Airstream Forums

Airstream Forums (
-   Mechanics Corner - Engines, Transmission & More... (
-   -   Onan Generator (

87MH 12-06-2003 06:35 PM

Onan Generator
Those of you with Onan Generators may find this interesting.

As some of you know, my 6.5KW with 750 hours on it has been giving me trouble lately. A quick rundown of symptoms and solutions:

July - Generator surging and eventually died. I was on the road traversing New Mexico and Texas at the time, on the road, so I was unable to troubleshoot right away. I suspect that the surging led to the demise of the front AC later in the summer. I did not have a 110 volt meter monitoring the voltage in the coach at the time. I cannot emphasize more the importance of this $25 tool. It’s impossible to tell by the sound of the genset alone when an overvoltage is occurring. I bought a “carburetor rebuild” kit for about $80. It just had gaskets, jets, and seats. I installed carb kit and new points and plugs, changed the oil and filter, the genset ran for a couple of months (maybe 8 hours), but I could not find a “sweet spot” for either of the jets.

September – genset starting to surge again (this time with a voltage meter in the coach – voltage ranging from 80 to 140+), not wanting to ruin the new AC, finished the trip with no cabin AC. AB informed me that if I ever wanted her to travel with me again, to get that d#*@ thing fixed. Being the dutiful partner that I am, purchased a new Nikke carb for $140. (Should have done that from the start – note to all others – don’t rebuild, buy new.) After installation, genset ran for about an hour, but was spitting a huge amount of carbon out the exhaust, and would not carry a load. Both new plugs were heavily carboned (but both plugs were sparking), and fresh oil change heavily contaminated with soot. Pulled the street side head, lots of carbon, but all appeared to be OK. I suspected a sticking valve on the curb side cylinder. PeterH suggested a compression check, found 125 cold/130 hot on both cylinders, not great, but it should run.

December - After it got to the point that it would not run at all except with the starter engaged, found that the plugs would not spark without the “starter” switch engaged.

Remembered one of the other 345 owners here also had a surging problem, and a shop replaced the R1 resistor, solving his problem. Measured the resistance in my R1 – right on at 100 ohms. As a last ditch effort, I decided to replace all of the electricals in the starter switch box. $100 worth of resistor, relays, diode, switch and solenoid and 8 hours later, it’s running like a new unit. Even had to back in the throttle linkage in about a half-inch to get the voltage down to 125 volts (paint still on the linkage threads at this setting, this may be the best it has ever run).

Don’t know for sure just what the problem was (again, the R1 resistor tested good after replacement), but wanted to pass on the forum what I found. Bottom line – on a 20 year old genset with 750 hours, recommend, as preventive maintenance, install new points, plugs, carb, and all start/run electricals.

Total parts - $300
Piece of mind - Priceless

swebster 12-06-2003 07:06 PM

Where did you get your parts?
Thanks for the rundown. Mine is back to quitting when releasing the start button. I've replaced the R1 (which did work for a while) but have it down to the start/run relay and the oil pressure switch.

Where did you get all of the parts (and what were they?)

I'm traveling without the genset running which is usually no problem but want to resolve this soon. Its cold out there and the coach batteries don't always make it through the night. would be nice to run the coffee maker once in a while.

87MH 12-06-2003 07:19 PM

Purchased the points, plugs, carb kit, and the carb from PPL here in Houston.

Southern Plains Cummins is the Onan distributor for Texas, got all the electricals from them, but the relays are OEM Bosch (used on Fords for sure, replaced several of them on my '92 one ton diesel and '96 high-top van). Switch, diode, solenoid, and R1 resistor also appear to be generic.

I'm not real close to any good parts shops here, so instead of running around for the cheapest parts, I got them all at So. Plains Cummins. BTW, the Bosch solenoids (in Onan boxes) were not an exact fit, had to clip 1/4" from the end of the mounting tab to make them fit "in the box". An aggravation, to be sure, but faced with the choice on cutting the tabs off, or fighting traffic all the way across Houston twice (there and back), it was a no brainer.

I have a service manual and parts book on order. Let me know if you need a schematic.

wb13798 12-06-2003 09:04 PM

i had the same problem with my onan 6.5 and the problem was the regulator module. cost $150 with a discount. the onan repair man in huntsville did it for me and i havent had a problem . i did replace the carb with a ebay take off it cost $39. a service shop in oregon had converted new gas to propane for customers and sold the carbs and fuel pumps on ebay . think i got the pump for $25 not sure. both were a steal. onan loves those that comes in the door with deep pockets.

87MH 12-06-2003 09:13 PM

Regulator Module

I wonder if yours may be a bit different than mine. I don't think I have a regulator module, unless it is buried way down deep inside.

In the "run/start/stop" section of mine are a resistor, a diode, two 1" cube standard control relays, the starter solenoid, and the start/stop switch. The oil pressure kill and the points and coil are external to the control box.

Just wondering if I should be looking for other balck boxes.

I do not have a service or parts manual for it as of today.


