Onan quiet diesel 8K 25 Year service

[Fredward]

We’ve got an 8k Quiet Diesel in our 2000 Country Coach. Works perfectly with about 3,000 hours on it. I am planning to remove it from the coach, remove the sides of the cabinet and completely go through it. Replace all the hoses, water pump belt, glow plugs, fuel pump, etc. It just seems like a good idea at this age to replace the simple things that could cause it to fail. Open to all opinions.

What kind of experience have you all had with the QD Series Onans that are 20+ years old?
Fred

[d23haynes57]

I would add checking or replacing the radiator and the rotor bearing.

[Fredward]

Thanks Dennis, good point - I never thought about the bearing. Radiator will be part of my project for sure. It looks good right now.

Where would you go for parts? I've purchased parts from cummins here locally in the past. Just wondering if there is a real good online place? Or someone who specializes in Onan QD gensets?
Fred

[Alpine36]

I had to pull our 2000 QD 7.5 last year to remove the inverter assembly for repairs.
While apart it received a new belt, thermostat, cooling system flush, new fuel pump and fuel filter and oil and filter change. It’s been a reliable unit until a diode failed internally in the inverter circuit board creating a no start condition. (no response from any switch and the fuel pump ran continually) I sent it to Flight Systems in Pennsylvania. About $1k for repairs and shipping. It runs like a champ now.

[Fredward]

Thanks Alpine. Yes an electronics failure like that is my biggest concern. It leaves you without power and out of luck until it can be repaired/replaced. There's no limping it along until you get back home! Fortunately I've not encountered that situation yet!
Fred

[d23haynes57]

The inverter sections are a weak link for this series generator. Note the 10K and 12.5K are constant speed generators so they do not have the inverters.
Probably the most common cause of failures is sudden surges, especially from the AC units. It is critical that the AC's get turned off by the thermostats when power sources are changed. Especially for the older coaches, the compressor start up time delays are from the thermostat, which is powered from the battery. The thermostat has no idea that power to the unit was disconnected. If the thermostat control is left on, then when the transfer switch connects all the AC compressors will try to start at once. This will be in addition to the battery charger, refrigerators, etc. Not good for the transfer switch or the genny.

[Alpine36]

Originally Posted by d23haynes57

The inverter sections are a weak link for this series generator. Note the 10K and 12.5K are constant speed generators so they do not have the inverters.
Probably the most common cause of failures is sudden surges, especially from the AC units. It is critical that the AC's get turned off by the thermostats when power sources are changed. Especially for the older coaches, the compressor start up time delays are from the thermostat, which is powered from the battery. The thermostat has no idea that power to the unit was disconnected. If the thermostat control is left on, then when the transfer switch connects all the AC compressors will try to start at once. This will be in addition to the battery charger, refrigerators, etc. Not good for the transfer switch or the genny.

Good advice, and what we’ve always done as well.
Sometimes stuff just fails no matter how cautious one is, but always wise to follow best practices. Bring those heavy loads back online one at a time.

[d23haynes57]

Originally Posted by Alpine36

Good advice, and what we’ve always done as well.
Sometimes stuff just fails no matter how cautious one is, but always wise to follow best practices. Bring those heavy loads back online one at a time.

I mentioned this as I know there are users that will leave the AC thermostats on and then start the generator while driving when they want the AC on.

[mokurt]

I would imagine a it will have a lot of dirt/dust build up.
Check the external radiator fins and fan blades for dirt.
Take a look at the internal radiator tubes for corrosion.

[sibe]

I have used these guys for some parts, in a pinch they may help..
https://www.partsfortechs.com/index....x&cPath=14_104

[d23haynes57]

These Onan Radiators are like larger heater cores for trucks and buses. Failure tens to be corrosion or erosion from the inside out and the end tanks leaking. If there is any sign of crud on it has been leaking. Using the better ELC engine coolants should reduce the internal wear from conventional coolants.

[Fredward]

Yes I wish I had a constant speed generator not one of these inverters. So I am very careful about starting and stopping when the Air Conditioners are involved. Always shut the AC off and let the Onan cool down for a few minutes. Always shut them off when switching from shore power to Generator power and then restart them one at a time. I keep thinking I should install a soft start kit on both units. I've seen the generator be unable to start one of the units for some reason; speed way up and then shut itself down! That can't be good.
Fred

[d23haynes57]

As a thought, 1,000 hours on equipment like a generator is roughly the equivalent of 40,000 miles on a car. That and 25 years of age that genny has served well. I had the 7.5K in my 04 Tropi-Cal and yes power needed to be managed but the variable speed quietness was real nice when used for overnight AC use. When only one AC was running and the Gen-Turi in use I didn't even know it was running.

[Fredward]

Agreed on the significance of hours. One of my biggest concerns/dislikes is that there are no gauges on mine. So I don't have any way to know relatively how hot its running or what the oil pressure is. This Kubota is a very durable engine as long as it is treated properly. I also don't like the inverter functionality. The 10k and 12k units run at a constant 1800 rpm. Which is basically what the Inverter runs at when its unloaded. And it spools up from there. I'd way rather have a constant speed unit. FWIW
Fred