Performance Issues 2005 2500HD

[Alan K]

I own a 2005 2500HD 4x4 6.6 Duramax, getting 16 to 17 MPG running light, 9 MPG pulling 12K load. Speed avg 70 MPH. Previously owned 2001 2500HD it got 20-21 MPG light and 12 MPG pulling same load. Question, is the difference due to changes to the engine in 2005 or do I have a problem with the newer truck?

[Robyn]

First off
Welcome to TDP glad to have you aboard :D :D :D

From what I see in the new rigs the power is good but the mileage numbers seem to be all over the sky.
Go to the Dmax forum here at TDP and ask this question of the Dmax owners and se what you get.
Im betting your right in the sweet spot.
I own 6.5's and they have their little nitch too.
16-20 on the 6.5 light and 12 to 14 pulling depending.

Towing takes power and the horse likes to eat if its going to work hard.

See what others say at the Dmax forum

good luck :)

Robyn

[rob from bc canada]

It seems 05's drop off in mileage very quickly with speed, especially of course if your load is not very aerodynamic.

Furthermore, with the extra power, you don't realize how much wind you're pushing. Try running 60-65, it will improve it quite a lot.

That said, your 9 mpg seems excessively low. Make sure you've got a clean air filter, and maybe chnage the fuel filter too. If that doesn't help, try and clean your MAF sensor, and run some injector cleaner through the fuel.

[Mark Rinker]

I have owned an '05 and an '01. Currently own an '02, '04, and '06. I sold the '05 with only 78K on it, partly because the mileage was so low compared to the older LB7s. Since then I have bought the '04 and '06.

Your mileage findings are nearly identical to mine. I attribute it (the low '05 numbers) to the addition of EGR and catalytic converter systems, and the variable-vane turbo compared to the wastegated LB7s.

My favorite trucks are the early LB7s. I just bought the '06 (because it was priced right) and don't have any data on it yet, but my expecations are low - mileagewise.

[iljusin]

I own an '05. Your mileage findings are nearly identical to mine. I attribute it to the higher power and not os efficient engine.

[Buck]

My '05 Dmax used to get those mpg numbers also...then I got some upgrades from John Kennedy and now my '05 is better than my old '01 Dmax ever was. :D ;)

[Mark Rinker]

Good to know that JK's custom tunes can find mileage on the LLY's as well. How much towing vs daily driving do you do? Can you give us some figures?

[Alan K]

My '05 Dmax used to get those mpg numbers also...then I got some upgrades from John Kennedy and now my '05 is better than my old '01 Dmax ever was. :D ;)

You mentioned John Kennedy upgrades.I am not familier with this source. Where I can I find info?

[Alan K]

Good to know that JK's custom tunes can find mileage on the LLY's as well. How much towing vs daily driving do you do? Can you give us some figures?

Towing is probably 80% of my driving.

[Alan K]

My '05 Dmax used to get those mpg numbers also...then I got some upgrades from John Kennedy and now my '05 is better than my old '01 Dmax ever was. :D ;)

Ok I have looked at all the upgrades available from John Kennedy and would like to pursue them. I am not comfortable installing some of these myself. I live in northern New Mexico, any info out there on a shop that could do this work?

[Mark Rinker]

Any diesel performance shop, or even a good general repair shop versed with Duramax diesels under the hood.

[killerbee]

Towing is probably 80% of my driving.


the best economy improvements, will be the ones that keep your fan off.

Get an effective CAI (do research to find one that actually works) to lower your IAT. This is the main problem. IAT goes off the chart when the fan starts up, which in turn leads to more fan.

[Kennedy]

Ok I have looked at all the upgrades available from John Kennedy and would like to pursue them. I am not comfortable installing some of these myself. I live in northern New Mexico, any info out there on a shop that could do this work?


Most of my stuff is DIY and there are many reviews/install tips found on this site.

[Alan K]

the best economy improvements, will be the ones that keep your fan off.

Get an effective CAI (do research to find one that actually works) to lower your IAT. This is the main problem. IAT goes off the chart when the fan starts up, which in turn leads to more fan.

Sorry but I do not know the acronyms....... CAI and IAT??

[killerbee]

Cold Air Intake
Inlet Air Temperature (airbox temp)

IAT is extremely essential to keeping the fan off because if it is allowed to rise, then the charge air cooler can produce more heat than the radiator, and keep the fan on ad infinitum. Not to mention power reduction. Economy suffers so much because of reduced power and the parasitic fan losses, these will total over 70 HP lost on a grade. But you are still burning the same amount of fuel while going slower. miles per gallon

[Mark Rinker]

Killerbee - In this case, I think a good question, before hinting at a solution would be:

"Does your fan clutch run excessively while towing - episodes where the fan will run and run, but high temps don't subside?"

From my understanding, a relatively small number of 2005 LLY trucks were affected by overheating or 'run-hot' issues. Those that did, were addressed by dealer mods to the airbox inlet, and ECM programming updates. Your product address inlet temps, and also oil cooling. All the cooler, all the better. Hard to argue.

