Amazing Fuel MPG

[Pmedic4]

Seems like everyone I talk to regarding their tow vehicle, regardless of Gas or Diesel, is how good their MPG is for their vehicle.

With my truck, I average about 15-16 mpg overall when not towing, and then when I was towing a 24 ft TT, it dropped to about 8 - 9 mpg. The good news is when I went to a larger 5thwheel, it went up to about 9-10. Other than wind resistance, I can't explain the difference. This is with a 5.7 Liter Hemi Dodge.

Otherwise, my personal experience with GAS versus Diesel has been working on Ambulances and farm equipment, and how much fuel you use in those vehicles. Where I really notice the difference, is when you sit and idle in an ambulance - which is most of the time, since you have radios and computers(GPS) running all the time, the Diesel wins without a doubt. It seems like on a long standby, 4-6 hours, with the Gas engine ambulances we'd use as much gas as if we drove 300 miles ( common trip). Where the diesel ambulances would only sip a little when idling, but get about the same mpg as Gas when actually driving.

Seems like I hear when towing the diesels get the better mileage, but this doesn't seem to match my personal experience in ambulances? There are some differences based on the government requirements for engines in Ambulance, so that could be part of it, but I don't see that much difference in size/weight ( By the way, the legal requirements for ambulances are in section KKK of the DOT code - Don't ask me why KKK?)
Anyone have personal experience?

[xaugievike]

I towed an 8k-ish pound TT for 4 seasons with an 06 Chevy gasser. I'm starting my second season with my 325srx and my 06 duramax. I keep fuel records religiously (which I don't have in front of me, going by memory ill be pretty close - off a tenth or two))

My gasser towing average was high 9's. unloaded average was 13 on the nose. Best unloaded tank ever was 15.9.

Diesel towing average so far is mid 11's. best tow run was three weeks ago with a hell of a tail wind at 13.6. Unloaded average right now is low 16's with a best ever of 21.2

[mhs4771]

While wind resistance is a major factor with either gas or diesel, I think weight will come into play more with gas then diesel. Had a 24' TT pulled by a 350 cu in Chevy Heavy Half 1500, got around 8 to 10 on a good day. Traded up to an 05 K3500 Dually Diesel and got 10 to 12. Upgraded to a 30' TT and mileage stayed about the same, then went to a 34' 5er at double the weight and mileage still stay about the same. Now towing a 41' 17K 5er with an '11 K3500 Dually Diesel and still getting 9.5 to 11.5, with 15 to 17 around town, and 17 to 20 on the open highway.

[ktmracer]

A gas engine under towing suffers a few things that impact towing mpg.
1) with higher throttle openings, and higher load the amount of ignition advance you can have w/o detonation decreases. the more advance, generally the better the mileage
2) frictional losses are related to rpm squared, so the higher the rpm needed, the higher the frictional losses

with the newer engine designs that have variable valve timing, gas engines are developing more low end torque, that helps on (1) and (2) above by allowing lower rpm and higher vacuum.

Diesel advantage include more btu/gallon, more low end torque, unthrottled engine so lower pumping losses, and the fact that the diesel combustion cycle is noticeably more thermally efficient than the spark ignition cycle engine.

Routes that include much hill climbing will likely show a bigger difference in mpg between gas and diesel than level ground. Even on 6 or 8% grades, I seldom need more than 2500rpm and part throttle to make a climb. Gas in most cases will need more rpm and more throttle both of which really hurt mileage.

IMHO advances in gas engines has likely improve the gas towing mpg, and when cost of fuel is taken into account, the difference in cost/mile may not be near as much as years ago. But, In my experience diesel still has a towing fuel advantage, and an advantage in normal driving.

I certainly was getting way worse mileage when towing with a gas van than my diesel truck, but the gas engine was also much older.

I prefer a diesel for towing, but IMHO it's one of those things you do because of what you like, not because it can be justified economically. It would be a hard job for me to justify a diesel engine on an economic basis anymore. You'd have to tow a lot of miles/year for it to pay off.