RV Generator Question, Billy Shafer

John T

Well-known Member
Billy, Yeah I know you and most are NOT fans of Generac RV Generators, but that's what was in the one I bought and works good EXCEPT for one problem which I want to ask you about. Its a Generac 4 KW Model 4700 in the RV

It starts fine, runs smooth and powers the AC or Microwave or coffer maker or hair dryer all fine, no black or blue smoke, no sputtering, no coughing, nice clean warm gray NON Fouled spark plug BUT after maybe 30 minutes if running the rooftop AC IT SHUTS DOWN........No its NOT out of fuel, NO the ignition system is fine, ITS LIKE A SUDDEN SAFETY SHUT DOWN such as low oil pressure or low oil (NEITHER of which it is I don't think but????) and I suspect it may be a safety thermal shut down due to overheating ??????????? It ONLY shuts down after 30 mins of AC use, when its real hot outside, NEVER any other time and AC works fine plugged to shore power.......

Ever run across a faulty safety thermal limit switch that's opening although it shouldn't ??? Think of reasons for overheating ?? Its clean and free underneath where the screen is where the fan circulates engine cooling air??

What you think is wrong or what should I try ???? Sure I like Onans but this is what I'm stuck with lol. If I cant fix it I will deal with that when the time comes. On several Onans I had the circuit control boards go bad and that's a high dollar fix

John T
 
Put a voltmeter across the thermal switch. If it shows volts when it quits, replace the switch. if it continues, maybe change the airflow to the unit. Jim
 
John T
I know that Onan and Generac. Both had as an option an over heat shut down system. I will check my files. Could you give the full model and serial number. Is it getting plenty of air. Did this just start or has it been a problem. If it just quits then I would guess it has the overheat sensor. They are normally in the exhaust part of the air stream. Could also be mounted on the head or block.

I don't think to much of the new Onan units. Nothing can beat the old CCKs or NH units.
 
Took a wild guess on the 4700. Shows to have a thermal switch down by the oil filter.
Part number G075281
Temp 284 F
Price shows $38.36

From Jack's small engine.
 
Sounds like you need an oil cooler, but that probably wouldn't be easy. Not good for an engine to shut down on high temp and sit, Like Jim said, maybe you could add a fan to improve airflow.
 
Yep that was my first plan. Have my meter handy and soon as it shuts down see if the switch has opened.

John T
 
John, just a thought. Get a radiant thermometer and do a temperature check when it shuts down.
I carry one in our motor home to check the tires with.

Dusty
 
Just a quick suggestion: before you get too excited about buying parts or a new genset, change your oil. Use a different brand than you have been, and don't use Pennzoil. My thought is that you may be seeing oil foaming and loss of oil pressure because of it. That will cause the symptoms you described, and you probably need an oil change anyway. Other thing is, you said your cooling air exhaust screen was clear, how is the intake screen to the compartment? It should be about twice the size of the exhaust but usually isn't. Quick check: run it with the compartment door propped open.
 
Yep the oil in it isn't very old and is full synthetic Castrol Magnatec but I'm gonna change it anyway. I tried it with the RV side door propped open made no difference but I didnt try it with the actual genset compartment door open also,,,,,,,,,,,,BUT I think the fan and air flow and design is intended for that actual door to be closed???

I ordered a new 293 Degree thermal switch, I think original they were 277 or 284 and also a new oil pressure switch as they weren't that expensive and I'm gonna try a different brand of synthetic oil. Hopefully the combination of all three of those might cure it?? If not I will cross that bridge when I get to it

Thanks

John T
 
If it has been working fine until now. I don't think it would be a screen problem. Unless it is blocked for some reason. But worth checking out. Changing the switches would be a good idea. Not that much and would be a good idea. To have spares on hand. You can always test the thermal switch when you had the time. I talked to mister Lumus down here. Has the same generator. It happened to him twice a couple of years ago. But has been running fine since then. I have seen different brands of oil cause problems.

Got a fun Onan down here. The service manual is wrong. Rewiring from 3 phase to single phase. Sensing leads should be on A-B phase. But manual says A-C phase. Among some other problems. Guy wants to spend money on new parts. When all he needs to do is change one wire. But the guy is going to find someone else. Since I don't know what I am doing. I have converted plenty of those switches. But I guess he wants to pay for advice. Maybe I will go fishing.
 
I guess oil could foam causing pressure loss which would also shut it down. I ordered a new 293 DEgree Therrmal, a new oil pressure switch and new Royal Blue full synthetic oil (has Castrol Syn /in there now) and will let yall know what happens

John T
 

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