Chevy/GMC Duramax

[newroswell]

Holding out for the 2012 might be a good idea. After taking an MPG beating the last few years when the tough emissions hit, MPG is going in the right direction on all 3 diesels. Not where it was, but they're all putting out even bigger HP/Torq. You'll love the diesel. Now if I could just train my gas buddies to stop taking the one diesel pump when we pull in for fuel when the gas only pumps are open.

[BillTex]

Originally Posted by moosetags

To answer your question about expected fuel mileage, I really don't have any idea. I have never owned a diesel, so I am new at this. I would have probably stuck with gas for just towing Lucy. I will be toting about 2500# of truck camper and towing a 7400# Airstream. We have decided that we are going to need diesel is we want this rig to be able to go uphill. It will be interesting to see how this will work out fuel mileage-wise.

Maybe some with diesel experience can chime in with what they think on MPG.

Brian

Expect 15-16 loaded up.
22-24 cruising down the highway with no load...
Even loaded up...you will have 500+ mile range.

Bill

[moosetags]

Originally Posted by BillTex

Expect 15-16 loaded up.
22-24 cruising down the highway with no load...
Even loaded up...you will have 500+ mile range.

Bill

I assume the 15/16 is with just the TC. By the way what does your TC weigh-out at ready to go camping? What do you get pulling the AS?

Brian

[BillTex]

Originally Posted by moosetags

I assume the 15/16 is with just the TC. By the way what does your TC weigh-out at ready to go camping? What do you get pulling the AS?

Brian

I am now getting 16 mpg towing the AS fully loaded over 7000#-7500#.
15 mpg hauling the TC fully loaded 2700#-3000#.

I attribute the difference to aerodynamics.

I suspect, with the lower profile of a pup-TC you will be getting about same, regardless of total weight. The diesel will shrug off much of the weight. Can't deny the aerodynamics.
You will find the best way to drive a deezul is much like riding the Harley...roll on the throttle nice and easy..don't stomp on it...you will make better use of the power, and increased efficiency.You don't need to go looking for the torque at the upper end of the rev band. It'll be there...all the time.

There is no doubt that 400hp and 700 lb/ft will throw you back in the seat...but you won't want to drive that way...
With the diesel, you drive by RPM to seek peak power (1800 RPM) and peak efficiency (1800 +/- 100 RPM).It's not like a gasser where you have to rev the hell out of 'em to get the load moving, or keep it moving.
You'll be able to move that load at idle. And you'll likely never experience a down shift on the road. Use the TH mode whenever you load up; makes life easy and gives you the engine braking of the Alli. I use it TC or AS.

Bill

[NevadaGeo]

Add 4 cents per gallon of fuel for the antigel additive, that could be important in the outback at below Zero. I haven't seen a pump that advertises it as being already in the fuel.

[moosetags]

Originally Posted by BillTex

I am now getting 16 mpg towing the AS fully loaded over 7000#-7500#.
15 mpg hauling the TC fully loaded 2700#-3000#.

I attribute the difference to aerodynamics.

I suspect, with the lower profile of a pup-TC you will be getting about same, regardless of total weight. The diesel will shrug off much of the weight. Can't deny the aerodynamics.
You will find the best way to drive a deezul is much like riding the Harley...roll on the throttle nice and easy..don't stomp on it...you will make better use of the power, and increased efficiency.You don't need to go looking for the torque at the upper end of the rev band. It'll be there...all the time.

There is no doubt that 400hp and 700 lb/ft will throw you back in the seat...but you won't want to drive that way...
With the diesel, you drive by RPM to seek peak power (1800 RPM) and peak efficiency (1800 +/- 100 RPM).It's not like a gasser where you have to rev the hell out of 'em to get the load moving, or keep it moving.
You'll be able to move that load at idle. And you'll likely never experience a down shift on the road. Use the TH mode whenever you load up; makes life easy and gives you the engine braking of the Alli. I use it TC or AS.

Bill

Thanx for the info, Bill. It sounds like this diesel thing is going to be a gas (no pun intended). I understand the Harley thing. As a young man, I was a motor officer with the Tallahassee Police Department. I spent three years riding a Harley full time. I'm afraid that I was not very light on the bike's throttle in those days. I rode a hand shifter (foot clutch) Harley for all it was worth. I will try to be easier on the Duramax.

