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Old 04-20-2018, 10:33 AM   #1
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Onan QD8000 overheat issue that may not be overheating

I recently purchased a Haulmark sport deck toter from a friend who got it at a salvage auction. They fixed the truck up and I ended up with a nice rig for a reasonable price. Since it's an auction truck that was wrecked, I don't have any history on the truck, and I am working through problems as they come up. A big one is the QD8000 (HDKAK) generator. I've had to work through all sorts of issues with the unit. New fuel pump, push fuel pump at diesel tank, new fuel line, new 12v leads to batteries. But there has been a pressing overheating issue that I cannot solve.

If the truck is parked, the generator will run without fail for hours with the AC on high. If you take it down the road with the AC on after a short period of time the generator will shut off and give code 33. Last night I drove the truck and it shut off right as I pulled up to the house, I hopped out and restarted it, and it ran fine for hours again, so I am not sure that it's actually getting hot.

So far I have replaced the temp sender, thermostat, cap, flushed with Fleetguard flush 4x. Due to the setup of the truck getting the radiator out isn't an easy prospect without pulling the entire genset, which isn't on a slide and has little clearance for a lift.

The baffling part to me is that it doesn't actually seem like it's getting hot. My guess is loose or shorted wiring that a bump makes short out, however I would think I'd get a different code and not the overheat Code 33. What is also strange is that it won't do it if the AC isn't running.

I'm baffled, has anyone experienced something similar?
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Old 04-20-2018, 01:58 PM   #2
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Hi ! Welcome to IRV2! We're sure glad you joined the gang!

Can't help with the genny but wanted to say hello!

Good luck, happy trails, and God bless!
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Old 04-21-2018, 11:26 AM   #3
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Is the generator on the driver side or passenger side?

When looking at the generator, the exhaust is out the bottom right and the cool air intake is in the bottom left. If mounted on the driver side, this is not an issue. If mounted on the passenger side and the vehicle is moving, there can be hot air recirculation into the cool intake air.

There could also be an issue with a loose wire as you said. What happens when driving with the generator running under no load? If it still faults out with lite load, I would think a wiring or sensor issue. If it only faults when driving and under load, I would think hot air recirculation.
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Old 04-23-2018, 07:23 AM   #4
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Is the generator on the driver side or passenger side?

When looking at the generator, the exhaust is out the bottom right and the cool air intake is in the bottom left. If mounted on the driver side, this is not an issue. If mounted on the passenger side and the vehicle is moving, there can be hot air recirculation into the cool intake air.

There could also be an issue with a loose wire as you said. What happens when driving with the generator running under no load? If it still faults out with lite load, I would think a wiring or sensor issue. If it only faults when driving and under load, I would think hot air recirculation.
The generator is on the driver side at the rear of the coach, right in front of where the truck exhaust comes out, so the cool air intake is in front.

If the generator is running under no load when it's not hot outside it will stay running, I haven't let it run with no load when it's hot because I like AC, so I will need to check that.

What's strange is that if it "overtemps" I can restart it immediately (I restarted it within a minute of it dying and me stopping) and it will stay running, I would think if it were actually hot it wouldn't restart that quick.
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Old 04-24-2018, 06:43 AM   #5
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You say the vehicle exhaust is behind the generator, so that shouldn't be an issue. Is there any other way vehicle engine heat could make its way to the generator? where is the radiator for the vehicle engine?

Have you done a pressure test on the cooling system? You said you've replaced the cap recently, but does the system pull coolant in from the overflow tank? Perhaps there's an air bubble that gets to the water pump only when you're driving and shaking the system around.

Is the belt to the water pump tight and in good condition? Looks like the HDKAK doesn't have a battery charging alternator, so there is no way to re-tension the belt.
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Old 04-24-2018, 07:58 AM   #6
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You say the vehicle exhaust is behind the generator, so that shouldn't be an issue. Is there any other way vehicle engine heat could make its way to the generator? where is the radiator for the vehicle engine?

Have you done a pressure test on the cooling system? You said you've replaced the cap recently, but does the system pull coolant in from the overflow tank? Perhaps there's an air bubble that gets to the water pump only when you're driving and shaking the system around.

Is the belt to the water pump tight and in good condition? Looks like the HDKAK doesn't have a battery charging alternator, so there is no way to re-tension the belt.
It's a Haulmark Sport deck, the generator is 30' behind the engine, so it's definitely not getting engine heat.

