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Old 04-21-2016, 06:22 PM   #1
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Onan Generator service

Hello, I own a 40' Winnebago Tour with an Onan 8HDKAK-1046L RV QD8000 generator. I've looked and looked, called Cummins and still I can't a direct answer. Here's my issue. I want to drain the coolant and refill with a fresh supply. There's a drain on the bottom of the generator and just a little over a gallon emptied from the generator. (Cummins says it holds 1.2 gal's) My local Cummins dealer in Fontana, Calif. said I needed to remove a small side panel from the passenger side of the generator to fill the radiator, Cummins 24/7 says to fill it through the radiator cap.

I don't have a small side panel (on the left or right side of the generator) so I decided to fill it via the radiator cap into the plastic coolant tank. I poured coolant into a funnel and into the tank and it started spilling out into the container I had under the generator. I let it sit for a while and the level hasn't gone down. The coolant is now above the "HOT" mark on the tank. Like I said, Cummins was no help, both the 24/7 hot line and my local dealer. I'm hoping one of you kind members has some information that will be helpful.

thanks in advance

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Old 04-21-2016, 08:25 PM   #2
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If your 8kw generator is similar to the 7.5kw generator you have to pull the radiator fill cap & hose assembly completely out of the opening to allow the coolant to freely flow into the system. There is a small panel near the start button that you have to take off and pull the filler cap out.

I had a similar issue with my 7.5 onan and thought OK, it's air locked and if I start it the system will burp and the fluid will flow.

IT DIDN'T, I blew the engine and had to replace the generator with a used on for $5K. Not an enjoyable experience.

When I finally took the whole enclosure apart I found the problem, the hose filler and coolant cap were kinked and in a bind. I did try to pull it out when I was trying to fill and thought I would break something if I pulled any harder.

Lesson learned, hope my post helps you avoid making a mistake like I did.

Hope this helped.

Jim J
2002 Monaco Windsor 38 PKD
2005 Jeep Grand Cherokee w/5.7 Hemi
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Old 04-21-2016, 08:31 PM   #3
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Good video here:

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Old 04-22-2016, 06:31 AM   #4
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The information provided by jacwjames and bluepill is what makes this site so valuable. I really appreciate the help.

Thank you very much !!!!! You just made my day (doesn't take much to make me happy) LOL
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Old 04-22-2016, 08:46 PM   #5
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That entire series of videos is excellent, it covers all the routine servicing items extremely well. Thanks to everyone who helped make them available.
'07 Winnebago Journey 34H, ISB-02, MH2500
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Old 04-22-2016, 10:34 PM   #6
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Today, I started and finished the coolant drain and refill, In reality it takes more steps than when I drained my Cummins engine and refilled with new coolant (1 gallon in the generator vs 11 in my ISL) but it was actually easier than the generator.

A little disappointed in Onan or Cummins for a poorly designed generator. Not everyone has a slide out generator to service the thermostat, hoses and belt and, who ever came up with the idea to "hide" the radiator fill nozzle behind a bolted on plate wasn't thinking or was on bad drugs.
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Old 04-22-2016, 10:45 PM   #7
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I agree...$1600 to change thermostat and belt. Had to have the entire unit dropped from coach and of course mounting bolt design was also a problem(seized and had to be drilled out).
Could have been worse obviously, but still a very poor design.
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Old 04-22-2016, 10:52 PM   #8
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Fortunately, my Onan 7.5 is on a slide but access to some of the panel bolts on the bottom edge of the genset is a buggar. Need to check the water pump belt for wear/tear every couple of years--recommend you carry a spare. While you have the top panel off to check the belt, wash off the radiator and engine components--dont get the generator/ electrical brain boxes wet. If your dash A/C condensor is located above the genset and drips condensation on the top of the genset from time to time--recommend using putty/butyle tape to seal the forward panel seams on the genset.
Bonus question--who knows where the spark arrestor is located and how/how often to service it??????

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2003 40' MDTS
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