Brian

[BillTex]

Originally Posted by moosetags

Thanx for the info, Bill. It sounds like this diesel thing is going to be a gas (no pun intended). I understand the Harley thing. As a young man, I was a motor officer with the Tallahassee Police Department. I spent three years riding a Harley full time. I'm afraid that I was not very light on the bike's throttle in those days. I rode a hand shifter (foot clutch) Harley for all it was worth. I will try to be easier on the Duramax.

Brian

Heel/toe is the only way to ride!
My point is; diesel develops power quite a bit different than a gasser...it's a more relaxed way of driving...you'll see; a light touch on the throttle with your big toe...and your off and moving. No screamin' high RPM assaults on inclines, no downshifting...just relax and let it roll.

As far as the comment above on additives; when in cold climates, there is winter blend in the pump. Common rail injection=no need for additives. We routinely use our truck in ski country...have been as cold as -30 deg F...no issues...starts right up, no different than gas.
This is our first deezul, and I had some of those concerns that you hear thrown around on the web by those who never owned deezul (cold weather, can't find fuel, yada...) I can only say our experience has been very positive, I can't see ever going back to gas...it's that good...and all those base-less commments...well...base-less. May have been true years ago, don't know (this is our first deezul as mentioned), not true any more.

I am excited for you and your new adventure...you will have quite the set-up!

Bill

[SteveH]

It's spelled Diesel because it was invented by a man named Rudolf Diesel.

Rudolf Diesel was born in Paris in 1858. His parents were Bavarian immigrants. Rudolf Diesel was educated at Munich Polytechnic. After graduation he was employed as a refrigerator engineer. However, he true love lay in engine design. Rudolf Diesel designed many heat engines, including a solar-powered air engine. In 1893, he published a paper describing an engine with combustion within a cylinder, the internal combustion engine. In 1894, he filed for a patent for his new invention, dubbed the diesel engine. Rudolf Diesel was almost killed by his engine when it exploded. However, his engine was the first that proved that fuel could be ignited without a spark. He operated his first successful engine in 1897.
In 1898, Rudolf Diesel was granted patent #608,845 for an "internal combustion engine" the Diesel engine.

[BillTex]

Originally Posted by SteveH

It's spelled Diesel because it was invented by a man named Rudolf Diesel.

Rudolf Diesel was born in Paris in 1858. His parents were Bavarian immigrants. Rudolf Diesel was educated at Munich Polytechnic. After graduation he was employed as a refrigerator engineer. However, he true love lay in engine design. Rudolf Diesel designed many heat engines, including a solar-powered air engine. In 1893, he published a paper describing an engine with combustion within a cylinder, the internal combustion engine. In 1894, he filed for a patent for his new invention, dubbed the diesel engine. Rudolf Diesel was almost killed by his engine when it exploded. However, his engine was the first that proved that fuel could be ignited without a spark. He operated his first successful engine in 1897.
In 1898, Rudolf Diesel was granted patent #608,845 for an "internal combustion engine" the Diesel engine.

Deezul= play on words

kewl?

and yes, we all know Rudy ran the first DIESEL on p-nut oil!

[SteveH]

Originally Posted by BillTex

Deezul= play on words

kewl?

and yes, we all know Rudy ran the first DIESEL on p-nut oil!

Yes, it's cool, and I didn't doubt that most, if not everyone knew.

It just sort of bothers me because I find it a bit disrespectful. I know what it's like having a difficult (in this country) and unusual last name, and having delt with all the misspelling, and intentional mispronounciations all my life.

I know it may be just me, but I believe we owe a great inventor at least the correct spelling of his name, especially such an easy one.

Additionally, it seems that a lot of people, some more than others, take pride in misspelling lots of words on the net, and think that's cool, or the "in thing", and maybe I am a prude, because I don't think so. I don't profess to be a great speller, or even good in grammar, but I think we should at least try. YMMV.

OK, off the podium.

[moosetags]

To take the Rudolf Diesel story one step further, he mysteriously disappeared while a passenger aboard the Mail Steamer Dresden in route from Antwerp to England on September 13, 1913. Two weeks later a decomposed body body was found by a freighter in the English Channel. Possessions recovered from the body were later identified by Rudolph Diesel's son as belonging to his father. Whether Rudolph Diesel's death was accidental or possibly murder is unknown to this day. Homicide was never ruled out as Diesel was involved in significant patent disputes at the time of his death.

