Why such dismal fuel mileage??

[muskie hunter]

I know what everyone is going to say about not expecting high mpg while towing but this is different.
I have a 1996 wellcraft excel 26 se cruiser w/an aluminum trailer. total weight loaded for a trip is about 9500 lbs. I pull the boat w/ a 1997 GMC yukon 2dr with the vortex 5.7 3.73 gears without the boat I get 17, with the boat behind it I get 8.
Now I borrowed my buddies 2001 ford f-350 7 liter turbo diesel 4.10 gears for a run from ohio to lake michigan last week. He stated the truck unloaded gets about 18 mpg,and that I should expect about 14-15 while towing the boat.
I could not believe it when after 1000 miles the truck averaged 8.2. Not only was I in shock.. the truck owner was shocked also. He said he never got that bad of mileage while towing anything. Granted it pulled much better than the yukon,but I would have expected much better mileage from it also. The truck was run at 65-70 mph and the tach was showing 1800-2000 rpm. Are all diesel trucks going to get this bad of mileage? I can understand the Yukons bad mpg because it its getting the tar worked out of it, but not the F-350.
Any ideas or input?

Thanks Steve

 

[mthieme]

Re: Why such dismal fuel mileage??

That's a heck of a difference.
My setup is lighter than yours with less power and I easily notice the fuel consumption difference...never measured it though (broken odometer).
However, whenever I tow heavy or long, I borrow a friends Dodge diesel dually.
I've measured the mileage towing 7000# with it at 80 mph and came up with 19.7 mpg.

 

[Gary H NC]

Re: Why such dismal fuel mileage??

The diesel should have got a little better than that.
We have Chevy and Dodge 3500s at work.We tow around 9000 to 12000 pounds and they get average of 10 to 12 mpg.
One thing with the boat though is it has much more wind resistance than any other kind of trailer.
My Chevy Tahoe gets 9mpg towing my camper and about 10mpg towing my boat.

The Dodge trucks seam to get a little better than the Chevy trucks.

Gonna play you got to pay is the way i look at it.

 

[WhereBob]

Re: Why such dismal fuel mileage??

Are you towing in windy conditions? Are the tires on the trailer at max pressure? Low tire pressure kills mileage. Have you checked your wheel bearings on the trailer to make sure that they are well lubed and rotating freely? Just some thoughts

 

[Silvertip]

Re: Why such dismal fuel mileage??

mthieme -- next time you are towing 7000# at 80 MPH let us know where and when you'll be on the road so we (or at least I) can stay out of your way. No trailer tires are rated for those speeds. As for wind resistance, a boat has LESS wind resistance than most other trailers. Your own mileage claims proves that (9 MPG towing camper and 10 towing the boat). Honda also specs a Ridgeline for more towing weight if you are towing a boat. Box trailers and pontoons are like pulling a barn door through the wind. Also, while I can't dispute your fuel economy claim of nearly 20 MPG towing 7000# at 80 MPH I can consider the calculation a little "suspect".

 

[steelespike]

Re: Why such dismal fuel mileage??

If you have the patience you might try knocking 5 or 10 mph off the speed.
It might surprise you and if your not going to far it won't eat up too much time.Tires can affect mileage,How were the pressures on all the tires.Is the 350 running big bog tires?4:10 gears thats fairly extreme.What is the 350s red line?

 

[muskie hunter]

Re: Why such dismal fuel mileage??

If you have the patience you might try knocking 5 or 10 mph off the speed.
It might surprise you and if your not going to far it won't eat up too much time.Tires can affect mileage,How were the pressures on all the tires.Is the 350 running big bog tires?4:10 gears thats fairly extreme.What is the 350s red line?

The trailer is a 2005, bearings are good and tires were at 65psi as recommended. both trucks are completely stock with the exception of the yukon. I am running a hypertech program on it to improve transmission shifting. 4.10 gears on the ford f-350 are factory. The Yukon redlines at 6000 rpm and just loaps along at 1700 rpm at 60 mph. The ford runs 1800-2000 rpm at 65-70 mph (70 is posted speedlimit in michigan)

 

[Mike722]

Re: Why such dismal fuel mileage??

That is a big differance. One thing I do when checking milage is to make sure you use the same pump, with the vehicle parked in the same direction and close to the same spot.

My Chevy has a long narrow tank and will hold more if the fill end of the tank is at the top of an incline.

