Onan 2800 generator overheating

Darel · 10-26-2022, 12:02 AM

So my 2800 runs well and charges, but depending on load and outside temps it will shut down after running anywhere from 20 mins to an hour later.

For instance running the fridge, AC and temps around 70 and VERY humid it didn't last 20 minutes today. Sometimes if I'm just charging the battery and it's in the 30s outside it'll run for over an hour.

I did just service the unit (oil change, new spark plug, new filters, adjust altitude compensator) and no improvement.

I added in one quart of oil which it just over the mark on the dipstick. I then saw some evidence that overfilled onan units will shut down like mine. Does oil quantity have anything to do with overheating?

Where else can I start looking?

Thanks,
Darel

mkguitar · 10-26-2022, 12:27 AM

what indicates overheating ?

I'm in Arizona where the genny is often run at temps well over 100º

Darel · 10-26-2022, 12:29 AM

Everything I describe above.

I need my generator to run like yours.

booster · 10-26-2022, 01:03 AM

Quote:

Originally Posted by Darel

So my 2800 runs well and charges, but depending on load and outside temps it will shut down after running anywhere from 20 mins to an hour later.

For instance running the fridge, AC and temps around 70 and VERY humid it didn't last 20 minutes today. Sometimes if I'm just charging the battery and it's in the 30s outside it'll run for over an hour.

I did just service the unit (oil change, new spark plug, new filters, adjust altitude compensator) and no improvement.

I added in one quart of oil which it just over the mark on the dipstick. I then saw some evidence that overfilled onan units will shut down like mine. Does oil quantity have anything to do with overheating?

Where else can I start looking?

Thanks,
Darel

Watch the AC as it is running to see if the compressor starting is causing the issue as it cycles. If so, you might want to put and easy start on the AC.

The AC by itself is close to the capacity of the Onan when it starts, and if you have an absorption frig on AC and are charging batteries that are low, it would not be surprising that you are killing the Onan.

It may also have slight or moderate jet plugging in the carb from the gas, so running some Seafoam through it would not hurt.

Darel · 10-26-2022, 01:08 AM

Thanks. I should say I've only ever tried to run the AC once or twice because of this. When it kicks on the generator really bogs down.

I have a 12/120 compressor fridge just fyi.

I'll give the seafoam a shot but I'm not holding my breath.

booster · 10-26-2022, 01:37 AM

Will it restart right away or do you need to wait? If so how long a wait.

A weak fuel pump will vapor lock sometimes when it gets hot.

The coil and ignition module could do similar.

Bad grounds that heat up also can do it.

Darel · 10-26-2022, 09:44 AM

Has to wait. Usually an hour or more. It's pretty clear it needs to cool down before it will restart.

Thing is, I would think none of those things would be dependent on the load. The fuel pump doesn't have any more of a load on it with the AC on than it does just idling away. Same with ignition components? Or no?

I mean, it has almost 1800 hours on it, I probably should replace all those anyway. Thing is it's in such a terrible spot slung under the rear of the van, just servicing it was a 4-hour nightmare. I feel like if I'm going to get into any of that it's going to mean completely removing the generator to work on it. So I'm kind of in denial about all that.

Thanks!

booster · 10-26-2022, 10:48 AM

Quote:

Originally Posted by Darel

Has to wait. Usually an hour or more. It's pretty clear it needs to cool down before it will restart.

Thing is, I would think none of those things would be dependent on the load. The fuel pump doesn't have any more of a load on it with the AC on than it does just idling away. Same with ignition components? Or no?

I mean, it has almost 1800 hours on it, I probably should replace all those anyway. Thing is it's in such a terrible spot slung under the rear of the van, just servicing it was a 4-hour nightmare. I feel like if I'm going to get into any of that it's going to mean completely removing the generator to work on it. So I'm kind of in denial about all that.

Thanks!

All of the heat affected parts are load dependent because the temp inside the case increases with load due to the engine and generator heat generation as they work harder. This is especially true for cased air cooled engines which can get very hot under heavy loads. IIRC, Onan does suggest a period of no load running to cool things down after a high load run of the generator.

Darel · 10-26-2022, 10:51 AM

Makes sense. Thanks!

SteveJ · 10-26-2022, 11:06 PM

Get the oil level correct. You say you added a quart. IIRC, the total capacity is one quart. Something is wrong here. You were either running with no oil(!) or you are over full now.

I had the same issue with our problematic 2800. It turned out to be the voltage regulator, taken out by high resistance in the slip rings.

Time to drop the genny.

Darel · 10-26-2022, 11:45 PM

I CHANGED the oil. Removed existing and refilled with one quart, which is spec. This put me a hair over full on the dipstick. I plan on draining a little bit out to see if it helps.

Deano · 10-27-2022, 10:48 PM

My vote is to replace the fuel pump and mount it outside of the genny. Makes a possible future replacement easier.
Search for previous posts about this.

