Onan 7.5 diesel generator

[60 Seconds]

I have a 2006 Journey (52K miles) with a 7.5 Onan (Cummins) diesel generator. Only has 150 hours. Recently it would shut down after running for about 20 minutes. Then, less and less run time before shutting down. I checked the coolant level, it was just at the cold mark, so I topped it off to the hot mark. No change. Oil level was full. I figured it was time for service. Primary code was 1 and secondary code was 33 (overheating). Did a oil and filter change, fuel and air filters as well (genuine Onan parts). Everything looked clean underneath, no nests or obstructions. No dirty or gritty fuel came out of the old fuel filter, chassis engine runs strong. After service it will only run for 60 seconds and shut down. I tried with the breaker on and then off. No difference. I have good air flow across the radiator (I can see squirrel cage fan spinning) and good air flow out the rear. Plenty of exhaust pipe pressure. I could hold my hand on the exhaust pipe b/c if doesn't run long enough to even get warm. For the short time it does run it's really quiet, which it always has been. No knocks or unusual noises. I took the caps off the coolant overflow and the fill cap. I wanted to eliminate any chance there was a vapor lock(?) in the water jacket. No bubbles or burbs. I also had no visible coolant leaks or puddles under the unit. At this point I'm thinking the coolant sensor. For that, I have to jack up the front end of the coach and unbolt/lower the generator (not a slide out type). Big job. Is there anything else I should try before forging ahead with removal?

 

[60 Seconds]

Should add that it runs almost exactly 60 seconds before shutting down. Could that be the time out for a faulty coolant sensor?

 

[redbaron]

Fuel pump or temp sensor are my primary suspects.

 

[60 Seconds]

Fuel pump or temp sensor are my primary suspects.

I'll try disconnecting the return fuel line, place it in a glass jar and hold down the stop/fuel prime. See what volume I get and check for air bubbles.

 

[Swipular]

Mine was overheating and would run for a few min then shut down. Replaced the temp sensor and thermostat and that resolved the issue.

 

[60 Seconds]

I disconnected the return fuel line, had the wife hold down the stop/prime rocker switch. I got a steady flow, no air bubbles, took 2 1/2 minutes to pump a pint of fuel. I believe that's within specs (.4 pint per min.).

 

[60 Seconds]

Got the generator out of the MH. I used an ATV jack. I pulled the coach's front wheels up on double 2x12s (which gave me room to work a little more comfortably)and disconnected all the bolts and fittings before lowering the jack. I then raised the front end up using the camper's hydraulic jacks with a good base of sturdy 6x6s under each jack. This took the guess work out of how high I needed to go to get the proper clearance to roll the generator out. I tested the coolant sensor and got 11 ohms which validated that this was most likely the issue. I believe it should test out in the 60-70 ohm range? I ordered one online and waiting for delivery. I drilled a 2 inch hole in the fiberglass heat shield to allow for a 19mm 6 point socket to come in at the proper angle. I rocked the sensor slightly clockwise and CCW with a breakerbar. It was freeing up so I turned it all the way out but the non threaded end of the sensor, which encapsulates a spring, broke off inside the housing. Luckily I was able to extract it by working it with a 25/64 drill bit. It's brass (or copper) and soft. Before that I pulled the thermostat housing and thermostat and packed the throat with a rag in case any of the shavings entered that area. I got chased inside by the rain. When the sensor comes in, and the rain stops, I'll post some pictures of the reassembly.

 

[redbaron]

That sounds like a very scary situation. I once broke a spark plug on my Chevy. Wasn’t thrilled with the prospect of extracting it but was able to do so much cleaner than I thought.

Glad it worked out for you.