Facts.....



I bought the truck one year ago.

It was just getting cold.

I did not use the ac unit.

6 months later summer arrives.

I use the ac all the time.

Mileage drops a lot. I just didnt put it all together.





So heres how I figured it out.

I drove to the x-prize with the ac off and kept it at 2k rpm cruise
control the whole way. It was 130 miles and I had topped it off before
I left. I topped it off when I arrived and I got a wopping 20 mpg. WOW
! And this trip was up hill about 1/3rd of the way.



So the trip back I run with the ac on and 1/3rd downhill with cruise at
2k. I top it off when I get home and get 16mpg. (downhill)



So if you add level with about 2300rpm's and there is the 14 Ive been getting on the freeway.



Also its the 9-12 I was getting in town. AC on and stop and go.



Hard to believe the ac drops the mpg 4 miles per gallon.





Is that normal?



Oh and my "service 4x4 unit" message comes on. Lost all use of 2wd,4 high, 4 low.........argghhhhh http://www.dieselplace.com/forum/smileys/smiley11.gif

Dude your luck does suck.http://www.dieselplace.com/forum/smileys/smiley5.gif


How cool was that today? It must have been something to have been there. The trophy is out here in St. Louis, that is as close as I have come.


About your mileage, we drove out to the Outer Banks with AC on the all 16hours. and had no change in MPG.


Good luck with truck.

Facts.....

I bought the truck one year ago.
It was just getting cold.
I did not use the ac unit.
6 months later summer arrives.
I use the ac all the time.
Mileage drops a lot. I just didnt put it all together.


So heres how I figured it out.
I drove to the x-prize with the ac off and kept it at 2k rpm cruise control the whole way. It was 130 miles and I had topped it off before I left. I topped it off when I arrived and I got a wopping 20 mpg. WOW ! And this trip was up hill about 1/3rd of the way.

So the trip back I run with the ac on and 1/3rd downhill with cruise at 2k. I top it off when I get home and get 16mpg. (downhill)

So if you add level with about 2300rpm's and there is the 14 Ive been getting on the freeway.

Also its the 9-12 I was getting in town. AC on and stop and go.

Hard to believe the ac drops the mpg 4 miles per gallon.


Is that normal?

Oh and my "service 4x4 unit" message comes on. Lost all use of 2wd,4 high, 4 low.........argghhhhh http://www.dieselplace.com/forum/smileys/smiley11.gif


I don't see any noticable difference in fuel economy with AC or off. 4 MPG is far from normal from what I have seen. I would do a test looking at instant MPG or straight flat driving for short distance resetting average MPG to see if you can replicate the same loss in mileage. Seems very odd to say the least.

I thought I read a post a long time ago about low MPG


being caused by a bad thermostate not maintianing proper


engine temp. This could be effected by the AC as well?

There is no way the a/c compressor is costing your 4mpg. There have to be other issues involved.

Arggghhh



Well thats why I never considered it because I could not believe it would do that to my mpg.



The truck has so many problems right now Im thinking of selling it.



I still have not had time to take it to the dealer. I have a list of 15
seperate issues including speedo broken, gas gauge broken, 4x4 broken
and 12 other tsb's.......

I always run the A/C. Similar truck,,, ie. CA emissions package. Always get approx 15 mpg around town and 18-19 mpg on highway. As others mention, I don't believe the A/C contributes that much to your mileage dilemma.


SpaceShipOne looked pretty cool!!

My mileage has gone down the tubes here lately. Used to get 500 mi between tanks, now it's around 380. Havent figured the actual mileage used to be a shade over 17. now?

I drop about 2mpg when running the A/C.

The AC would really drag down my mileage in my 99 6.5TD - but I haven't really seen it noticably impact mileage in the DMax.

Im getting 17mpg with normal good driving habits. If I kickit around a little mppg drops to 15. The air conditioner doesn't seem to matter, its on all the time. I use Shell Premium and if I switch to Exxon or Shamrock MPG drolps 1-2 mpg. Addoitives don't seem to help much.

I don't think this is too unreasonable that the A/C would cause this difference. But, if it is affecting this much, it is not working right.