 

[mthieme]

Re: Why such dismal fuel mileage??

Calculating mpg isn't rocket science. I didn't believe it at first either, but have used the truck on many occasions. The engine turns 1500 rpm at 80. Owner states he never got that - typically 17 "around town". I'd say she's propped correctly!
BTW, I wasn't towing a boat, although I admit the scenario wasn't much better.
Rt. 81 in WV has a 70 mph speed limit as many do now. If you're not doing at least 70, you'll get run over! Not a justification, but those are the conditions.
You're too far away from me - you're safe!

 

[tashasdaddy]

Re: Why such dismal fuel mileage??

a 1996 wellcraft excel 26 se cruiser is a lot of boat and wind resistance. i'm not surprised.

 

[reelfishin]

Re: Why such dismal fuel mileage??

I used to own a 1997 Ford F350 4x2 Crew cab Dually with the 7.3L, I regularly towed long distance, anywhere from 300 miles to 900 miles. Running with a 28' enclosed box trailer, loaded to about 10,500 lbs. and often towing through the hills and mountains in NE PA, I never saw less than about 11 mpg, and it averaged about 18.5 on most long highway runs, running upwards of the 65 mph limit, often faster. That truck was optioned with only the 3.73 gears and an open rear and E4OD automatic trans. Several buddies all had different versions of the same truck and got similar mileage.
If you are getting that poor mileage on any truck, they either there is a problem with the trailer or tow vehicle or just poor driver habits.

For instance, I and a neighbor have identical cars, I average 26-29 mpg, he gets only 15-18 at best with very much the same types of driving.
I drove his car one weekend, with him along as a passenger, and his car averaged 27mpg, he was amazed at the fact that I could go beyond 400 miles on one tank of gas, he never got to 250 before having to refill the tank. I wouldn't describe his driving as aggressive, or fast, nor mine, but I would say his driving habits are a bit jerky, staying on the gas to the last minute and accelerating faster than needed up to speed. He also has been through two sets of brake pads where as I have not yet worn out the originals.

In your situation, considering that both vehicles have gotten extremely poor mileage while towing the same trailer, I'd look pretty close at that trailer.
Even though it's a heavy load, its still rolling weight. Once at speed on the highway, mileage should improve greatly over stop and go driving.
Also make sure there is a little as possible to catch the wind while underway. Loose covers, bimini tops, either folded or open act as parachutes and can create extreme drag. Anything you can do to make the upper surface of the boat more aerodynamic will do wonders for mileage. This problem increases severely for every few mile per hour, especially at higher speeds. Dropping only a few mph overall can make drastic changes in your fuel usage.

As an example, I added a roll out awning to my enclosed trailer, which on a certain trip had always averaged to get me about 15 mpg over the course of the same trip, with the added roll up canopy, my mileage dropped to only 10.2 mpg, with only the rolled up canopy on the right side of the trailer. I proved it by leaving the canopy home last few times, and my mileage returned to normal on the last two trips.

Proper hitch angle can also affect mileage, as well as wind resistance for obvious reasons.

 

[muskie hunter]

Re: Why such dismal fuel mileage??

I used to own a 1997 Ford F350 4x2 Crew cab Dually with the 7.3L, I regularly towed long distance, anywhere from 300 miles to 900 miles. Running with a 28' enclosed box trailer, loaded to about 10,500 lbs. and often towing through the hills and mountains in NE PA, I never saw less than about 11 mpg, and it averaged about 18.5 on most long highway runs, running upwards of the 65 mph limit, often faster. That truck was optioned with only the 3.73 gears and an open rear and E4OD automatic trans. Several buddies all had different versions of the same truck and got similar mileage.
If you are getting that poor mileage on any truck, they either there is a problem with the trailer or tow vehicle or just poor driver habits.

For instance, I and a neighbor have identical cars, I average 26-29 mpg, he gets only 15-18 at best with very much the same types of driving.
I drove his car one weekend, with him along as a passenger, and his car averaged 27mpg, he was amazed at the fact that I could go beyond 400 miles on one tank of gas, he never got to 250 before having to refill the tank. I wouldn't describe his driving as aggressive, or fast, nor mine, but I would say his driving habits are a bit jerky, staying on the gas to the last minute and accelerating faster than needed up to speed. He also has been through two sets of brake pads where as I have not yet worn out the originals.

