like viscosity a synthetic oil is thinner than it's counterpart regular oil. This particularly shows up when a hot high mileage engine is idling, with synthetic at idle the oil pressure might drop to 5 PSI lower than recommended, with regular oil also at idle the same engine would show 12-15 Psi on hot engine. More is better when oil pressure is minimal.”

When cold a 0-40 or 5-40 will flow faster but when at operating temperatures it will be a 40 weight oil and will show no difference in oil pressure. The fact that a 0-40 or 5-40 will flow faster when cold means it will be protecting your engine faster on start up when most wear occurs. I especially like the fact it gets to the turbo faster.

“Most diesel pushers today with intercoolers barely get to 180 degrees, heat is not a problem.”

The “intercooler” better called a charge air cooler is in front of the radiator and only cools the air from the turbo before it enters the engine to improve performance. It actually adds to the cooling load of the radiator. The diesel engine operates at much higher internal temps than a gas engine. It is only because they have much bigger cooling systems that they will run at the proper temperatures. You can do a search and find a large number of posts about coaches over heating. Most from dirty radiators. When I see EGT temps 1200 deg + when pulling a long hill I am glad I have oil that will stand up to it.

The oil today is not the oil of our youth. 50 years ago I would never run less than a strait 30 weight oil and never one of those new multi grade oils.

Bill

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