PeterH-Airstreamer 12-06-2003 09:33 PM

Dennis, congrats on the onan. Your tenacity paid off!!

swebster 12-06-2003 10:24 PM

I have the manual and schematics....I think the control box is all there is for the "electronics" on the engine side of the genset. Thats how I got it down to the pressure switch and relay. Seems like mine has been electrical all along as it started and ran fine after I cleaned out the carb this past sumemr but then it started blowing ignitions fuses..then fried the R1...I just keep moving upstream.

Maybe it time to replace everything like you did. I also want to get in there with some contact cleaner and make sure all my grounds are clean.

Good job on chasing out the Gremlins. Now if I could get you to look at my fridge! :)

wb13798 12-06-2003 11:32 PM

the model for my gen set is nhe i think. i havent seen a resistor on mine. i passed on the symptoms some time ago when someone was looking at r1 and my repairman says he has never replaced one. his thoughts were if you have a bad r1 you got lots of troubles.
the regulator module is behind the control board. the control board i where the start switch is and the fuse also. and the remote start plug in on one end. some models have a capicator mounted on the module some dont. it is on the bottom of the cavity behind the control board. square cube with several wires coming out of it.
if that blows you can make the genset run by holding the start switch down. the 6.5 will not run if it is not generating ac. has to be generating ac to run. the 7.0 marque series will run all day long and not generate one volt. differeny design.
i would plug a voltmeter into an out let and see if i was generating power before i start rebuilding anything.

swebster 12-07-2003 10:43 AM

Good point. If I jump the relay it'll run and generate AC (I get an AC light on the control panel inside) but I haven't checked it with a voltmeter yet.

I do really need to deal with this soon.

Someone told me once that there is a replacement part number for these old Onans that will ensure that they run forever:



ALANSD 12-07-2003 03:17 PM

There is a pretty basic but usable troubleshooting guide on the ONAN website. I think I posted it here sometime ago, but if not easily found here you can find it there. I weas surprised that an over filling of oil will cause the stalling I was having on turns.

wb13798 12-07-2003 06:37 PM


87MH 12-09-2003 07:32 AM

Thanks, all
Thank you for all of the replies here. Good info.

Now, if we could just get Onan (and Continental, and Lycoming) to design the installation of oil filters so that you can change them without leaving a quart of used oil all over the engine/compartment.

Had some success with manufacturing an aluminum foil funnel to catch the runoff in some instances, but the Onan mystifies me as to how to catch the "filter dribble".

wb13798 12-09-2003 09:28 AM

i stuff the area below the filter with rags to adsorb the oil. works for me.

Jim Tyrney 01-05-2004 03:36 PM

Quick question, when changing the oil filter on the Onan, do y'all add oil to the new filter before installing? Thanks, Jim

wb13798 01-05-2004 04:36 PM

but probably not a bad idea. it would only add to the mess.

swebster 01-12-2004 06:39 PM

Yippee, Yahoo, Hooray!
Finally, finally, finally fixed the Onan. Turned out to be a low oil pressure switch. $7.65 at the Onan store and she was running like a top. Turned on as many things as I could and let her run for a good two hours.

What a relief to have this one checked off on “THE LIST”

Also, regarding oil draining: If you remove the cover surrounding the oil filer there is a "funnel" under the oil filter. There is a small hole in the surround that the oil is supposed to pass through but it just makes a mess. If you remove the shroud then you can fit a shallow pan under there to catch the oil.

87MH 01-12-2004 07:12 PM

One more gets checked off of the list!

Amazing how sometimes such simple things take so long.

At least you didn't have to pay to get it done.

What's next?

Tinsel Loaf 01-12-2004 07:25 PM

Just a note:
Because a resistor or a diode or a piece of electronics checks goods, it doesn't mean it will work in the real world. Replace suspect items and save yourself some grief.

art 01-12-2004 07:54 PM

I have a propane onan generator in my 77 travel trailer any one had any experienece with these .IVe not had it running and owned the trailer for 6or 7 years

swebster 01-13-2004 07:56 AM

No experience with Onan Propane generators at all. I'll bet after 6 years you may want to take it in to a shop for an estimate.

I would suggest a seperate post on the forum about this one. I'm sure there are a number of members out there with these in their trailers.

Also, depending on where you live in NH there is a dealer in Plaistow (CampAmerica) that has a great service manager. He spent about 30 minutes with me on my Generator last summer. They don't carry Airstream but he's an Airstream nut. I've forgotten his name but the General Manager's name is Ric Leather. I'll bet if you called them and played nice with the service manager you would get a lot of free advice to start out your repairs with.

Stripping the interior, building all of the retro cabinetry and new upholstry is the next "BIG" project. Still have on my mechanicals list: Get fridge working on 12V and propage, replace U-Joints and carrier bearings, replace front wheel bearings, replace exhuast with Gibson and get the darn windshield washer pump working. Then follow your lead and polish the outside (YIKES)

All times are GMT -6. The time now is 06:37 PM.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.