I put 80K towing miles on a 2005 and it never exhibited any overheat issues - or excessive fan clutch engagement, but like most 2005 LLY owners, I noticed a significant decrease in mileage compared to our LB7s, while doing the same work. Hmmm...what changed here? Not the operating temps.

Alan K came here simply asking why his LLY's mileage sucks. If his mileage sucks AND his fan clutch runs excessively, then lets talk about TNFLs. (Thermodynamic Negative Feedback Loops). Otherwise, in the absence of overheating issues, lets talk about things that increase mileage, k?

[killerbee]

Alan K

I see you are from New Mexico.
Where do you do most of your driving?
Elevation?
Did you drive your 01 from the same location?
Is your fan running much of the time while you are towing (summer)?
Do you have a stock intake?
Do you still have a catalytic converter?

[DeezilDoc]

I have an 05 2500 HD extended cab 4x4 8ft box,get 18-20 mpg empty about 14 when towing my 24 trailer

[7.4 VORTEC]

Killer Bee,

On a Duramax, is the IAT sensor in the airbox? I would have thought the computer would want to know what the intake temps are after the air gets "squeezed". If anyone else knows where the sensor is, chime in.

Cheers,
George

[killerbee]

Through 05, the IAT is sensed by the maf sensor, on the tube just downstream of the airbox.

That location has limited value, and I don't know why GM did this. Newer models by contrast, have 2 sensors, with the second sensor located after the CAC. This location is a better place for the PCM to make charge heat and density related timing decisions.

I have a sensor on the compressor discharge also, and some of the temps that come out of the turbo are impressive.

I will assume Alan K's fan runs when he is towing, if he is like every other 05 that tows grades in 100 degree southwest heat. Heavily loaded LLY's that come here , need to leave the valley in the morning to avoid the risk of getting stranded.

The onset of the fan creates a condition where IAT rises dramatically. You get the parasitic loss of the fan, around 20-40 HP, plus the loss of MAF due to expansion. Oxygen density goes down, charge heat goes up, combustion quality has less net positive torque, and economy goes in the toilet. The total net power loss is around 70 HP and climbs higher than this. So speed drops and/or fuel use increases and the ratio of "miles" per "gallon" goes down.

Sure there may be other things you can do to improve economy, but none as dramatic as modifications that keep IAT down, and the fan off. If you don't tow, or live in Northern states, there are other places to look. Reducing cruise boost, increasing cruise timing, eliminating the cat, a larger tire, bed cover, a fuel additive...

One other thing to look at is the MAP sensor. If it is not calibrated correctly, you can be overboosting the motor 100% of the time. The only way I know of to determine this, is to put a separate boost gauge on the intake plenum and compare numbers with the desired boost histogram. Zero boost is required at empty cruise, anything more is a waste of fuel, at least that is what I concluded when I reduced it to zero. Some tunes have boost as high as 5 psi at low throttle cruise.

[7.4 VORTEC]

killerbee,

Where does water injection come into play for a Duramax to help keep it cool if pulling a nasty tall hill with a large load? Forget added horsepower at this stage, we're just talking keeping the motor cooler (which as you claim will give you your potential horsepower to use).
Will water injection help? Are there downfalls to it? Have you had a chance to do any testing with water injection?

Other than the cost of the water injection setup and the pain of keeping a tank filled, it seems pretty economical to keep the IAT's cooler (in addition to the CAI, oil cooler, etc).
Maybe something to run all the time in the summer to augment the CAI for better mpg's.

Cheers,
George

[killerbee]

With IAT containment, the amount of heat rejected by the CAC is significantly reduced, and denser air charge results, note the lower post-CAC temperature in the chart. All of the improved ECT benefits result from reducing the heat load of the CAC in front of the radiator.

The same can be accomplished with pre-CAC evaporative cooling. The cooling value of water comes from the latent heat absorbed when water is evaporated. Just like when your skin cools from sweat evaporation, the air charge cools if water is evaporated within it.

It is not shown in this chart, but COT reached 600 F (IAT uncontained). That can be reduced to 450 with sufficient WMI. I am testing pre-compressor misting in an attempt to determine if actual compressor efficiency can be increased, providing more benefits like EGT decrease.

I prefer optimizing with passive modifications before resorting to consumeables, but this has potential, if you can dismiss the impracticalities. You also need a good supply of demineralized water, since fog is likely to form in the cold side of the CAC. To get an idea, for 900 cfm, or 50 lb/min of air at 20% humidity, approx 1-1.5 liter/minute is used for saturation when it has heated through compression to 600 F. That could be 2-3 gallons for a challenging grade. The heat benefit to the CAC is a rejection rate reduction of over 100,000 BTU/hr. Much like a good CAI can provide. It makes more sense to me to use the CAI (my special recipe of induction improvements), then add effectiveness to it with evap cooling.

To put that in perspective, the cooling stack has a total cooling capacity of around 700,000 BTU/hr. That 100 K BTU reduction is very significant in providing more capacity for the radiator. This discounts the power benefit.


http://members.cox.net/beekiller/GMC%20Light%20Duty/Thermo%20chart%202%20CAC%20Heat.jpg

[7.4 VORTEC]

Killerbee,

Understand your concept of doing the passive fixes first and I agree.

