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Old 03-19-2011, 07:29 PM   #1
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Synthetic in Onan 5500 HG JAB

I called Onan the other day and was told NOT to use synthetic oil in my 2005 Onan 5500 Marquis Gen. with 300 hrs on it. He didn't know why...just said don't use it. It's hard for me to believe that a good quality, full synthetic oil would not be good for ANY gas engine. I know that Onan wants you to use their own oil for obvious reasons, but I guess I'm just stupid or something.

Can anyone tell me why I really SHOULDN'T use synthetic in my gen.

Bill
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Old 03-19-2011, 09:07 PM   #2
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I don't see any reason not to use synthetic either, except maybe cost. You can use any oil that meets the service spec, which will be some viscosity, e.g. 10W30 and API service classification, e.g. SH or SL.

Current Onan gas gensets specify API SH, SJ or SG and SAE 30 if over 32 degrees or 15W40 if 0-100 degrees. 10w30 is allowed if temps are in the range of 0-80.

http://www.cumminsonan.com/www/html/...s/983-0101.pdf
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Old 03-20-2011, 03:53 AM   #3
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i changed my oil when i first got the moho with about 49 hrs on the genny. i installed amsoil 10w30 synthetic oil. i have put about 25 hrs on it with no problems. it has not used any oil.
my onan 5.5 holds exactly 2 qts of oil with a filter change. i had to start it and leak check it and shut it off before i could put the balance of the second qt in the crankcase.
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Old 03-20-2011, 06:34 AM   #4
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FYI Shell Rotella T meets Onan's specs.
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Old 03-20-2011, 09:10 AM   #5
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The reason Onan tells you not to use synthetic is that most of them are not available in the correct weight and have lowered levels of ZDDP additive required to meet the new API SL requirements that only apply to gasoline motor vehicle engine oils.

Shell Rotella T6 Synthetic is a 5W40 and will meet all the requirements for your air cooled Onan and has the higher level of anti-wear additives desired by Onan. It also meets the API requirements but does not have to lower the zinc levels as its primarily diesel engine oil.

By the way, 10w30 is only for use in the Onan air cooled gen sets if the ambient tems STAY consistantly below 80degF. If its below 80, why would you be running the gen set under load, you surely don't need AC.

Just use the recommended 5W40 syn or 15w40 conventional diesel engine oil, not the 10w30.
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Old 03-20-2011, 12:22 PM   #6
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Quote:
Originally Posted by WSRG View Post
I called Onan the other day and was told NOT to use synthetic oil in my 2005 Onan 5500 Marquis Gen. with 300 hrs on it. He didn't know why...just said don't use it. It's hard for me to believe that a good quality, full synthetic oil would not be good for ANY gas engine. I know that Onan wants you to use their own oil for obvious reasons, but I guess I'm just stupid or something.

Can anyone tell me why I really SHOULDN'T use synthetic in my gen.

Bill
I changed the oil/filter in my 5.5KW Onan 2 days ago. It had 549 hours. I used 10W 30 as usual. I finally bought a end cap style wrench. The one that was in the manual bag is too big and even this one is a mite big. I had to put a piece of paper towel as a shim. Works fine.

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Old 03-20-2011, 02:17 PM   #7
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Originally Posted by jcthorne View Post
The reason Onan tells you not to use synthetic is that most of them are not available in the correct weight and have lowered levels of ZDDP additive required to meet the new API SL requirements that only apply to gasoline motor vehicle engine oils.

Shell Rotella T6 Synthetic is a 5W40 and will meet all the requirements for your air cooled Onan and has the higher level of anti-wear additives desired by Onan. It also meets the API requirements but does not have to lower the zinc levels as its primarily diesel engine oil.

By the way, 10w30 is only for use in the Onan air cooled gen sets if the ambient tems STAY consistantly below 80degF. If its below 80, why would you be running the gen set under load, you surely don't need AC.

Just use the recommended 5W40 syn or 15w40 conventional diesel engine oil, not the 10w30.
Genset should be run at 1/2 load or better at least once a month or you'll be buying new carb $180.00 bucks,because these carbs are throw aways.If you check your owners manual you should see it under exercise genset.
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Old 03-20-2011, 06:44 PM   #8
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You SHOULD use a good real synthetic oil. I and many others use Amsoil products.
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Old 03-21-2011, 12:56 PM   #9
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The WORST thing I ever did to my old Emerald 6.5 in our previous coach was replace the OEM carb with an Onan replacment. The OEM was made in mexico the replacement, although in an Onan box, was a cheap chinese copy that never worked correctly. I tore it down several times to replace parts that did not fit, or work as designed but it NEVER ran right. Even the Onan tech I paid $140/hr to tune it could not make it run right. Thier answer? buy another carb and try again.....

Keep the OEM carb and rebuild it. Do NOT buy the chinese replacement.
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Old 03-21-2011, 01:41 PM   #10
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T Even the Onan tech I paid $140/hr to tune it could not make it run right. Thier answer? buy another carb and try again.....

Keep the OEM carb and rebuild it. Do NOT buy the chinese replacement.
That's got to be infuriating
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Old 03-21-2011, 05:30 PM   #11
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The WORST thing I ever did to my old Emerald 6.5 in our previous coach was replace the OEM carb with an Onan replacment. The OEM was made in mexico the replacement, although in an Onan box, was a cheap chinese copy that never worked correctly. I tore it down several times to replace parts that did not fit, or work as designed but it NEVER ran right. Even the Onan tech I paid $140/hr to tune it could not make it run right. Thier answer? buy another carb and try again.....

Keep the OEM carb and rebuild it. Do NOT buy the chinese replacement.
Marquis Gold 5.5,6.5 and 7000 series gensets have carbs that are not rebuildable,once their gummed up their junk.
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Old 03-22-2011, 08:01 PM   #12
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I used the 15w-40 oil when I serviced my Onan last year. When I was at the NAPA store buying the air & oil filters, I mentioned to the guy I was surprised it called for a diesel rated oil. Counter guy told me it was probably for the higher detergent & additive levels-made sense....
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