rooftop air

tucsontattoo · May 09, 2006, 01:07:38 PM

Drivingmisslazy
Thanks for the input> I have a 4 KW Onan (air cooled) running on propane. All other propane app. in the coach run fine. Gen. will not start or continue to run while moving. Cannot duplicate the problem under any stationary conditions.Any ideas?

?

JackConrad · May 09, 2006, 02:26:24 PM

Perhaps bus aerodynamics are causing a reduction in air flow across the generator when running, causing the overtemp switch to shut down the generator? Cooler day would allow it to run longer before shutting down. Jack

tucsontattoo · May 09, 2006, 03:29:20 PM

Hummmmmm just might happen, will look into it!

Greg

tucsontattoo · May 09, 2006, 04:00:15 PM

Nope not an over heat thing, Won't start while moving with the gen dead cold. Gonna keep lookin.........

NJT5047 · May 09, 2006, 07:28:30 PM

How long after you're driving does it shut down? When it won't start, is it turning over and not lighting up.....or does the starter not turn the engine?
Where does your liquid line exit from the LP tank? Out the top of the tank? Have you tried topping off the LP tank?
Is anything electrical running off the genset when it shuts down?
Jack seems to offer the most plausible idea so far...there have been liquid cooled gensets that wouldn't cool when driving at highway speeds...the airflow thru the radiator was "reversed" or "cavitating" due to aerodynamics of the bus body when underway.
I assume that there are no valves or solenoids in the generator line between the LP tank and the generator? The liquid line may have a faulty pickup, yet the "vapor" RV appliances are fed with another line and would continue to work. If the liquid line surged or slugged vapor, the engine would quit. If a solenoid cut it off, the engine would still run for a good bit before it ran out of fuel. This is a liquid LP unit?? As opposed to a vapor gas unit. I believe we covered this early on.
Are any removeable bus body covers that are convering the generator? The genset box factory covers must remain in place to cool correctly. If no solenoids and the LP tank is 75% or better, I'd put my money on heating.
While you may not wish to fool with this idea, but maybe a line could be attached to the overheat switch so that it's function could be monitored from some vantage point inside the bus. Could be the generator head overheating and shutting the engine down...? Not sure that Onan has overheat protection on the gen head.
Be gone for a few days...expect to hear that this problem has been resolved when I return!
Stumped, JR

NJT5047 · May 09, 2006, 07:38:03 PM

Just one more thing...if this is a liquid line genset, do any of the LP components require accurate barometric pressure (converter, regulator?) to function? Someone familiar with liquid line small engines would know the answer to this. The airflow thru the generator box may be affecting such sytem components. My guess would be that the baro pressure would be significantly reduced when underway. This would be especially true if the unit is behind a large mudflap.
If the unit won't start, but turns over at highway speeds....try sealing up the generator box completely so that the bus airflow cannot act on the LP components...try starting it. If it starts...viola...if not, forget this tack. If it starts, the point is made, turn it immediately off before it heats up. This seems to have been a problem from the gitgo. Was this a professsional conversion, and if so, is the converter still around??? Or any of their conversions with similar generator setup. May be some interesting history.
Best, JR

tucsontattoo · May 11, 2006, 08:51:14 PM

OK.... Here is the latest When I got the bus the fellow I got it from had re skined the doors on the bays doing away with the intake grill for the gen set bay.Figured with the bottom of the gen box open it wouldnt matter. Add to that picture the fellow who built the coach thought it would help his cooling to leave the bottom of the sound box wide open.Then.....somewhere along the way someone added a fome filter cover to the air cleaner element NOW... I start the gen set, turn on the ac's and drive down the 2 lane about 45 or 50 all is well... Hit the interstate and bring her up to about 60 still running fine. Push her over in the fast lane run her up to about 65 and no more gen... I was pulling a vacume on the sound box with a restricted air intake, so the vacume accuated propane regulater feeding gen engine shuts off fule to engine.....That is what it was.Not movtng, just moving fast!!! Fianly figured it all out, Couldn't have done it with all the thoughts and mabie its the kinda input you guys came up with, Thanks so much for all your help. Goterdone

Greg

FloridaCliff · May 12, 2006, 05:10:55 AM

Greg,

Excellent news and good troubleshooting.

Its always an extra challenge when you have to unfix what others have fixed.

Cliff

tucsontattoo · May 12, 2006, 09:37:50 AM

Amen to that Cliff, Thanks to Jr's input and your input I was able to move through all the possibilities allot faster. What really got me thinking was an old picture of my bus before the new door skins were installed. I think the final fix will be to have louvers cut for the cooling air intake and I'm going to plumb the engine (gen set) air intake through the sound box wall so I'm drawing intake air from inside the bay and not from inside the sound box.

Greg