Generator overheating

[jrm1776]

First I need to get our Cummins generator running again after purchasing 2 new auxiliary house batteries. We took a road trip from Tennessee to California back in 2016 and I believe had overheating issues on this generator so we could not run the rooftop A/C and my family was burning up. We got out of hot climates into California and it would be good to go since it was under 100 degrees. Then we left to come home, soon as the thermometer on the dash popped 100 degrees, the generator shut down again. I've had people tell me "just drive up north more".... seriously? I see motorhomes driving in the summer months with 2 rooftop A/C's and parents have one that runs in hotter weather with no problems. Is it just this brand or model or do others seems to have overheating problems with their generators too? Yes the maintenance has been completed before that road trip and other times. If somebody else suggest a different generator that is monstrous power and doesn't act like a whiny B, let me know please and thank you.

JRM1776
Tennessee

 

[Isaac-1]

If you were to tell us what brand and model it is we may be able to offer some pointers. For example on my model of coach a common generator problem is vapor lock caused by the way Monaco / Safari routed the generator fuel line parallel and above the exhaust pipe. Many owners including the previous owner of my coach re-routed the generator fuel line to reduce this problem. Another common problem is the hot air from the fan gets recirculated into the inlet due to poor mounting arrangements, I have this problem too when running the generator in hot climates when the coach is not moving, I have added an air deflector to hopefully help with this issue

 

[jrm1776]

If you were to tell us what brand and model it is we may be able to offer some pointers. For example on my model of coach a common generator problem is vapor lock caused by the way Monaco / Safari routed the generator fuel line parallel and above the exhaust pipe. Many owners including the previous owner of my coach re-routed the generator fuel line to reduce this problem. Another common problem is the hot air from the fan gets recirculated into the inlet due to poor mounting arrangements, I have this problem too when running the generator in hot climates when the coach is not moving, I have added an air deflector to hopefully help with this issue

I know it's a cummins, I'll have to get more information from it when I get home today. The problem on our roadtrip was actually shutting down while driving down the interstate. it always started up just fine and when the temp hit 100, shutdown. I always though enough air was getting to it because it's under the coach catching the breeze going down the interstate.

 

[Gary RV_Wizard]

Possibly a poor job of installation of the generator in the motorhome, e.g. the examples in Isaac's reply. Most gas generators are air-cooled and need a path for fresh air to flow in and over the genset. Diesels are typically water-cooled and use antifreeze coolant, but they still require air flow through a radiator. Some alternative issues could be lack of coolant in the radiator, dirty radiator or air screen, or even a faulty temperature sensor.

It would help if you identified the model of Cummins/Onan genset and the coach year/make/model.

 

[jrm1776]

Possibly a poor job of installation of the generator in the motorhome, e.g. the examples in Isaac's reply. Most gas generators are air-cooled and need a path for fresh air to flow in and over the genset. Diesels are typically water-cooled and use antifreeze coolant, but they still require air flow through a radiator. Some alternative issues could be lack of coolant in the radiator, dirty radiator or air screen, or even a faulty temperature sensor.

It would help if you identified the model of Cummins/Onan genset and the coach year/make/model.

Will do as soon as I get home today, that all makes sense too. I'm definitely opting for a diesel pusher next purchase.

 

[jrm1776]

wife sent some pics of the model/type generator. It needs maintenance and overhaul but it was shutting down when it got to 100 degrees outside when it was only a year old. We'll probably take it down to one of our local shops that we trust but just wondering if anybody ever has a generator shutting down on them in the Summer

 

[Utclmjmpr]

Well, it's definitely an air cooled genny,, and at 3600 RPMs its working hard with an overhead A/C.. So it's probably an air movement issue,, oil issues can also be problematic as it helps with cooling.>>>Dan

 

[jrm1776]

Well, it's definitely an air cooled genny,, and at 3600 RPMs its working hard with an overhead A/C.. So it's probably an air movement issue,, oil issues can also be problematic as it helps with cooling.>>>Dan

Thanks for the input. I'll do some research and see if there is any other types to replace this with. I had some oil spitting out somewhat and we got it looked at and replaced gaskets. I'd actually like most of the RV running off of the main instead of needing the generator on while driving just to have the overhead A/C on. I would think it would be ideal to not need the generator until you're parked for the evening and don't have 30/50 outlet like you're out in BFE with nothing in site, then you need your generator.

