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Old 04-03-2013, 10:34 AM   #1
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Diesel generator coolant

I have the 12.5 KW Onan genny. It needs some coolant---but the manual is extremely vague ("use the best quality ethylene glycol coolant" with rust inhibitors and stabilizers). Does anyone know of somebody I can call at Onan or an onan customer support email address that will give me some knowledgeable advice. For example, can I use a high quality automotive product? What about using the same thing have in the ISM, Final Charge Global? What about some of the heavy duty diesel coolants that have SCA's? I know there are a lot of owners that have opinions---but sometimes that isn't based on knowledge. That's why I need someone to contact at Onan. Thanks
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Old 04-03-2013, 12:10 PM   #2
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Go to a local Auto Store and purchase a antifreeze that best matches Onan's description. Do not purchase a antifreeze that says it is compatible with all different types of antifreeze. If it does not say ethylene glycol coolant on container do not purchase it. I get mine at a Tractor Supply Company store.
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Old 04-03-2013, 12:13 PM   #3
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Our 8Kw gen has a Kubota 3 cyl engine. I use what is recommend for that engine although it's not as critical as the coolant for the Cummins ISC.
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Old 04-03-2013, 12:23 PM   #4
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Diesel genset motors are not wet-sleave so you dont need the anti-cav/DCA chemical brew required by Cummins diesels. Probably any brand name E-G based product will do [though I do get confused over green verses red, verses long-life, "compatible with all", verses bio-degradeable, etc, etc. I know quite a few folks use the same coolant in their gensets as they use in their Cummins to avoid carrying mulitple coolant jugs--cant imagine that the hi-priced DCA stuff wont work in the genset.
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Old 04-03-2013, 03:58 PM   #5
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Hi joelyn5,

The spec sheet for your generator is at

The operators manual is at

Both these documents, while informative, will not help you. The manual says just what you posted in the OP. If you are just adding coolant, I'd add coolant of the same color. If you are changing the coolant, consider putting the same coolant in the generator that you put in the engine. This way it is easier to remember what you have. That is what I did.

The contact number for Onan technical support is 800-888-6626.
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Old 04-04-2013, 08:23 AM   #6
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Generator coolant

Thanks to all for the information. The fellow that answered the 800-888-6626 at Onan was clueless. Didn't have any idea what I was talking about. Didn't know what a coolant with SCA was. All he could do was parrot what the manual said ("high quality ethylene glycol coolant"). Too bad they don't have better technical writers for the manual.
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diesel, generator

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