Onan 5500 generator: Surging + Overheat

goldenroads · 07-11-2016, 06:52 PM

Last weekend we heard our toy hauler's generator start to run funny -it was throttling up and down A LOT, with no changes in load. Looked it up, that's called surging apparently. I ran the generator for 60-90 minutes every month all winter while my unit was stored, I was told to do that to prevent varnishing, which is what I hear causes this.

Funny thing - when I went to look at the generator, it was CRAZY hot. I pulled off the cover and waved it back and forth, fanning the unit, and the surging slowed and eventually stopped -seems like it is overheating. I checked for obstructions as well as any leaks in exhaust -could not find anything.

Everything was fine last month, no issues at all. 4 weeks later, generator is acting crazy and it even shut down. Carbon monoxide sensor is even going off in the trailer now -this is really weird. Called the dealer, they will get us in to look at it -IN OCTOBER! We have a 3 week camping trip planned that we are not canceling, and it sure would be nice to have a generator for the trip...

Anyone heard of this? I can see the surging part being related to varnishing -who knows why that happened, but if it did, so be it -but the overheat? I couldn't even touch the manual start button, it was so hot -and that is rubber!

Toy hauler and all gear is only 13 months old. Generator only has 67 hours on it, not even close to a maintenance schedule, if I am reading everything right. I am stumped.

Grumpy · 07-11-2016, 07:21 PM

I'd call your local ONAN service center, they're good about answering questions.

abarkl · 07-11-2016, 07:28 PM

It's a bad fuel pump. Costs all of $30 to replace and takes 15 minutes. Here is the pump they use;
https://www.amazon.com/Airtex-E11015.../dp/B0076D5OI2

goldenroads · 07-11-2016, 07:32 PM

ok - I can't say I am surprised, based on what I have read online. I just am so confused as to how the fuel pump causes the overheating.

Is it something along the lines of it malfunctioning and running too rich, providing more fuel than can burn in the chamber and having it burn in the exhaust, or something like that?

I appreciate the help, I will see how I can get that replaced faster than Amazon (1-3 months) or my dealer (October)

Thanks!

Sundancer330 · 07-11-2016, 07:46 PM

It sounds more like the carb is gunked up with varnish, did you use an additive like Seafoam in the fuel over the winter. Even if you run it now and then it will still varnish up without some kind of additive. If you can't get it in for service add a heavy dose of Seafoam to the fuel run it some, let it sit then repeat a few more times, since its fairly new this may clean it out.

goldenroads · 07-11-2016, 07:53 PM

No - I just read that now in the service notes. Wish I had known! Will give that a try tomorrow! Have also heard good things about the 4C spray from Cummins

goldenroads · 07-11-2016, 08:04 PM

Is that the spray stuff? I just pull the air filter with the generator running and spray it in???

Sundancer330 · 07-11-2016, 08:08 PM

Quote:

Originally Posted by goldenroads

Is that the spray stuff? I just pull the air filter with the generator running and spray it in???

No Seafoam mixes with the gas, you want it to run through and clean the carb. All a spray will do is make it look pretty, it won't clean the internal parts of the carb that varnish up. You can buy it at any auto parts store.

Vaquero · 07-11-2016, 08:20 PM

Sounds like bad fuel.
I'd drain the tank and fill with fresh.

goldenroads · 07-11-2016, 08:29 PM

THAT would be an easy fix! any reasonable way to do that? It has about 20 gallons in there now. if that's all it is, great. just not sure how to do it, other than running the generator, which is the problem right now!

This is built into the front of our toy hauler, gas tank is towards the rear by the fuel station for the ATVs

shadester · 07-11-2016, 08:36 PM

I'm not really sold on the tarnish theory. Seem quite new for that in my opinion especially since your running it. If you can't wait, I'd pull the carb, then the fuel bowl and clean it out. Maybe you have sediment or something in it. Usually if your careful, once you loosen and remove the fuel cut off valve. Just lightly tap the bowl and it usually comes off without damaging the gasket. Sure, if your really run lean the engine will run hotter than usual. Are you sure you didn't get some bad fuel or something???

goldenroads · 07-11-2016, 08:38 PM

anything is possible. do you know of a reasonable way to empty and reload? there is about 20 gallons in the generator fuel tank now. other than running the generator, which is the problem, I don't know how to get it out!

Vaquero · 07-11-2016, 08:38 PM

Quote:

Originally Posted by goldenroads

THAT would be an easy fix! any reasonable way to do that? It has about 20 gallons in there now. if that's all it is, great. just not sure how to do it, other than running the generator, which is the problem right now!

This is built into the front of our toy hauler, gas tank is towards the rear by the fuel station for the ATVs

I pump my old welder and generator gas into the farm truck and refill with fresh twice a year.
I'm not familiar with your setup, but old gas does cause the surging you mentioned.

Seafoam may help.
Dad always put a cap full of rubbing alcohol in the grain truck gas tanks. (Seasonal use for sure) to displace water from condensation.

shadester · 07-11-2016, 08:40 PM

Quote:

Originally Posted by goldenroads

anything is possible. do you know of a reasonable way to empty and reload? there is about 20 gallons in the generator fuel tank now. other than running the generator, which is the problem, I don't know how to get it out!

I'd rig up a external tank of fuel prior electric fuel pump and try it first. hook a line into the inlet side of electric pump.

Vaquero · 07-11-2016, 08:45 PM

All this new 10% ethanol fuel,is not air cooled engine friendly.
The longer it sets , the worse it gets.
Just too much water to begin with.

Sundancer330 · 07-11-2016, 09:01 PM

Quote:

Originally Posted by goldenroads

THAT would be an easy fix! any reasonable way to do that? It has about 20 gallons in there now. if that's all it is, great. just not sure how to do it, other than running the generator, which is the problem right now!

This is built into the front of our toy hauler, gas tank is towards the rear by the fuel station for the ATVs

With Seafoam just add it to your fuel tank, the mix is 1oz per gallon. Since you have about 20 gallons I would buy two 16oz cans and $8 each and add both for a heavy dose, directions say max is a 50/50 mixture. Then run the engine to get the mix in the carb and let it soak internally do this a few times. Go check out there web site, its amazing what this stuff can do.

abarkl · 07-11-2016, 09:03 PM

If it continues to surge after replacing the fuel pump then the carburetor will need to replaced.
It's more expensive but only takes another 15 minutes to replace;
https://www.amazon.com/Cummins-54107.../dp/B00B35JVEC

The 5500 I owned for 10 years did get hot when running and when the ambient temperatures were above 75F the fuel pump would get too hot and cause the genset to either surge or not run at all.
The last few years I have owned Onan QD Quiet Diesel gensets which don't suffer from the common failed fuel pump issue or have a carburetor to become gummed/varnished with gasoline. And although I don't usually have a reason to check or choose to touch it while running I'm sure it's quite hot under load.

goldenroads · 07-12-2016, 07:22 PM

So I drained the gas, refueled with Shell Gold gas and it now seems to be running fine. I hit it with the A/C and the electric water heater for loading, figured that was a pretty decent test.

20 min, only one hiccup - a slight sputter.... Enough to kick the AC power off, so will continue to require monitoring but it sounds a LOT better so far.

Progress? Hope so.

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