 

[jrm1776]

I just thought it was odd once this issue started, "Why can't we have the A/C running w/o the generator" - anybody else have rigs with overhead A/C's and run them with no problems in the summer?

 

[Mark_K5LXP]

From the Onan manual:

Gen Set Performance Air Conditioner Starting: (60Hz - Gasoline) One 13,500 BTU air conditioner with 2000W baseload at 500ft (152.4M) and 100F (38C).

Ratings apply to altitudes up to 500ft (150M), 85F (29C) ambient with muffler, in RV enclosure.

What I read into that is the generator can start, but may not necessarily operate an air conditioner above 85F depending on the load particulars. Max ambient operating range is shown -20F to +120F but does not specify the derating above 85F, though derating is clearly implied.

The hottest I've run mine is 108F ambient and it did fine, but I have no idea what the exact A/C load was.

Mark B.
Albuquerque, NM

 

[Utclmjmpr]

You certainly can run your A/C without the genny,,,BUT you better be plugged into a 110 out let OR ,,have one hellofa huge battery bank..>>>Dan

 

[jrm1776]

From the Onan manual:

Gen Set Performance Air Conditioner Starting: (60Hz - Gasoline) One 13,500 BTU air conditioner with 2000W baseload at 500ft (152.4M) and 100F (38C).

Ratings apply to altitudes up to 500ft (150M), 85F (29C) ambient with muffler, in RV enclosure.

What I read into that is the generator can start, but may not necessarily operate an air conditioner above 85F depending on the load particulars. Max ambient operating range is shown -20F to +120F but does not specify the derating above 85F, though derating is clearly implied.

The hottest I've run mine is 108F ambient and it did fine, but I have no idea what the exact A/C load was.

Mark B.
Albuquerque, NM

Well..... that is good to know. Thank you. I read through our manual and don't recall seeing this. Good information I'm learning as I'll find something out there that can run higher with the air hitting it underneath the camper/// Also maybe only take trips in the fall and spring when it's cooler. Might even see about getting the A/C running off the main engine and not rely on the Genny

 

[jrm1776]

Makes me wonder if a diesel pusher is the way to go. Seems like a lot of people like these better than gas rigs

 

[Mark_K5LXP]

Just found this too in a different Onan guide:

Power decreases in extreme temperatures by 1% for each 10° F (5.5° C) above 85° F (29.4°C).

Just for the sake of discussion, how do you know the generator shut off due to overtemp? Did you get a diagnostic code from the indicator light or are you just associating the ambient temp to the genset shutting off?

As an anecdotal point, I'm a mile high here and 108F in near zero humidity, and mine still ran the A/C going down the road. So while that's no guarantee of performance in every installation, it's a data point that it's at least possible.

Mark B.
Albuquerque, NM

 

[jrm1776]

Good question. I don't recall an indicator light. I'll have to research this and talk with my wife because I was driving every time. If I remember right, she said she was seeing flashing indicator lights but I don't remember if she saw any codes. I just remember the A/C shutting down when the outside temp hit 100 on the dot. Wife went back to see if she could get the A/C cranked back on and it would not start. We rolled into California with cooler weather down in the 70's and 80's and it came back on and running fine the whole time we needed it. Then we left to come back home, temp hit 100, boom, shut down again. We were plugging fans into a power strip connected to an outlet on the dash and them crowded around the driver area trying to stay cool.

