Onan hot hot hot

[onrecess]

I had trouble with my gennie dying for years. I spent a couple thousand at CW, they called in onan twice, kept it for many months. I pulled the fuel pump and replaced it. Runs great. I drove 200 miles across Florida, 90 degrees. No problems. Coming home, I stopped for gas. I shut it off (it exhausts under the fuel filler door.)mWhen I went to start it, no joy. I went to shange the oil. I could barely keep my hands on the cover to pull it. I had to hold the dipstick with a rag, it was too hot too touch. I drove a few minutes to let it cool. After ten or fifteen minutes it started right up. No problems after. I can shut it off and restart, but sitting long enough to fuel up it gets too hot. I looked under it to see where air goes in... There is a perforated metal part where the oill filter and drain is. There is metal plate behind it (touching). There's a pan that covers almost the whole bottom, and the perforated part disappears over that, with a 2" gap the length. Is it open under? I assume there is a fan, is it belt driven? Seems awfully hot. Is this normal? Does your gen set get that hot?

[apr67]

I think I am going to pull the trigger and buy this:

026-00495 SIDE AIR DISCHARGE

https://sleequipment.com/onan-genuine-part-026-00495-mounting-kit-onan.html

Onan also has one that pushes the hot air towards the back of the generator.

[apr67]

CoachFiver wrote:
But we are still either vapor locking or control board is getting too hot and shutting off fuel flow.

What I did to ensure it wasn't the control board. I ran a hot wire from positive to the fuel pump directly. The control board no longer had any power to start or stop the fuel pump. I had the same failure still so I know its not the control board.

When doing this test you have to have a fuse inline, and I put it outside the gen box so I could grab the fuse and pull it quickly to kill the pump. You must be judicious to quickly kill the pump when the generator dies or when you turn it off.

Personally the fuel pump seems to be in a very bad location, it gets no airflow and remains really freaking hot. I might add a 12v muffin fan to get some air to it.

[CoachFiver]

So I ran my sheet metal deflector this weekend, it did help. Temp was high 80's, high humidity with no shade. Generator ran for approximately 2.5-3 hours and then shut down. Took off front cover and scorching hot. Again opened small bolt on fuel bowl, no fuel in bowl. Touched fuel pump, and it is much cooler than before. The area that is under generator where intake cavity is, is much cooler using the deflector. But we are still either vapor locking or control board is getting too hot and shutting off fuel flow. Next plan is to heat tape rubber fuel line where it passes right next to the exhaust side of the generator. When doing some additional testing, the right side of the generator(exhaust side) is where the most extreme heat is coming from while running.(of course that makes sense) And that is where the fuel line connects. In fact the connection of the fuel line is literally a couple inches from the exhaust pipe as it drops down thru the bottom of the generator. Will have to try to get a picture of it with cover off.

[onrecess]

We have been drom FL to Michigan and almost baxk home in the last couple of weeks. I now shut off the air conditioners for 5 minutes before shutoff for fuel. It starts up, though I do have to hold prime 20 seconds or it starts, sputters, and dies. I think there is a slight vapor lock, but it is fine after priming brings in some fuel.
I ran in 90+ temps a lot, and 97 in Mich. Never had a single problem. Map40 abd Down The Avenue hit it right on the nose. Letting it run for a few minutes without ac cools it down enough that a prime gets it restarted every time.

[onrecess]

wopachop wrote:
What a bummer man. You spent a couple thousand at cw and an Onan technician came out twice?

I wonder if there is paper work documenting his Hot Air Recirculation Test? If not maybe you can recoup some dinero.

THAT problem was the fuel pump. They replaced the carb, and then said they were going to rebuild THAT! All it was, the whole time, was a fuel pump. I fixed it in ten minutes, under $100.

[bounder39zman]

I run a mobile generator shop (in the South!), and fight this battle all summer long with Onan HGJAB and HGJAE (commercial version). Several things going on here. 1) fuel pumps get hot and quit pumping, will usually display fault code "36", Control board circuit that powers fuel pump gets so hot it quits sending power to pump, again shows code "36". The gasoline we have now seems to have a lower vapor point, so it is "boiling in gen compartment and carburetor (i.e. vapor lock!). Onan ( Indiana Distributor) has designed and made available several kits to install and deflect hot discharge air away from the cooling air intake. This has helped in a number of cases, and seems to be best solution, short of moving to Alaska. The EFI versions do much better, as fuel is under high pressure from the supply pump, but they too seem to run very hot in high ambient temps.

[wopachop]

Seems like a lot of the newer toyhaulers I see have a open screen over half the compartment door.


We boondock in 110F and often see compartment doors held oven partially with a stick.

Not sure if those people have actually taken measurements to confirm it helps cool the genny.

[joebedford]

One of the problems with the compartment door is that if he's already having problems with airflow, leaving the door open could let combustion products get into the rig.

[map40]

CoachFiver wrote:
If I run my generator with compartment door shut it will shut down in 70 degree weather. There is just not enough of a baffle separating the exhaust side air and the intake side air. Going to try my homemade sheet metal heat deflector this weekend.

The only real problem is the generator cover. It is designed to direct airflow. One of the first times I worked on a generator I was running it without the cover and burned out the exhaust because the airflow cools it down. No cover means the air will follow a different path.
If the problem is with the compartment door that is a coach manufacturer problem and could very well be an issue. All 3 of my Jaycos 31XLs melted the compartment door after 1000 hours. Still, always let the generator cool down running before turning it off.

[CoachFiver]

If I run my generator with compartment door shut it will shut down in 70 degree weather. There is just not enough of a baffle separating the exhaust side air and the intake side air. Going to try my homemade sheet metal heat deflector this weekend.

[joebedford]

Don't run it with the compartment door open or the generator cover off. That reduces airflow and promotes overheating.

[map40]

When you shut down the generator the temperature shoots up because there is no more air circulation and you have a lot of heat in the engine. This stands true in any internal combustion engine.
What I do is I leave the generator running for 5-10 minutes with no load before shutting down so it can cool down and then I shut it down.
If your generator has poor air cisculation, you need to let it cool down with no load while running. I had a 5500 that the previous owner told me to be carefull because he had that problem. Because I was doing this I never had an issue restarting it.

[wopachop]

What a bummer man. You spent a couple thousand at cw and an Onan technician came out twice?

I wonder if there is paper work documenting his Hot Air Recirculation Test? If not maybe you can recoup some dinero.

[apr67]

shastagary wrote:
from the installation manual

Hot Air Recirculation Test A representative installation of the genset must be tested to determine that the genset will not overheat due to recirculation of hot air back into the genset.
8.4 Test Requirement The rise in inlet air temperature over ambient air temperature must not exceed 15°F (8°C). A rise in inlet air temperature indicates hot air recirculation. If the rise exceeds the requirement,steps must be taken to reduce recirculation to an acceptable level.

I am wondering if my multi probe BBQ thermometer is enough for this job, I'm going to try it and see as soon as the rain (cooler weather) moves away. I think the problem is recirculation on my unit with the same exact issue as the original posters.