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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

2010 Winnebago Tour model 40CD soon to be a 2016 Newmar Dutch Star 4369
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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:

2008 Itasca Meridian 37H & 2015 Flagstaff T12RBST
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27K miles & 41 states in 13 months - Woo Woo
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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
2010 Winnebago Tour model 40CD soon to be a 2016 Newmar Dutch Star 4369
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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
Toad - '08 Ford Taurus X
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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.
2010 Winnebago Tour model 40CD soon to be a 2016 Newmar Dutch Star 4369
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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??????

Old Scout
2003 40' MDTS
Garden Ridge, Texas
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