In your situation, considering that both vehicles have gotten extremely poor mileage while towing the same trailer, I'd look pretty close at that trailer.
Even though it's a heavy load, its still rolling weight. Once at speed on the highway, mileage should improve greatly over stop and go driving.
Also make sure there is a little as possible to catch the wind while underway. Loose covers, bimini tops, either folded or open act as parachutes and can create extreme drag. Anything you can do to make the upper surface of the boat more aerodynamic will do wonders for mileage. This problem increases severely for every few mile per hour, especially at higher speeds. Dropping only a few mph overall can make drastic changes in your fuel usage.

As an example, I added a roll out awning to my enclosed trailer, which on a certain trip had always averaged to get me about 15 mpg over the course of the same trip, with the added roll up canopy, my mileage dropped to only 10.2 mpg, with only the rolled up canopy on the right side of the trailer. I proved it by leaving the canopy home last few times, and my mileage returned to normal on the last two trips.

Proper hitch angle can also affect mileage, as well as wind resistance for obvious reasons.

Thanks for the help. your fuel mileage is similar to what the owner of the F-350 expected I would have achived. What blows my mind is how a 1997 Gmc Yukon with a fuel injected 350 smallblock running in drive instead of OD gets 8 miles to the gallon. Then on the same trip (different times) a ford f-350 can get 8 miles per gallon. There is absolutely no comparing the 2 trucks. I did however run the F-350 in OD as it was not hunting or working hard whatsoever.

Thanks Steve..

 

[Gary H NC]

Re: Why such dismal fuel mileage??

Any way you look at it you got a pretty hefty boat your hauling. I tow 6000 pounds max with my Tahoe getting the 8mpg...

 

[muskie hunter]

Re: Why such dismal fuel mileage??

Any way you look at it you got a pretty hefty boat your hauling. I tow 6000 pounds max with my Tahoe getting the 8mpg...

Keep talking, your making me feel better about the mpg on the Yukon already!!!
The diesel is another matter though

 

[captharv]

Re: Why such dismal fuel mileage??

The trailer is a 2005, bearings are good and tires were at 65psi as recommended. both trucks are completely stock with the exception of the yukon. I am running a hypertech program on it to improve transmission shifting. 4.10 gears on the ford f-350 are factory. The Yukon redlines at 6000 rpm and just loaps along at 1700 rpm at 60 mph. The ford runs 1800-2000 rpm at 65-70 mph (70 is posted speedlimit in michigan)

1700 RPM at 60? Sounds like you are running in overdrive. WRONG!
Engines have a torque curve, and a HP curve. The HP is derived from the torque X RPM divided by a constant. For purposes of illustration, assume that the 300HP engine rated at 6000 RPM has 150 HP at 3000, 70 at 2000. Lets say that at 60 you need 60 HP. So, at 2000 and 300 you have enough? No.
At 2000 there is only 10 HP in reserve. The engine is straining. Creating a lot of internal heat. At 3000 you have 90 HP reserve. Thats why they recommend towing with O/D disabled.
I have an Expedition 4X4 with the factory H/D tow package (3.73:1, limited slip), and a 5.7 L. I tow with O/D off, and get 2400 RPM at 60. we took a long trip with mostly turnpike driving last July, and I bragged about 9.0 MPG. I am towing about 7800# on a dual axle trailer with radial tires. If I use O/D the vehicle computer said about 7 MPG and was straining.
This is not one of those my-truck-is-better-than-yours post, but giving real world data. Hey, how many ways can you make an engine.....
Retest with the O/D disabled. You may find the MPG gets better.
Another thing: The tranny. Its cooled thru the radiator and the external cooler. The fluid is pumped thru by the internal pump in the tranny. Insufficient cooling (and subsequent damage) occurs when the fluid is being pumped slower (low RPM) and it doesnt cool enough. This is not to mention the burning of the internal clutches (16 or so) because the pressure from the pump holds them together. Low pressure=slippage
My buddy's son has a dually diesel 350. he hauls multiple cars in an enclosed trailer. He burned two trannys in O/D. The Ford people told him to disable O/D. No more problems.
Hey, just trying to help.

 

[TerryMSU]

Re: Why such dismal fuel mileage??

