generator and gas mileage

Whether or not roof air, with its gas engine to generator to motor efficiency losses (about 20-35%) is better than dash air, with only mechanical (10-15%) losses but sized to 3-4x capacity, for fuel consumption, is largely irrelevant.

If you want to cool the house, run the genset and roof air. Air from the dash won't really cool the house.

If you want to cool just the cab, run the cab air. It will draw 10-20 HP for the compressor, intermittently (it disengages according to load and demand) but feeds a correspondingly higher capacity cooling system that is just not plumbed to cool beyond the cab. If you want to cool the house, you would bring the cab down to winter temperatures.

Only caveat, if running dash air raises underhood temperatures high enough to engage the engine fan at highway speeds, that fan will cost you another 20-40 HP while engaged. It is designed for intermittent use in slow speed traffic, any other time it engages you have an engine cooling problem.

THERE is a theory that says the use of the generator will actually be more cost effective than relying on the engine.
If Jenny is on the A/C compressor on the engine can be off lessening the load on the engine and increasing performance, lowering heat buildup and increasing fuel economy. As a bonus the fridge then runs off of the 110 volts from the Jenny conserving propane.
My guess is the cost factors are pretty even in the long run so why not enjoy it and be comfortable

I live in Florida and run with the generator/roof air on most of the year.I've been told and believe it's more economical to run the generator with its .5-.7 gal per hour usage than it is to run the dash air, along with its engine mounted compressor.
It relieves some of the load /strain on the MH engine. Your engine could also run a degree or two cooler. In my case there was a noticeable difference in my first class C. It was a 22' Four Winds with a 5.7L GM engine. Whenever I ran with the dash air on (and more noticeable if I was towing a boat) the auxiliary engine fan was constantly engaging, which wasn't the case if the dash air wasn't running.

Thanks for all the input I appreciate it. We just bought a 1993 fleetwood jamboree 27' with the efi 460 engine. It has 43, 000 miles with an onan 4000 generator.

Does anyone run their generator while driving and if so how does it affect your fuel mileage? We are planning a

trip to florida in august.

First of all I feel for you. Driving in a MH in Florida in the middle of their hot summers is brutal at best. :B

Do yourself a favor and pick up a bunch of van windshield shades and put them in your cab over window and side windows when traveling. That will bring the temps down inside your MH about 20 degrees. And cover your roof vents with those pillow inserts again helps to keep the heat out.

Regarding your mpg question:
I think it is a push when compared to running the dash air which actually is harder on your engine in hot summer heat in the southern states. I don't use the dash air that puts the compressor on, etc. Drops your mpg and heats up your engine.

I have a gas gen and when I first started out and really cared about what mpg I was getting I found it to be the same as when you are running your dash air.

Take just one trip in your MH driving in the southern states during their summers and you won't care if you are only getting 2 mpg with the coach air on! :B

It will cause you to use an additional .5 gallons per hour. How that impacts MPG depends on how fast you are running.

If you are using 8 gallons per hour to run 60 MPH (7.5 MPG) then the additional .5 gallons reduces MPG to 7.05, not quite 1/2 MPG less.

If you are using 5.5 gallons per hour to run 50 MPH (9 MPG) then the additional .5 gallons reduces MPG to 8.25, about 3/4 MPG less.

If you are standing still running the generator, MPG is reduced to zero, because none of the fuel being used moving you.

We have a 96 Southwind on a P-30 chassis. I run the Onan 5500 generator and roof air while driving.
I don't think it uses any more gas than running the dash air.

Fire up your generator while rolling down the road and keep your unit cool. It will not hurt the generator to have it running while driving.
And, I doubt you will notice much change in gas mileage.

We use ours when it is really hot outside. I wouldn't mind if it doubled my fuel consumption if it keeps the DW happy I am happy. But in answer to your question I haven't seen a large increase in fuel usage. JMO

I run both a/cs while traveling. Keeps my kitty cats happy, lol. Doesn't seem to have much of an effect on the mileage but doesn't really matter...we're going to keep cool.

Cat Lady

Welcome New Member.

It would be helpful if you would post the make of the generator. Size, Gas or Diesel. Also how many air conditioners? All of this will have an effect on mileage.