Brian

[moosetags]

If I can get 15 mpg on the new Duramax, I will be very pleased. That would be a 50 percent increase. That would cover the higher per gallon price, and start eating up the cost of the Diesel option.

Brian

[BillTex]

Originally Posted by moosetags

If I can get 15 mpg on the new Duramax, I will be very pleased. That would be a 50 percent increase. That would cover the higher per gallon price, and start eating up the cost of the Diesel option.

Brian

Towing and unladed highway driving are where the deezul really has an advantage with economy.
Around town, expect the same as a gasser.
Ours is used for adventures...and not much around town (I bike to the office) so it is usualy loaded up and headed for the open road...much as you will be using your truck.

I suspect you will really like the diesel...and your load will justify it!

Bill

[moosetags]

I am really looking forward to the Diesel experience. I have started pricing the truck. One dealer in Jacksonville would only go 4 percent off of MSRP. Another dealer in the Panhandle told me that I could choose from what they had in stock (no 3500's at all) or wait until they got more stock in. The salesman at this dealership told me that they had a Silverado 1500 in Victory Red in stock and that I should jump on that since it was the right color. I can't believe that people that stupid are allowed out by themselves.

Brian

[noreen&sal]

Originally Posted by moosetags

I am really looking forward to the Diesel experience. I have started pricing the truck. One dealer in Jacksonville would only go 4 percent off of MSRP. Another dealer in the Panhandle told me that I could choose from what they had in stock (no 3500's at all) or wait until they got more stock in. The salesman at this dealership told me that they had a Silverado 1500 in Victory Red in stock and that I should jump on that since it was the right color. I can't believe that people that stupid are allowed out by themselves.

Brian

Just a normal car salesman. Sal.

[txhippiefish]

I've really enjoyed this thread. I share the common happiness with the Duramax & Allison combo. But, I've also had a very different experience with my truck. She's a 2009 2500HD LTZ 4x4 (LMM Duramax) bought brand new at the end of Oct 2009. I couldn't resist naming her "Allison". Since new, I've put over 53,000 miles on her. Obviously low miles for a diesel, but not too shabby for only 17 months. I absolutely love everything about it...until I customized it!

Customizations:
- Ranch Hand bumper replacements both front & back.
- NFAB 6-step access steps (three per side)
- DeeZee bed rail caps on all four rails
- all the above parts were black from the factory. I had a shop paint match and powder coat to match the Chevy factory white of my truck
- BD Suspension Lift (7" front & 5" rear with add-a-spring not a lift block in rear)
- XD Addict 18" wheels & ~35" BFG All-Terrains
- HyperTech tuner to adjust tire size and use Stage 1 performance tune full time.

The truck looks great. I'm very pleased with the ride and performance of the lift kit. The tires are great and road noise is nothing to complain about. I don't notice the additional performance of the tuner unless I stand on the throttle (which very rarely occurs).

Here's where things start suckin' for me! The larger diameter tires have totally screwed my gearing. I tow a 2011 34' Classic (her name is Abigail). I'm a full timer, so Abigail is always heavily loaded. I weighed the rig on a CAT Cert Scale last week on a trip...17,400lbs with no driver or passengers but full diesel and fresh water tank.

Always use tow/haul with AS connected. Tranny will never go into 6th gear. It will stay in 5th and often downshift to 4th with only a slight hill. Worse yet, it often will go back to 5th before cresting the hill only to downshift to 4th again and dump fuel chasing the cruise control speed. On this last trip, I found the best "experience" was achieved by using manual mode, locking the tranny in 4th gear and settling for 67mph at just shy of 2500 RPMs. On a longer downhill, I'd click manual up to 5th to coast more but that really didn't seem to increase fuel efficiency or reduce tranny temp. The tranny consistently ran 100-120 degrees hotter than whatever the ambient temp (ie. 10 degrees outside & tranny would be ~110 degrees. 80 degrees outside & tranny would ~200 degrees. Engine temp never indicated a noticeable change on stock dash temp gauge. MPG averaged 9-11 depending on the terrain. Without towing, I get 14 around town and 16/17 on the highway if I stay close to 70.

This thread has referenced 1800 RPMs as peak efficiency for the Duramax. I can't keep it around 1800 for my life. It will downshift as soon as it tries to maintain the speed.

