Community Forums

RonNBama · 06-17-2011, 08:25 PM

My 7500 Quiet diesel Onan konked out during a trip this past week. First code it showed was "low speed shutdown #26. I managed to get it running again for a few hours and it finally quit completely and is showing a #36 (air filter, fuel filter, air in line) code. Changed all filters (oil, air, fuel) but she still will not start. Anyone peered under the cover of one of these? I hope to expose the beast and clean the injectors this weekend and am searching for any particular "gotcha's" to avoid.

Is there a "reset" for the trouble codes?

texnet · 06-17-2011, 08:36 PM

Do you have at least 1/4 of a tank of fuel? I know mine quits when I allow the fuel tank to get below 1/2 tank.

RJay · 06-17-2011, 08:36 PM

You might have some air in the lines. Try holding the start/stop switch down in its Stop position for at least 1 minute.

RonNBama · 06-17-2011, 08:45 PM

Yep, first time she shut down was immediately after topping off the tank (with the gen set running). Thought I might have stirred up some crud that made it through the filter. Actually ran for about 2-hours the next day before finally stopping completely. Did a fuel filter replacement and held down the prime button for a minute (did this a couple of times).

I suspect air in the line. I loosened the output side of the fuel filter connection and pumped some diesel out and ran through the prime/purge sequence a couple more times.

Forgot to add that it is almost at the 1000 hour mark so a service may be in order anyway. Just hate to turn it over to a shop for days (or weeks) if there is any way to trouble-shoot it myself. Think $$$$$ and a fixed income and you'll understand.

RJay · 06-17-2011, 08:50 PM

I hear ya Ron, do as much as you can. Based on what you've done so far there shouldn't be much more that's needed.

Mike Canter · 06-18-2011, 01:55 PM

Ron, I just completed the 1000 hour check on mine myself. Pretty hard to do. I changed the fan belt, hoses, coolant, oil and filters and adjusted the valves. All the valves were at .012" vice .008". The belt is hard to get to and I would not want to do it on the road. If it was me I would get your geneerator running normal first otherwise it could get complicated if you had a problem doing the 1000 hr check. I would not mess with those injectors. I doubt that you got dirt past the fuel filter that only happens in fairy tales and on forums. Are you reading any codes for it when it will not start?

Gary RVRoamer · 06-18-2011, 02:29 PM

I've got 1800 hours on mine with only filters and fluids changed (regularly). I think Onan's maintenance schedule is ultra conservative.

The code 22 is basically an overload of the generator without tripping the breaker. The governor is unable to get the engine to run fast enough to handle the current load, even though that load is less than the max rated (63 amps). Most likely an engine operation problem and could be fuel filter, fuel pump, air filter, etc.

Code 36 is a catch all - the engine quit and they don't know why. Low fuel in the tank is one easy one, but again it could be fuel or air starvation.

I haven't heard of injector problems in that little diesel, but I guess its possible.

RonNBama · 06-19-2011, 06:45 AM

Thanks guys. I did not realize that the 1K hour tune-up had so much stuff involved. I do plan to try to get it running and see how things go from there.

Oh, first code was 26 (underspeed). Second (current) code is 36 (catch all I guess).

I'll refresh this thread when and if I find the problem....

Mike Canter · 06-19-2011, 07:29 AM

Let me tell you exactly all I found. The radiator hoses were not swollen but just starting to and had several real bad rub spots because they were rubbing against bolts or other sharp objects. The one radiator hoses runs under the exhaust manifold and there is a metal clamp to hold it and adjust the position. It had moved either from vibration or not being positioned correctly to start with. The other hoses just had several rub spots. There were no cracks on the fan belt but it was not very flexible. The problem is with the belt if it ever breaks it will be a nightmare on the road to change. The valves were evenly out of adjustment. The excess gap would just cause a little noise and less power and a litlle more fuel consumption.

To get at all this you have to loosen the front panel, then take off the top panel and the back and drivers side panel. Curb side stays on because there is a little access panel down on the lower right side that opens up and lets you get at the hose clamps where the hoses attach to the radiator. To get the fan belt off you now have to remove the rear fan housing, then the fan, the the rear bulkhead. Now you can get the fan belt off. I also replaced the thermostat, the radiator cap and the coolant.

One thing I did find is opening that coolant drain plug does remove all the coolant from the system. I also opened the drain plug on the side of the engine block but nothing more came out.

Total parts was around $170 because those hoses are very complicated and not cheap. One of the problems is the parts book called for the posssiblity of two size thermostats. We picked the smaller one and yep it was the bigger one.

Gary RVRoamer · 06-19-2011, 08:00 AM

Mike... is that the10k Onan you are describing? I don't recall a curbside access panel on my 7.5k Onan QD. There is one underneath on the front curbside, though (air filter access).

Mike Canter · 06-19-2011, 08:09 AM

Yes, you are correct, that is a 10K & 12.5K I am describing. So that means you will have to take off another 100 10mm bolts. You only need like three sizes of wrenches/sockets, the most commeon is 10mm. then a 12mm and a 13mm.

RonNBama · 06-20-2011, 05:37 AM

Uhhhh, I think I will just drop my coach off at Mike's garage.

Know what you mean about the multitude of 10mm bolts. Just got started and already have a bucket full of them! Have not removed the rear panel yet but can see/reach the fan belt and it is very loose. One thing I noticed is that the coolant filler hose is pinched badly. Don't see how water could possibly be added to the system through the radiator cap. Looks like the hose is about 6" too long or maybe routed improperly.

Mike Canter · 06-20-2011, 05:47 AM

Ron, believe it or not that pinched coolant hose is the way it is designed and is talked about in the Onan Service Manual. It seems to work just fine how it is.

Dr4Film · 06-20-2011, 06:23 AM

Speaking of pinched hoses, I had my generator running to power the front A/C on a trip south from Alaska last year. We were in WA state heading for OR and the generator had been running for 200 miles or more. As we pulled into a rest stop off of the I-5, the generator just quit. Attempted to restart but it acted like it was starving for fuel. Since we had an appointment the next day in Coburg at the Cummins shop for something else I had them check it out. They found a pinched fuel line hose that for whatever reason decided not to allow enough fuel to reach the generator anymore. It was pinched with a zip-tie where the fuel line makes a turn at the corner of the box. When the generator was slid out it would work fine, when it was slid in, the flex in the line and cables caused the fuel line to restrict. Go figure.

And to think that it ran for well over 200 miles or more previously with no problems.

Dr4Film ----- Richard.