Consider how the A/C is performing when you use it. Does it cool well? Can you adjust the outcoming air temperature? If the A/C is always running the compressor it will cool the system a lot and freeze up which will increase your pressures. If the compressor is also very tight (can you easily turn the compressor shaft by hand?) Mine is easy to turn by hand.

It's almost as if the AC unit is affecting the fuel/Air ratio. I know it sounds crazy...... but, if the fuel is rich the N03 will come down do to lower EGT temps on a stock truck. Well, that's what I gather. Could this CrAzY idea have any validity?..... I doubt it, but it does seem like the problem.http://www.dieselplace.com/forum/smileys/smiley5.gif


When you, if ever, get this worked out.......... DO TELL. I bet you could sell the info! I know a few folks, such as myself, that don't get squat for MPG. My AVG refill is around 310 miles.......really sucks.





Burner----------------> http://www.dieselplace.com/forum/smileys/smiley4.gif

IF...I keep it below 2Krpm and if I don't run the air, I'll break 20mpg. I'll lose about 1 1/2 mpg with air on. IF....I drive more my normal way, with air on around town 17.5mpg.

I can't really believe a 4 MPG difference either, but running the A/C on my truck will easily lower my fuel mileage 1.5 to 2 MPG on long highway trips. My wife gets mad at me when she's in the truck, because I'm always wanting to shut the A/C off & roll down the windows. It'll mess up her hair! http://www.dieselplace.com/forum/smileys/smiley13.gif http://www.dieselplace.com/forum/smileys/smiley29.gif

Was there a head or tail wind on either leg of your trip, PC, that could have affected your mileage?

small AC....small headwind.... affecting a 300HP motor with 520ft lbs of TQ... doesn't seem likley. Why would an AC unit not affect the 1500 series like that? Heck, if it had the exact same affect...we would have a really weak motor IHO.

no wind except a breeze from the side

Consistantly my mpg will drop when I hot rod around town or run the interstate 70-75 mph. Lately, I've been keeping the speed to 63 mph(1950 rpm) down the highway and get 20mpg.


It only hurts the oil guys to drive slower. http://www.dieselplace.com/forum/smileys/smiley2.gif

A/C costs me mileage. I also try to keep it off of defrost because that also cycles the a/c compressor. I would say it is more like 1.5 mpg. But it definatley makes a difference. Find a long straight highway turn on your DIC and get an average then turn it to a/c or defrost and you will see your mileage drop.


Oh yeah, my wife does the same thing cause I want to get that extra 1.5mpg.

When I got my truck I got 16.8 in the city with no A/C, cooler temps usually do about 45 in the city. Come summer my milage has dropped to about 13 with the A/C on all the time. My only highway trip I have taken yielded 19+ mpg cruising 76 mph with the A/C on all the time going thru the desert over a pass.





We will see if my mileage goes up as the temps are finally starting to get cooler. Got to hate the summer here in sin city.

I see no difference in MPG with AC on or off. Consistently 20.5-21.5 mpg on the highway. This is 65-70mph with cruise on.

I easily get 500 miles to a tank on a highway run by using cruise and keeping the RPM at 2000 or below. 2000 RPM gives me 65MPH and that's fast enuff.


This was the result i always had from when the rig was brand new.I did a run to Alaska this spring and on the return noticed that i was really going thru the fuel quickly and thought it was the headwinds,hills and mountains etc ,until i got home and a week later had it in for 8 INJECTORS REPLACED.Since then i have been getting 22-23 MPG(CDN) driving the same as i always have .I now with Greg's Racor fuel system in place and i will continue sensible driving and hope for the best.

I have found and many have stated that the Dmax mileage is very sensitive to RPM's Especially once you get above 2k or so.


You do an extended freeway run at 75 or better and your mileage will tank (no pun intended).


GM is famous for the 90hp compressor, with my old 5 liter half ton I needed to turn it off to pass someone. So I believe that the A/C does have a noticeable impact on performance and mileage...how much I don't know.

