Fuel mileage of Diesel engines

[CP194849]

I'm in the process of shopping for a used diesel pusher. Would appreciate input on the following: All things being equal GCVW, etc, is there a substantial difference in fuel mileage between a larger engine I. E. 400 to 500 HP and a 300 or 330 HP engine

[bluwtr49]

Good point on the fuel expense.

Our typical 4+ month "Summer Sojurn" approx costs:

Fuel: $1800.00
RV Park: $3600.00
Food: $1800.00
Golf: $3000.00

And worth every penny.

Of course from that we subtract costs we would be incurring even if we never left home. So the fuel is kind of incidental to the whole summer thing. While it's nice to know what the fuel cost would be for budgeting purposes, the MH experience does have some expense associated with it. IMHO, the fuel cost won't change significantly if you have a MH, TT, or 5er....they all come in at roughly the same.

[blakduk01]

This has long been a favorite idea of mine. I think everyone knows that the power to weight ratio is key to mileage. I have a 2000 'A' DP.
It has the sloping front cowl.

I think it has the 300 HP Cat engine with an Allison tranny. I consistently get 10mpg whether empty or towing my Nissan "Juke" or my
"PT cruiser ragtop". Now in a previous post someone mentioned thatthe dealer would not let you have a larger engine in a smaller unit. I have checked into it because right no I could not afford to, but if I ever have the opportunity I feel that if I got the 500HP engine and put it in a 38ft rig I could possibly achieve 11-12 mpg. Carrying it a bit
further with a Banks exhaust system maybe even better. I am sure that as long as I am willing to pay for it, the manufacturer would build it for me.

Any thoughts??????

[Fishinghat]

All the posters gave very good answers.

In summery, it comes down to how you drive and that will make the biggest difference.

But, you know what? Your fuel bill for the year will pale in comparison to your depreciation. If you add maintenance, insurance, license, etc., fuel economy is a very minor cost factor in the "price of ownership".

[discovery4us]

5.9 cummins, 275 HP, 25,000 LBS. coach, 6 speed Allison

11 -12 solo
9 - 10 with wrangler toad

[bluwtr49]

Diesel engines are actually rated at lbs/hp fuel consumption. You can get that rating from the manufacturer than back calculate how much fuel will be consumed based on the wt of the coach and the speed you're driving.

The kicker here is that diesel has a fairly wide density spec so the fuel alone will change the mpg by several percentage point with all else being equal. If you factor in winter blends of #1 and # 2 it gets even worse.

So....the upshot is that the HP rating of the engine makes little difference, how much of the HP you decide to use is the key factor.

[Peralko]

In the same motorhome there may not be that much difference in mileage. But if you are comparing a 38-foot motorhome with a 400 HP engine to a 45-foot tag axle equipped coach with a 525 HP engine, there will definitely be a difference. The increased weight will have a lot more impact that just the size of the engine.

[Executive45]

We get 9-10 mph depending on whether it's pushed or not. The larger the engine the less it has to work. Climbing to the Eisenhower tunnel to 11,800' we downshifted to 4th only once, rest of the time it was in 5th @ 1350 rpm...Dennis

[Tom_Barb]

Our Cummins 350 ISC with a chip to 400 will give us 9.5-10 mpg, when we drive 60 and put the transmission in economy, and let the computer drive it.

[RayChez]

What a lot of people forget is that manufacturers install diesel engines according to weight. If you have a heavy coach, you are going to get a five or six hundred horsepower engine. If you get a light weight coach, lets say around twenty thousand pounds, you are going to get a small diesel like a 5.9 Cummins. But you will not see from the factory a light coach with a big monster diesel. It just does not happen.

So diesel engines on the average will get anywhere from six to nine miles per gallon of diesel.

Now there were some two cycle DD engines like my buddy has on a Bluebird which weigh's 45K lbs and it only gets five miles per gallon of diesel.

Larger diesel engines are installed to move more weight. So it all evens out in the end.

[country_sunflow]

Our 350 diesel pusher gets 8.5 mpg. We are very happy with that because the gas 454 only got 5 mpg.

[Yaj]

I have the little 230hp 5.9 Cummins. If I take it easy I can get 11mpg. I'm pretty happy with that.

[wolfe10]

For a given weight and driving style, there is little MPG penalty on a diesel with more HP. Larger diesel, lighter throttle for same power. Remember, diesels can run on a lot of air and little fuel if not pushed.

But, most with that extra HP USE IT.

[rexabbot]

crasster wrote:
Just keep in mind the diesel costs more, if that is your concern. It evens out.

OP was only asking about diesel

[crasster]

Just keep in mind the diesel costs more, if that is your concern. It evens out.