Thoughts? Ideas? Concerns? I'm very interested to hear what y'all have to say.

PS...sorry for such a long read!

[DKB_SATX]

Originally Posted by txhippiefish

~~~
Thoughts? Ideas? Concerns? I'm very interested to hear what y'all have to say.

PS...sorry for such a long read!

Go back to the original tire size?

You don't offer a detailed description of how it performed under load originally, but it seems like you were happy with the performance, and then it became a point of concern when you changed the wheels and tires.

[slowmover]

Re-gear to match factory spec (or more likely, numerically higher than that to offset increased pressure drag and rolling resistance). Better, lose the lift and the offroad tires, IMO. The cost of looking cool isn't worth it: higher operating cost per mile and shortened life span. Offroad tires are poor (to be generous) for highway towing; in a number of important ways (a separate subject to be searched).

Take the specific question (cruise rpm) to one of the D-Max boards and see what others have done plus what their advice may be. You want the specific dyno graph and BSFC numbers of your engine spec to use a gear calculator. To tailor shift points the engine must run each gear within a particular rpm range. Once it is outside of this it can be some real work to re-create.

There may already be a table of this -- transmission rpm range and shift points under several scenarios (light, heavy, WOT) -- which others can link you to. A diesel, even a wannabe like the D-Max, has a smaller rpm range than a gasoline engine. We can't just rev them once we put in a hotter cam (as with gas) and push the shift points higher to compensate (as one example).

Find the tire manufacturer tire height (published) and measure the tires as well. Take your time. Small measurements being off can accumulate and create less than desirable results. The difference, say, between 4.11 gears and 4.33 may be huge in perceived performance, yet small in mpg.

Here's a set of calculators to play with. Also, scale the truck (as you already should have) set up for extended travel (heaviest likely weight) with per axle numbers.

It is one thing to alter a truck, it is quite another to re-create the overall quality of the stock truck (as you've learned).

On mine the highest BSFC numbers come just under 2000-rpm (most work for least fuel), but the road speed is too high to use that when solo once the effects of pressure drag (aerodynamic resistance) is calculated. The small change in rpm reduction to travel at 60 mph (1,750 rpm) is accompanied by a huge reduction in fuel burn, so even a less than "perfect" cruise rpm works to main advantage. 15% higher fuel burn or 5% less than perfect rpm? The dyno numbers must be "translated" into real life conditions.

To extend this, the range of 1,700 to 2,100 rpm is where the most efficient cruise rpm for all conditions will exist on a CTD of my vintage. The transmission shift points must work with this in order to "stair step" their way up as we accelerate. Peak torque and peak horsepower must be accommodated by trans gearing and torque convertor rpm design in an automatic. If OD is unusable then it seems obvious that the shift out of the powerband needs correction.

It's nice looking and a cool trailer, but either return to stock or continue with the $3k+ gearing changes, and possible custom TQ converter at above $1k. I would expect another $1k on top of that to round things off. Call it $5k at the outside.

In the diesel world it is always tempting to add a magic box to "fix" things. I disagree. It's fundamental abuse as no magic box comes without a cost to offset it's promised advantage. Do the mechanical relationships first, test, and then maybe a software tweak. Maybe.

Good luck

.

[dscluchfc]

The larger the tire size in the rear, the more torque required to push the weight forward.
The smaller the tire size, the less torque required to push the load forward.

I experienced this with the old Yukon I had with the 265 x 75 x 16 tires vs the 245's that other people had who were towing similar loads. The bigger tire size killed me....it looked cool, but it wasn't worth a darn for performance.

[txhippiefish]

Originally Posted by DKB_SATX

Go back to the original tire size?

You don't offer a detailed description of how it performed under load originally, but it seems like you were happy with the performance, and then it became a point of concern when you changed the wheels and tires.

The performance was what you'd expect from the stock Duramax limited by the required emissions controls. The MPGs were better than a gasser, but not that of older, less restricted diesels. Plenty of torque and great tow capability!

It still has plenty of power to tow my AS and 27' boat...just costs more to do so since the "effective gearing" isn't "tuned" anymore to stay in the small sweet spot.

The ride is arguably the same or better than stock with the BD lift. Very happy with the lift product!

Be nice to have unlimited funds and have two trucks...one to tow with and one for ground clearance operations.