Believe it or not, the newer compressors are supposed to have less of an impact on fuel mileage than the increased drag of driving at highway speed with the windows open. I can't back that up, read it somewhere a while back, but it's not too hard to believe.

While I don't doubt that there is some difference in MPG with the A/C
off and on, I don't think mine is anywhere near 4 MPG, probably less
than 1/2. Very hard to measure. IIRC, A64pilot is right on the money . There was a study
completed that most vehicles actually get better mileage with the A/C
on and the windows up than they did with the A/C off and the windows
down (at speed, not stopped).



You can see how much difference in load there is if you have and Attitude (so that would leave you out PC).



Set the Attitude to show load %, kick the A/C on ,record load, kick it
off, record load again. I see about 2-3 % difference in engine
load with A/C off and on. I usually kick mine off to help cool
down the turbo faster when I go to shut the truck off. I haven't
however looked at engine load to see if there was a difference with the
windows down,. That would be a much harder test for me, since
you'd need a good long stretch of level road on the cruise control
where you could test it.



Dennis


Edited by: baimpala

I suspect there is something else wrong with your truck. A 4 mpg drop cannot be explained by the use of the A/C button. I just came back from a trip to Monterey. I refueled before completing the return trip, but the tank covering most of the driving included about 230 miles of freeway driving and about 130 miles of mixed city and two lane roads. I had the A/C on about half of the time. On the freeways I held 75 with cruise on. Over Pacheco Pass, which has a fairly steep (though not challenging climb) 70, again with cruise on. On the divided, high traffic and 2 lane roads I went whatever the traffic would bear, which varied between 55 and 65. There were a few, isolated full power blasts while passing other cars as well. I averaged 18.2 mpg for the trip. I've made similar trips with the A/C on the whole time and not seen a big difference in mileage.

TC

I don't think it affects the steady highway driving. Mine gets great keeping the cabin at 75 deg thru the desert while cruising 75 mph.


However since it's been cooling down here in sin city I havn't been using my A/C hardly at all and my mileage has gone up quite a bit. Havn't had to fuel up yet (was out of town for a while, military stuff) but I do know that acording to my trip I should have fueld up a couple of days ago and I have just between 1/4 and 1/2 tank left. There has been no change in my driving style either, just no A/C

I get about a 1.5 to 2 mpg drop running the A/C.


But, I don't notice it due to the Dmax's high amount of torque.


The A/C compressor will take a good amount of power to drive.


The old rule of thumb for automotive A/C's is that they are about 5 ton compressors. For you guys that have central A/C, the average home A/C unit is about 2-2.5 ton units for a 2000 sq. ft. house.


I think that PC's accessories might add up to his mileage loss.


Also could be other things. It will depend on climate, local, etc.


I have noticed over the past 9 months of ownership of my truck is that mileage is REAL dependent on driver, climate, wind, and load.

"I have noticed over the past 9 months of ownership of my truck is that mileage is REAL dependent on driver, climate, wind, and load."


I believe altitude has a lot to do with it also. I live at 6000 Ft. My average tank concists of 50% city 50% freeway with may trips over 80mph and many averaging less than 72 mph. Flat out cruising to Califorina earlier this year gave no better than 16 MPG at 75 mph.


After 15000 miles I have maybe had 10 refills that I was able to get more than 300 miles to a tank. I don't have any problems with my truck other than the "popular" problems that the reflash is supposed to fix. I just always get BAD mileage. Mostly I see 10-11 mpg around town and 14-16 mpg on the highway. My lifetime AVE. MPG from the truck is 13.6 and as I said thats on 15000 miles. I do pull a load about once a month, and I have the Attitude now that I have had to remove due to the severe engine knock. Edge says to get the reflash done and they believe my problem will go away.


By the way, the Attitude lowered my mileage by 1.5 to 2 MPG and A/C doesn't make as much difference as adding fuel additives does. Also, my truck is faster on level 4 than it is on level 5.http://www.dieselplace.com/forum/smileys/smiley5.gif I could not spin my tires until I hit second gear on any setting.


2004.5 LLY CC SB Ali 15600 MI. EGR disconnected, all else stock.