I haven't pressure tested the cooling system, and I'm not sure if it pulls coolant from the overflow. I will work on that. With the cap off and the genny running the lower of the two smaller hoses right behind the cap is returning coolant under pressure.

The water pump belt is tight.
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Old 04-29-2018, 05:00 PM   #7
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I had the same unit in an 04 Country Coach with same symptoms & code. I dropped it and sent it to a generator facility in Dallas. Got it back in same shape. Dropped it again and they ran it for days. Bottom line-new radiator cap and never had another issue. Didn’t pay for the second drop either. Good luck.
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Old 04-30-2018, 08:20 PM   #8
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I had a similar problem with a smaller onan, it would work great with the AC running while sitting still. But when I was rolling with the AC on the generator would trip the breaker or just quit running. I don’t remember the error code but I could crank it right away and parked it ran great but rolling it would trip breaker or just quit. It was still under warranty so the dealer had to solve the problem. They drilled some 1” holes in my AC shroud cover to allow the AC better air flow. The generator worked perfect after that until I traded it for a different RV.
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Old 05-08-2018, 03:43 PM   #9
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Swapping the cap today, I thought I did it when I did the rest of the service, but I didn't do the cap, only the tep sensor, flush, and thermostat. I'll report back.
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Old 05-08-2018, 04:40 PM   #10
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Welcome.

Did you follow the Onan procedure for burping the coolant system? Just a thought.

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Old 05-08-2018, 09:42 PM   #11
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We recently had our mobile mechanic come out to the house and do the 1000 hour service. Big job, had to pull all the panels off to replace the 4 coolant hoses. Here's what he did to refill the coolant. First, he pulled a vacuum on the coolant system and did a 5 minute test checking for leaks. Then he used that vacuum to draw coolant into the system, effectively eliminating any air being introduced into the system. Worked like a charm.

The 2 times that I have flushed and filled the system the old fashioned way I had a heck of a time getting the air out. The genny would shut down and throw the old 33 code. I'm betting this is your issue and the genny running while parked and shutting down while going down the road are coincidence. These Onans are very protective of themselves but are virtually bulletproof when properly cared for and maintained. Ours has nearly 3000 hours on it.

My only other thought is that this setup has been backyard engineered and has never properly worked while underway. Maybe while running down the road some strange air turbulence is occurring that is preventing the unit from properly cooling. Unlikely but pointing a heat sensing device on the coolant cap might give you some clues. Either way, that is one expensive genny and worth trying to get working right. Good luck.
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Old 05-09-2018, 01:36 PM   #12
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We had an overheat issue with ours (new purchase, used coach) and it ended up being a plugged radiator. It would run fine until a large load was put on and then it would shut down due to overheat. They found it by checking the temps across the rad core, almost no temp drop was seen. It was found during the 1000 hr service, they do a load check as part of the service.
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Old 05-09-2018, 09:51 PM   #13
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We had an overheat issue with ours (new purchase, used coach) and it ended up being a plugged radiator. It would run fine until a large load was put on and then it would shut down due to overheat. They found it by checking the temps across the rad core, almost no temp drop was seen. It was found during the 1000 hr service, they do a load check as part of the service.
This is the conclusion I have pretty much come to.

When I try to burp the system I run into troubles because coolant sprays under pressure out of the radiator vent tube (the lower of the two small tubes). I'm not sure if this is normal either.

What really stinks is that the generator is not on a slide, and there is no room to work to get the radiator out.
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Old 06-11-2018, 01:29 PM   #14
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Wanted to post an update to my QD8000 overheating issues and now a new problem.

So I stupidly overlooked that the panel below the fuel filter was missing and has been missing since I've owned the toter, so minimal air was getting over the radiator and it was all dumping out the bottom of the unit. This is why it would run parked but not driving, the force of air while driving created a suction that caused all of the air to go out the bottom. I built a panel and the problem seemed solved. We ran the genny for 24 hours straight while driving and camping in fairly hot conditions with the AC on, zero issues, no shut downs. A week later we drove home from our trip with the same results.


THEN... the next time I ran the camper it started overheating again, it is hotter, and the AC was running harder, but still the conditions we not much different. I did a residential conversion and was able to leave the AC off and the genny would stay on. I burped the system for the 1000th time, and it looked plenty full.

On our way home I tried to run the genny again for the fridge and now it wont start. When you push the start button, it primes, then blinks code 33, it won't even crank, even after sitting for days it does this. I am currently at a loss, it's like the sensor went bad, but I think that has it's own code.

This entire deal has been so frustrating, and unfortunately there is no easy way to pull the genny to work on it properly.
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