Not familiar with the term "COT". Let me know what it stands for. While your at it, let me know what the CAC and other acronyms you're using so I'm on the same page and not mis-understanding your explanations.

The 100,000 btu reduction with the WMI is almost 15%....pretty good if needed on those hot days climbing the grades into Vegas. Do you think there is some level of very low WMI that can be used the majority of time to further increase mpg's?

Last question. When I was at SEMA last year, Flexilite had a water spray system that sprayed a mist of water onto your radiator (or in this case intercooler). I remember about 20 some years ago a magazine writer (Willy Worthy) in Four Wheeler made his own homebrew version for his motorhome that he used on long grades. Wasn't even fancy (pretty much cooper tubing with a bunch of holes drilled into it) and a nice large water supply from the RV's water tank. Said it worked like a charm to keep temps in check. I do think he was running a big block Chevy at the time.

Do you think you'd get more btu reduction via the WMI or a modern spray system that cools the air to the intercooler, radiator, oil cooler, atf cooler, etc. Or in the end, is the total btu energy displaced going to be the same with either method?

Thanks,
George

P.S. Did you see banks power response to a possible egr issue with the maf sensor and increased airflow in the newer post....any thoughts on how this might effect other trucks?

[killerbee]

Killerbee,

Understand your concept of doing the passive fixes first and I agree.

Not familiar with the term "COT". Let me know what it stands for. While your at it, let me know what the CAC and other acronyms you're using so I'm on the same page and not mis-understanding your explanations.

The 100,000 btu reduction with the WMI is almost 15%....pretty good if needed on those hot days climbing the grades into Vegas. Do you think there is some level of very low WMI that can be used the majority of time to further increase mpg's?

Last question. When I was at SEMA last year, Flexilite had a water spray system that sprayed a mist of water onto your radiator (or in this case intercooler). I remember about 20 some years ago a magazine writer (Willy Worthy) in Four Wheeler made his own homebrew version for his motorhome that he used on long grades. Wasn't even fancy (pretty much cooper tubing with a bunch of holes drilled into it) and a nice large water supply from the RV's water tank. Said it worked like a charm to keep temps in check. I do think he was running a big block Chevy at the time.

Do you think you'd get more btu reduction via the WMI or a modern spray system that cools the air to the intercooler, radiator, oil cooler, atf cooler, etc. Or in the end, is the total btu energy displaced going to be the same with either method?

Thanks,
George

P.S. Did you see banks power response to a possible egr issue with the maf sensor and increased airflow in the newer post....any thoughts on how this might effect other trucks?


I just posted on that. i thing egr is the wrong direction, but I could easily be wrong.

COT-Compressor Output Temp
CAC-Charge Air Cooler, IC

as to your description of external vs internal WMI, internal is the way to go. So much of an external mist is manifested in lower underhood temps, as to make it very impractical as an overheat solution, you have to use 5X the water to net the same result.

As an aside to the 15% concept, if much of this evap cooling can take place before the compressor, or within it, then (in theory) the efficiency of the compression stage can be increased to quasi-isothermal, resulting in greater benefit...and that equates to lower turbo rpm, lower drive pressure, and lower egt. So the benefit is more than 15% because that very activity creates a compression with less heat formation and less work required of the turbo.

Of course the objections seem to be, how do you evaporate that much water without damage to blades spinning at 119,000 rpm?

"Do you think there is some level of very low WMI that can be used the majority of time to further increase mpg's?"

probably not enough to make it a practical idea. Demineralized water is not free. Maybe I am wrong.

[Mark Rinker]

Wow. 1.5 liters of water per minute? What size nozzle with what PSI could possibly atomize that volume of water in that period of time?

With all the work that was done with water/methanol injection for the 6.5L engine, why are the water consumption figures so grossly different, when the 6.5L doesn't even have the advantage of an intercooler to begin with?

Something sounds wrong here. I can't imagine feeding 1.5 liters of water through a Duramax per minute and keeping the fire lit.

Just my farmboy observations.

(By the way - this thread is so far off the original posting, I'd recommend starting a new one, or go back and read the first post and answer his question.)

[rob from bc canada]

As to the original question, 16-17 running empty seems a bit low. I've averaged as high as 19.5 running a fairly steady 60-65, with a bit of city driving at each end of 50-100 mile trips.. It drops off rapidly as your speeds go up and rpm's over 2000.

So, if you're making use of that extra power you have, expect to pay:D

Also, a 4x4 will cost you at least 1 mpg, and depending on how may miles on it, mine showed a decent improvement around 20k miles.

Some easy things to try:

Air up the tires to 75psi, check for clean air filter, change the fuel filter, try synthetic lubes, clean the MAF sensor, drive a bit slower, ....

[Mark Rinker]

Mostly driving a bit slower. I have trained myself to drive the C4500 62mph at cruise. That is about 2100rpm, and yields the best trade-off of mileage vs. speed. If I could drive 60, or 58 it would do even better, but time IS money in any business..


Try driving a tankful at 1800 rpm cruise speed, regardless of ground speed. Look what you get by leaving the engine near peak torque.