JohnnyFry · 10-30-2022, 07:30 PM

I would suspect the fuel pump. A common indicator of impending failure is shut off when the genny gets hot. Some have moved the pump outside the generator enclosure when replacing. This keeps it away from the heat and makes subsequent replacement east. If the generator won’t immediately restart but is ok after an hour or so, suspect the pump.

blackbourn3704 · 10-30-2022, 10:34 PM

A simple way to check the fuel pump is to disconnect the fuel line from the carburetor and plug the line. Set up a gravity siphon from a jerry can positioned higher than the gen set. About 1 gallon should run the genset for almost 2 hours. If it keeps running that is a good indicator the pump was bad. For further proof instead of plugging the line from the pump to the carb, hookup a hose and catch the pump's output in a separate container while the generator is running from the gravity feed. The pump SHOULD deliver more than gen used in the same time period. (Don't smoke while doing this!).

Darel · 11-01-2022, 10:25 AM

Ok. So I believe the fuel pump just died completely. Trying to order a new one, but for some reason I cannot find anything listing parts for a 2800 Microlite KV-F. Lots of other respects, but not an F. Can't find a parts manual that covers it. Again due to the location of this damn thing I really need to have parts on hand ready to go, otherwise it's drop the generator, figure out which fuel pump I need, then order it, wait a week or more without a generator, then stick the thing back up in here. I need to be able to drop it, swap parts and put it right back in. Can't afford to have the van down for that long. Any thoughts on KV-F parts? Or specifically a fuel pump?

booster · 11-01-2022, 11:56 AM

Quote:

Originally Posted by Darel

Ok. So I believe the fuel pump just died completely. Trying to order a new one, but for some reason I cannot find anything listing parts for a 2800 Microlite KV-F. Lots of other respects, but not an F. Can't find a parts manual that covers it. Again due to the location of this damn thing I really need to have parts on hand ready to go, otherwise it's drop the generator, figure out which fuel pump I need, then order it, wait a week or more without a generator, then stick the thing back up in here. I need to be able to drop it, swap parts and put it right back in. Can't afford to have the van down for that long. Any thoughts on KV-F parts? Or specifically a fuel pump?

I can't help on the part number, and Onan has quit supporting the non inverter generators so they may also not be much help. Probably best to call one of the small engine suppliers of Onan parts. You should be able to find them by a search on the internet. They probably know what fits the various revisions.

Not really a big deal to use the van with generator out. Just plug the fuel line, cap off the wires that are left, and tie them all up to keep them from bouncing or dragging. Only a couple of minutes work, normally. The only real wasted time will by in relifting the van when the genny is ready to go back in.

Darel · 11-01-2022, 12:27 PM

Except that 5 days a week I have to live in the van, and I need to drive it 3 hours to get to my real home where I can do this work....which means doing that twice if I don't have parts on hand.

It looks like the fuel pumps basically come in two flavors, one with two threaded connections and another with one threaded connection and one hose barb. I can't even find a place that lists any pump for a 2800, the only ones I see called out by model are for 4000 and 5500s. Can anyone give me an idea if I need the double threaded one or the hose nipple one?

Darel · 11-01-2022, 12:37 PM

DISREGARD! I figured it out. I have been looking at my model number all wrong. What I thought was a "2.8 KV-FN26100G" was actually a "2.8 KV-FA/26100G". Figured out that I need a 149-2615 pump. Thanks guys!

Paga · 11-01-2022, 06:59 PM

I'm sure you are planning to replace the fuel and air filters, and spark plug while your Microlite 2800 genset is out, if you haven't been able to in place. I offer one more suggestion, but I realize your downtime is severely limited. Perhaps this will help others with Onan gensets however:

Generator Brushes and Slip Rings
It would be wise to inspect and probably replace the generator brushes, and clean/smooth up the slip ring surfaces with a slip ring polishing stone as needed, while it is out on the service bench. If they haven't been serviced in 1800 hours just be aware that if a brush loses contact with it's slip ring, the generator will not output. Often that also means the engine will start just fine, then may immediately die, as there is no 120 VAC output to the controller.

Unfortunately, physically getting to the brushes and slip rings is not a simple task. The Service Manual covers the procedure well, and there are some You Tubes that can help. I did this service on a failed 2013 Microlite 4000 this summer; the engine would start up and run, but then die immediately.

Going through the troubleshooting pinpointed the loss of connection (completely open) between the controller to the rotor, via wiring, brushes or an open rotor. On your 2800 the rotor winding resistance should be close to 16 Ohms per the Onan Service Manual. That can be measured from the controller connector. See the troubleshooting reference below, I found it to be extremely helpful.

One doesn't really know what failed until it is opened up. Mine had a completely worn out brush that had arc damaged that slip ring. I cleaned that up with the slip ring polishing stone. I was pleased to find that the rotor windings were fine.

Another source for troubleshooting information I used is Flight Systems. The slip ring polishing stone is available at Advanced Service and Parts.

I hope this all helps someone someday.....

Darel · 11-01-2022, 08:46 PM

I already did a general service a few weeks ago. I don't really see an open window to do the other work you recommend.

Honestly at only 2800w this thing isn't worth me putting any serious time or money into it. I can get one with twice the output for under $1000 and just haul it around on a hitch rack. I'll throw a hundred bucks at it or so but I do it knowing it's a losing battle on a 25 year old undersized and worn out unit.

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