Onan quits when hot

[CLIFFTALL]

Originally Posted by 2008 Bounder

Well I have the same problem with my Onan 5500 Gold, if I try to run the generator at any temperaature above 90 degrees it quits and give a code 3-36! I change the oil and filter every season, this year I put 30 weight because the guide says to use it for temps over 32 and above. This has been a problem since new (Nov '07) and the dealer replaced the rear AC unit stating it had a dead short (but the unit worked on shore power just fine!) I take it to the dealer and they run it and it works fine at cooler temps!

My 36 code turned out to be the fuel pump.

[sc3283]

if suspecting vapor lock....put the old type spring loaded wooden clothes pins on the fuel line....the more the better....they absorb the heat in the fuel line. This was a remedy for vapor lock back in the late 60s/early 70s on the air cooled VWs for the super hot summer months.....it always worked on them

I'd suggest before and after the Onan fuel pump if it was mine giving me problems

[cb1000rider]

Vapor lock / fuel pump should be pretty easy to determine. Once it misbehaves, pull the fuel line, have a bottle handy, crank it with the fuel line in the bottle. No fuel = vapor lock.

Course, I've got this thing home, cleaned the air filter and I'll be darned if I can get it to misbehave...It's probably because I have it parked under cover, but it's going to be pretty hard to diagnose until I can reproduce...

[mhudson]

Our new to us 2006 Holiday Rambler with Onan 5500 Gold generator started and ran fine for the first hour of our trip Friday. Then... It shut off with the temp about 100 outside. When we arrived about 2 hours later my wife wanted our 5th wheel back!
Same thing all the way home today. Run awhile then throws a 3-36 code. I got home and started checking everything and when I pulled on the connector for the fuel pump the ground side fell off. I think only a couple of strands were holding it together. I soldered on new terminal and it ran with a 32 amp load with all doors closed in the driveway for 2 hours. Just shut it down and will take it out in the heat of the day tomorrow. Hope this fixed it..

[clyon51]

I hope it fixes it too. Can't imagine driving in 100 temps with no AC. There sure has been a rash of Onan failures going down the road this summer and most apparently due to heat.

I have come to the conclusion the problem in these cases are due to the heat from engine/trans/exaust making it's way to the intake cooling air. I would also bet those having heat failures, the genny is in the rear of the coach or, too close to a heat sourse. If I were having this problem, I would take my remote thermometer and place it near the intake air and monitor it going down the road, I bet that would tell a lot.

I had and old C where the Onan was behind the driver and the access door was half opened covered by a large aluminium screen. One year in August in the Badlands, it was 115 degrees and never had a problem.

Me thinks mfgs are not doing their homework lately when it comes to placement of the genny or isolating/insulating from the excessive heat under the coach. Seems to me a $5 plastic duct routed to outside air would fix all this. Just thinking out loud.

[cb1000rider]

Heat source? Shoot, it's 106 out and the temperature above a black road is probably over 120 degrees.

We couldn't deal with the failure either. I bought a back-up genset and put it on a hitch mount.. Then drove home.

I think I'm going to insulate the fuel line, maybe replace the fuel pump. I ran the genset yesterday (temp in the 90s) and had no problems running both ACs, however, this was on a concrete driveway (light color) and the RV was under a steel roof...

[clyon51]

Originally Posted by cb1000rider

Heat source? Shoot, it's 106 out and the temperature above a black road is probably over 120 degrees.

Yep, and if the catalitic converter/exaust and muffler is on your genny side, it could be 200 degrees or more at the air inlet, while going down the road.

[FW5000DRIVER]

Move up to 20W-10 through 50 oil if you will be camping in an area that is in the 100's or expected to be in the 100's. I would assume right now you are probably using 5W-30. If so that is only rated for up to 80 degree's.

[cb1000rider]

I had 15w-40 in it prior. I just swapped it for straight 30 weight oil, which is what Onan recommends for the highest temperature range.

As I'm currently unable to reproduce the problem, I'm doing the following:

1) Replacing all of the fuel line from the fuel pump back. This line is fairly tight in some places, but places where it is not tight, I'm insulating it with heater hose. We just slip the heater hose over it.

2) I'm replacing the Onan fuel pump. Apparently pumps can get weak when hot and although I can't confirm that to be the case here, I'm willing to spend the money on it. From Onan, it's a $120+ pump, but it's made by Airtex. If you can get the AirTex model, it's available at many auto stores. I found one on Amazon for under $40.

3) I'm going to insulate the fuel pump also. It's largely cooled by flow of fuel. I think I can do this with header wrap, but we'll see.

Other coach improvements will be upgrading our AC units to 15k.

[vacation on wheels]

If your like me, you are trying to chase codes when your Onan won't start. Mine is a platinum 5500 fuel injected unit. Turned out I had to replace the fuel line from the fuel tank to the generator. I decided to use metal lines for a one and done repair. It turns out my manufacturer used the wrong hose (non-fuel injected) and my symptoms were sporadic and only didn't work when I REALLY needed it to work. My suggestion is to replace your fuel line to the tank as a precautionary measure, because eventually the hose will go bad, metal lines should last forever.

[cb1000rider]

Not sure why a non-fuel injected hose wouldn't work... Well, until it broke due to over pressure.

I'm currently unable to reproduce our issue if the RV is not on the road. To try and resolve, I'm replacing the fuel pump (I found the manufacturer and ordered one for less than 50% of the onan price). I'm going to insulate that pump with header wrap. I also replaced the fuel line from the pump to the carb. Over that line, I put heater hose, where I'm able to for additional insulation.

I suspect my issue was fuel related as I was getting rpm up/down before the genset shut down.

[FW5000DRIVER]

That is too many 5500 related issues. I has to just be a limitation of the model. It was meant to be able to operate at those temps, but obviously it is not. Time to call Onan?

[clyon51]

Onans can certainly run fine in 100+ degree temps. The problem is when mfgs install them they are not insulated from all the heat being generated by the engine, trans and exaust system getting to the genny going down the road.

[cb1000rider]

I dunno how you do that without putting the generator in front of the motor (IE, DP).
Our MH has the banks system, the exhaust is on the opposite side of the coach. Still, going down the road, you're going to get heat from the motor coming down the underside of the RV.

Looking at Onan manuals, most seem to be rated to 120 degrees. Here's the reference for a 5500 Onan Marquis (Gold): http://www.poweredgenerators.com/ona...als/a-1425.pdf

However, if the air temperature is 106 degrees.. Anyone wanna venture a guess at what the temperature of the road is? Let alone inlet temperature in compartment sitting on top of the road.... I'd wager it's over 120 degrees.