The trailer is a 2005, bearings are good and tires were at 65psi as recommended. both trucks are completely stock with the exception of the yukon. I am running a hypertech program on it to improve transmission shifting. 4.10 gears on the ford f-350 are factory. The Yukon redlines at 6000 rpm and just loaps along at 1700 rpm at 60 mph. The ford runs 1800-2000 rpm at 65-70 mph (70 is posted speedlimit in michigan)

WRONG! 70 is passenger vehicle only. With trailer it is only 55. See sticky at top of this forum. It confirms that limit for trailer is 55. I believe that info is also posted on the on-ramp to the highway as well (if I remember correctly).

TerryMSU

 

[muskie hunter]

Re: Why such dismal fuel mileage??

1700 RPM at 60? Sounds like you are running in overdrive. WRONG!
Engines have a torque curve, and a HP curve. The HP is derived from the torque X RPM divided by a constant. For purposes of illustration, assume that the 300HP engine rated at 6000 RPM has 150 HP at 3000, 70 at 2000. Lets say that at 60 you need 60 HP. So, at 2000 and 300 you have enough? No.
At 2000 there is only 10 HP in reserve. The engine is straining. Creating a lot of internal heat. At 3000 you have 90 HP reserve. Thats why they recommend towing with O/D disabled.
I have an Expedition 4X4 with the factory H/D tow package (3.73:1, limited slip), and a 5.7 L. I tow with O/D off, and get 2400 RPM at 60. we took a long trip with mostly turnpike driving last July, and I bragged about 9.0 MPG. I am towing about 7800# on a dual axle trailer with radial tires. If I use O/D the vehicle computer said about 7 MPG and was straining.
This is not one of those my-truck-is-better-than-yours post, but giving real world data. Hey, how many ways can you make an engine.....
Retest with the O/D disabled. You may find the MPG gets better.
Another thing: The tranny. Its cooled thru the radiator and the external cooler. The fluid is pumped thru by the internal pump in the tranny. Insufficient cooling (and subsequent damage) occurs when the fluid is being pumped slower (low RPM) and it doesnt cool enough. This is not to mention the burning of the internal clutches (16 or so) because the pressure from the pump holds them together. Low pressure=slippage
My buddy's son has a dually diesel 350. he hauls multiple cars in an enclosed trailer. He burned two trannys in O/D. The Ford people told him to disable O/D. No more problems.
Hey, just trying to help.

Woops my bad!! what I meant to say was without the boat and at 60mph the Yukon turns 1800rpm. I always pull the boat with OD off. The 4l60e transmission will not handle it in overdrive. I pulled the boat with the f-350 in OD because in tow haul mode the rpms were almost at 3000. The 7 liter diesel redlines at 3500 rpm.

 

[crb478]

Re: Why such dismal fuel mileage??

"The truck was run at 65-70 mph and the tach was showing 1800-2000 rpm."

My F250 7.3 diesel with 3.73 gears is turning about 2000 rpm at 65 mph with stock tires, which is the top of its sweet spot for milage. I would think that a F350 which weighs more would be turning closer to 2400 rpm with 4.10 gears at 70 unless he has something like a gear venders overdrive added. If the F350 has oversized tires the rpm's will drop some at speed, but it will loose milage getting up to speed. Diesels like to run at lower rpm's, and 1800 on a 7.3 is about optimum. Above that and you will pay the price. I would have thought that it would have got 12 to 14 mpg if it was consistently run near 1800 rpm.

 

[muskie hunter]

Re: Why such dismal fuel mileage??

"The truck was run at 65-70 mph and the tach was showing 1800-2000 rpm."

My F250 7.3 diesel with 3.73 gears is turning about 2000 rpm at 65 mph with stock tires, which is the top of its sweet spot for milage. I would think that a F350 which weighs more would be turning closer to 2400 rpm with 4.10 gears at 70 unless he has something like a gear venders overdrive added. If the F350 has oversized tires the rpm's will drop some at speed, but it will loose milage getting up to speed. Diesels like to run at lower rpm's, and 1800 on a 7.3 is about optimum. Above that and you will pay the price. I would have thought that it would have got 12 to 14 mpg if it was consistently run near 1800 rpm.

Yep!! 1800-2000 65-70 mph on flat ground all highway all stock truck! Or atleast get better than the Gmc Yukon!!!

 

[45Auto]

Re: Why such dismal fuel mileage??

You'll find in the real world that lots of those high gas mileage numbers for towing are "estimates" by the owners. Don't be surprised if you really check it and they're substantially lower, as you've seen!