 

[jrm1776]

Wife just e-mailed me back when I told her about this thread and valid point she has:

Same thing happened going down to Florida.
There is no thermostat on the generator but it sure does shut down when it is hot.
Kinda defeats the purpose of a generator that cannot handle hot temperatures here in the US!

I'm really going to look into seeing if the A/C can run while driving and not ran off of the genny

 

[Larry N.]

I'm really going to look into seeing if the A/C can run while driving and not ran off of the genny

Keep in mind that the house A/C runs off of 120 VAC, so you'd have to feed it with an inverter (much larger than you would have on board) to run from the batteries (unless you have a loooooooonnnnnng extension cord ) and that would require a HUGE bank of batteries, just to run for 15 minutes or so. That's why the genny is needed to run the A/C. Otherwise the electric power available just isn't sufficient, by an order of magnitude or more.

As others have indicated above, there may be some problem with your particular installation, but generally those generators run fine even at 110º+. So it might be cooling air flow (amazing how small a change in that area can goof you up), as others have indicated, oil system problems, etc.

anybody else have rigs with overhead A/C's and run them with no problems in the summer?

I've had three motorhomes with the overhead A/C and all ran fine from the generator. My gas Bounder (34' rig) had two A/C on the roof (air cooled Onan much like yours), my diesel Beaver had three (a 45' rig) and my current diesel Newmar Ventana has two (38' rig). All have done fine on even the hottest days, whether Arizona, New Mexico or wherever, including more than 100º.

Finally, if you DO find a way to run the A/C on the road without the genny and for any length of time (say 5-6 hours driving time) we'd love to hear about it -- that could be a big benefit for us all.

Good luck...

 

[jrm1776]

Keep in mind that the house A/C runs off of 120 VAC, so you'd have to feed it with an inverter (much larger than you would have on board) to run from the batteries (unless you have a loooooooonnnnnng extension cord ) and that would require a HUGE bank of batteries, just to run for 15 minutes or so. That's why the genny is needed to run the A/C. Otherwise the electric power available just isn't sufficient, by an order of magnitude or more.

As others have indicated above, there may be some problem with your particular installation, but generally those generators run fine even at 110º+. So it might be cooling air flow (amazing how small a change in that area can goof you up), as others have indicated, oil system problems, etc.


I've had three motorhomes with the overhead A/C and all ran fine from the generator. My gas Bounder (34' rig) had two A/C on the roof (air cooled Onan much like yours), my diesel Beaver had three (a 45' rig) and my current diesel Newmar Ventana has two (38' rig). All have done fine on even the hottest days, whether Arizona, New Mexico or wherever, including more than 100º.

Finally, if you DO find a way to run the A/C on the road without the genny and for any length of time (say 5-6 hours driving time) we'd love to hear about it -- that could be a big benefit for us all.

Good luck

That's very informative, thank you. Glad to be in this group and getting wife to sign up. We'll be a better team together to hear from all the "more experienced ones"

As far as the dashboard A/C compared to the Overhead A/C, must be different amps. My thought was having the overhead connect to the electrical system through the engine block but I guess that's absurd. IDK... Not a very new noob, but kind of a noob with these coaches

 

[Utclmjmpr]

Even dash air in most cases in a M/H isn't all that effective because of the large windshield and the length of the rig dissipates the cool air with hot air.. Some have had better outcomes with dash air and a fabric "wall" ( curtain ) stretched from wall to wall behind the driver and passenger area. So most will run at least the forward AND the dash airs together on the hottest days..>>>Dan ( Back to the generator again.)

 

[Mark_K5LXP]

I asked about the trouble code because I'm not aware of a general "overtemp" that shuts the engine down on the microquiets. Before I went down the road of alternative A/C solutions I'd figure out what this unit is complaining about first. It may be a relatively more simple, quicker and inexpensive issue compared to an R&R.

How to Read Onan Generator Fault Codes (Cummins Blink Code)

Mark B.
Albuquerque, NM