Onan Overheat Shut Down

[Dick Simonis]

Since my Onan has been shutting down after 30 minutes of running with or without load I'm trying to determine if it truly is overheating or not.  To that end I bought and infrared thermometer and just sat out there with the genny running and took readings at various place.  I don't have a service manual so I'm kind of guessing at the coolant path but the readings are still interesting.  Everything is being observed through the service door.

There is a water hose that runs right along the side of the engine with a tee gong left to some unknown location.  Anyway this water hose was slowly creeping up to ~200F but the small hose going left was about 160F.

The bock right under the dipsitck went to ~220F and the valve covers to 220F.  The oil flter went to 190 or so.

There is a radiator lying flat under the generator end and that got to 240 just before it shut down.  I would like to know what that is.

Again, have no idea what the thermostat is rated for but the 200 or so on the hose does seem high unless that the thermostat setting.

I would love to see a flow diagram of the Onan so I know what goes where but right now I'm thinking that yes it is getting too hot.

If any one has some thoughts, I would love to hear them.  I will be taking it into a shop this month for a complete 1,000 hour service but I would like a better idea of what i'm dealing with before I start calling around.

This did happen fairly suddenly since we had it running at BCS for hours and only started acting up on the drive home.

[Steve Huber Co-Admin]

Dick,
The radiator lying flat on the bottom of the geni is just that. Manual says over-temp shutdown occurs at 239 degrees for 10 seconds so if your radiator read 240, you were in an overheat condition. Possible causes include dirty radiator, low coolant level, faulty thermostat, or bad belt.
I'm emailing you a manual set.
Steve

[David T. Richelderfer]

I had the thermostat, belt, and heat sensor replaced about New Years in Lake Havasu... 10 months ago.  The generator worked well until I got nearly back home in March.  In March the generator again developed a problem where it would shut down with an overheat condition.  BCS found two problems 1) bad crimp-style tighteners on the hoses, and 2) some sludge like goo plugging up the small hose attached to near the fill cap.  The crimp-style tighteners came loose and allowed coolant to escape.  If you get into the machine, then I would suggest you replace the crimp-style tighteners with screw-type tighteners.

[Edward Buker]

Dick,

I believe that you have an overheat condition and most likely the belt is bad. There are some infrared readings I have taken on my genset in both an overheat and normal operation in this post as a reference. I also included some air flows with a hand held anemometer.

http://forum.bacrallies.com/m-1302907037/s-11/highlight-anemometer/#num11

Later Ed

[Dick Simonis]

 Steve and Ed, thanks for the info, it was very useful.

Tentatively I have made the decision to have the genny serviced at Premier Motor Coach in Tucson.  I spoke with Erik today and he advised I just go ahead and have it pulled since it would be much quicker in the long run to do everything in the shop.  He said they can pull, replace everything and re-install in 4.5 hours.,,,,that doesn't seem bad at all.  He also suggested to replace the water pump as long as it was already out which also made sense.  It has 1100 hours so this service should do for as long as I will own the coach.  Excluding oil changes of course.

[Steve Huber Co-Admin]

Dick,
Good luck. Eric and his crew seemed knowledgeable and competent at the Kerrville rally.
Steve