What mods to maximize MPG

[RMarkey]

The speed limit part wouldn't be a problem but we're getting to many people with what I call "The California Surge. " For some reason the californians, and a lot of other people now, have that whole speed up past the speed limit, then let off and let it slow down below the speed limit, the repeat process untill arriving at destination, or unitll I need to pass, then they'll speed up! That drives me crazy to no end, especially because I'll try to use the cruise control sometimes, and it makes it impossible. That's gotta hurt mpg I would think.

 

[JoelMartin]

The speed limit part wouldn't be a problem but we're getting to many people with what I call "The California Surge. " For some reason the californians, and a lot of other people now, have that whole speed up past the speed limit, then let off and let it slow down below the speed limit, the repeat process untill arriving at destination, or unitll I need to pass, then they'll speed up! That drives me crazy to no end, especially because I'll try to use the cruise control sometimes, and it makes it impossible. That's gotta hurt mpg I would think.

I know exactly what you mean. Around here they gain speed down hill and then lose speed uphill. That is so maddening when trying to use the cruise.

 

[ohnoitsyu]

I know exactly what you mean. Around here they gain speed down hill and then lose speed uphill. That is so maddening when trying to use the cruise.

Be careful with that cruise control. We take advantage of the downhills and go fast to gain momentum, then ease up on the throttle on the uphills. :-laf

 

[BHolm]

I think the simple fact is, the truck we are talking about is far from broken in. Once you get it there the milage will come was up. My 06 mega started out getting 13. 5, by 30k miles it was getting 20. There was a lot of heavy towing in there too. Not driving it because the milage stinks, or trying to drive it around like grandma isn't going to solve the problem. That truck needs some hard and heavy work, a bunch of it, before the milage is going to come up. No mod out there is going to change that. Good Luck

 

[AKaiser]

I know exactly what you mean. Around here they gain speed down hill and then lose speed uphill. That is so maddening when trying to use the cruise.

That's actually better for fuel economy. Most OTR trucks are set up to do that intentionally for that very purpose.

 

[JoelMartin]

That's actually better for fuel economy. Most OTR trucks are set up to do that intentionally for that very purpose.

I guess that could be true but I like to just set my cruise and go. Besides the majority of the people are not trying to get good fuel mileage and they're just holding up traffic.

 

[betterthanstock]

Be careful with that cruise control. We take advantage of the downhills and go fast to gain momentum, then ease up on the throttle on the uphills. :-laf

That's actually better for fuel economy. Most OTR trucks are set up to do that intentionally for that very purpose.

That is a fallacy that comes from weak hybrid engines that cannot sustain power output over a long hill. Most internal combustion engines have highest efficiency at WOT (or just a little less, because of what the fuel mixture does at WOT with most oxygen sensors), as long as you have a manual transmission, or it stays in top gear and locked up with an auto. Best efficiency is at the lowest RPM that you can pull the hill.



By keeping speed constant, you get better fuel mileage, than varying it up and down, as long as you do not use the brakes (or engine braking) downhill, and no downshifting up hill. This varies wildly for most cars, depending on specific power.



So, in general, weak engined cars get better mileage by speeding/slowing. Powerful engines get best mileage at steady speed on cruise.

 

[AKaiser]

That is a fallacy that comes from weak hybrid engines that cannot sustain power output over a long hill. Most internal combustion engines have highest efficiency at WOT (or just a little less, because of what the fuel mixture does at WOT with most oxygen sensors), as long as you have a manual transmission, or it stays in top gear and locked up with an auto. Best efficiency is at the lowest RPM that you can pull the hill.



By keeping speed constant, you get better fuel mileage, than varying it up and down, as long as you do not use the brakes (or engine braking) downhill, and no downshifting up hill. This varies wildly for most cars, depending on specific power.



So, in general, weak engined cars get better mileage by speeding/slowing. Powerful engines get best mileage at steady speed on cruise.

Au contraire. It has nothing to do with hybrids. Fact is, if you are going up a hill, that puts the engine under load. Depending on how steep the hill, therefore how much load, the ECM is going to give 'er the fuel to keep up the speed on the way up. It will do the exact opposite on the way down, so the fuel use may very well balance out, but it will increase fuel on the upslope. It may be that it's a small factor unloaded, but under loads, it definitely is a factor.



The reason semi-tractors come with programable "droop" as they call it is to allow the truck to burn less fuel on the uphill climb without disengaging the cruise control. They also work the other way on the downslope, allowing the truck to build momentum for the next hill without burning more fuel.



BTW, these engines DO NOT get the best FE at WOT. They get it around 15-1600 RPM, which is the lowest HP point on the maximum torque lb-ft of the engine, 5. 9 L anyway.

 

[ColoradoKing]

The desire to get the best possible mileage is commendable. As has been well covered above, best possible mileage requires proper break-in, can be enhanced with certain cheap and/or expensive power options, and by avoiding erratic or over zealous use of the right foot. What hasn't been covered is the pitfalls of being too gentle on the accelerator.



In order to sustain a clean running, fuel-efficient engine (clean injectors, de-carboned valves/pistons), the occasional hard acceleration or loaded engine is mandatory IMO. I drive conservatively for 98% of each tankfull, then I look for a big hill (or Chevy, or Ford) - and drop the throttle long enough to blow clean. Sometimes it takes a few times.



After running diesels for years on the water, during teardown you could see the difference between a continuously loaded engine and a "babied" one, where the engines were otherwise identical. In a remarkably short time, carbon build-up on an under-loaded diesel is brutal, and can cause catastrophic failures from cylinder or bearing scoring, oil breakdown, or valve dropping from carbon chunks. I bought my '05 used, and it had two engine replacements before it hit 50K. The only mention on the work ticket was "noise coming from engine - replace engine and injectors". High EGTs are a fact of life on a working diesel, but as long as they're just high, and not over-temp, you're burning fuel efficiently and keeping the engine clean.



I add a half gallon of Seafoam to a half tank every so often, and it cleans the fuel system out nicely. If you follow the above, you'll not only get better fuel economy, you'll get more miles, too.

 

[RMarkey]

At least they speed up on the down hill. In my work truck(Kenworth) That works fine for me. Around here they slow down and ride the brakes down the hill, then hit the uphill and take off, about the worst possible thing for mpg I think. It also sucks with a load on because it takes about everything I've got to get moving up the hill after braking down the last hill. I like to coast, can't beat the mpg then!

 

[ColoradoKing]

No kidding. Drives me crazy when people have no clue. Happiness is a downhill and uphill, with no one in front and no cops... .

 

[geusterman]

My 04. 5 was 12 ish at 10K... I was disheartened after my 02 6spd but at 20K and easy throttle on freeway I came back 80 miles later to the same pump and topped off again... 17. 8. No mods except gauges. Might try EZ or something later. George

 

[captainmike]

All this sounds great. BUT, the number #1 MPG saver is your right foot. Drive like there is an eggshell under it, accelerate slowly, get off the pedal early when you see a red light ahead, and keep it under 65 mph. Otherwise have fun with all the diesel power, and don't complain about the mileage.

Cheers, Mike in Florida

 

[WStrmiska]

The Cummins is made to work not be babied, the harder you work it the better milage you will get. If you ever get a chance, talk to any of the guys that have over a million miles on thier truck. I think thier is a 1,000,000 mile club. Some one will chime in on this I'm sure.

 

[Bachant]

Hard driving will result in poor milage. I have just over 154,000 on my 06 so I have driven a couple miles to test my responce. Driving slow doesn't mean you'll get 20+mpg but it will help youe milage woes. My best so far is 20. 5mpg. Not all trucks will get the same milage.