How to drive with big power for MPG's

about as good as it's going to get till summer.

I had my DD S60 14L tuned by rebel127. I was upper 6's last summer and have since dropped about 1 mph to upper 5's, lower 6's. I am running around 550 hp and 2060 torque.

If I am empty and such, I can see 8.3 MPG on the dash.

Light loads where I have decent 35+ temps, I can see 7+.

As soon as I see the ambient temps hit under 30 *F, the mileage drops off.

I have a 07 Century, 13 spd and 3.42 rears. I was seeing 6.4 mpg with no wind going out to Henderson CO with 40K in the box across I80. I was running it at 1500 RPM just like was suggested. If I ran it at 1375, I was around 5.8, 1450, I was around 6.1 mpg.

 

Try pulling out the fleet air filter and going back to the stock one. When I put the fleet air in my 780/D12 the mpg tanked. Went back to stock and mpg went up. Iowa 80 refunded my $299. Trying running at higher rpm, 1500 ish. Just like the above experience, I had a 41k load from Dallas to Vegas and got 6.7 average running at 1510 rpm. If I ran at 1350 with that weight my mpg dropped to 5.9. I really think these D12s like to be run at the high end rpm.

 

It's the winter blend fuel. This time of the year, most places are required to mix the diesel for non gelling. Which cause everyone to get 1-1.5 mpg less.
Try getting fuel down south and avoid as much as one can up north. The further south, the less winter blend. I heard it's 5 grades of winter blend depending on the time of year and average climate for the area.
Also can add centan boost fuel additive which helps, but not sure if it helps enough to make the difference of the cost of the additive.

During the summer months I get over 7.5. This last month I got 6.6

I'd really like to know, is it really needed for the oil companies to make winter blend diesel?

 

I try to cruise with the boost as far below 15 as possible to get the best mileage. At 15 or so and above you will not be able to get what I consider to be decent(7 mpg+) fuel mileage. These engines are supposed to have a sweet spot when it comes to rpm's. Under ideal conditions they may. But what matters far more most of the time is how hard the engine has to work to maintain your desired speed/rpm. Sometimes dropping/splitting a gear will do the trick when the engine is lugging a little. A lot of times when cruising it just won't matter much. The boost gauge will provide you with that information.

Other posters have mentioned winter blend fuel being an issue. Another is the wind. This winter has had a fair amount of lousy weather which usually includes more wind. That's what causes my fuel mileage to suffer more than anything else. And I think its worse when your loaded light as I generally am.

Climbing steeper grades like on I80 in PA I don't try to keep the boost below any certain level. It takes power(i.e. fuel) no matter what, so the quicker you get to the top, the better, is how I look at it.

 

Normally if I have a light load, say 20k or less, I will run at 1350 rpm which is 57 mph with my set up. This will give me 7+ and at times I've got into the 8s. However, with anything 35k and above in the box the 1350 rpm does not work. The engine is just laboring too much and boost is high all the time. If I drop a gear, 12 to 11 which is direct on my tranny, the road speed drops way too much and is frankly dangerous. So I must increase the rpm to 1500 to stop the turbo boosting as much. My road speed will increase to 64 mph but my mpg is better than what i would be getting at 57 mph. This is the reason why I avoid loads more than 25k. I run for Landstar so I am fortunate that I can pick and choose my freight and keep the weight down. My last load was a show load and I just got unlucky with the weight. If I had known it was a 41k load I would have passed on it. Show loads are normally 20k or below.

 

just floor the pedal and skip as many gears as possible when getting up to speed, then cruise at lowest possible rpm, you want to use the extra torque the box gives. At level ground and steady cruising those boxes do not help at all.

 

Thanks for sharing this info.

 

Ive never paid attention what air filter I had in my truck but once got new Fleet filter from the dealer
upon changing it my truck got slower with response to the gas pedal and overall acceleration.. it was way back on my Volvo with N14 engine
so I checked what air filter I had and simply bought another one..
Since then I use only Donaldson air filters