decress in MPG

[tmg115]

i have noticed a decress in my MPG. i was up in the 17's in the city and now i am at 15??? and also i was in 20-23 mpg highway and now i am at 19??? any inside to this?

[Big O]

You still have me beat! :mad:

[Alli-max]

How long has it been going on? You getting fuel from the same location?

[motovet]

Warmer drier air? The current #'s are the BEST I have ever seen.

[ 06-16-2002: Message edited by: motovet ]</p>

[Smorey]

Air filter getting old?

[redneckcowdoctor]

My experience was similar: Consistently in the 19's for the first 5k, then decressed to about 18 mpg now. Diagnosis was simple. After seven gas pickups this was my first diesel. Quiet as the Duramax is it is still quite a bit louder on acceleration than the 350 cc gas engine. Initially I drove the truck like an old lady (sorry mom) due to my unconscious reaction to the noise. (I read posts about the the sound of the pilot injection shutting off--I'd never heard it, I'd never reached 2500 rpm!). Once I figured out that the accelerator could be pushed down further than 1/2 inch without damaging anything my fuel milage decreased while my driving enjoyment skyrocketed. I now look forward to every interstate on-ramp and the chance to "blast off".

[3176CATPOWER]

Did it drop after you put that 100 HP chip in?The mileage you were getting is really above average.Mine was running close to 19 then dropped as yours did.The last 1200 miles it came back up,19.6 mpg average.Dont know if the fuel got better (SAME SUPPLIER)but truck seems to running best yet.

[Diesel to the MAX]

Your "bad" MPG is about what I'm geting now.

On another note, we all should see a slight increase in MPG in the summer months. This will be caused by getting beter fuel at the pumps. During the winter months they thin the stuff out so much, it's a wonder the trucks run at all.

[DMAXDiva]

Check that air filter!

My stock filter was PACKED with fiberglass insulation...I really do think it came from the factory this way (though I can't prove it :mad: ). Can't tell if the mileage has improved with a new filter, cuz I added Juice at the same time and I can't keep my foot out of it! ;)

[tmg115]

it just started about 2 tanks of gas ago. i have about 6,000 milles on her. and i have used the same gas. it is just wierd.

[KenZ]

tmg,

"it just started about 2 tanks of gas ago. i have about 6,000 milles on her. and i have used the same gas. it is just wierd."

That gas will do it every time!! LOL

Ken

[James S]

Hey Folks,

I strongly recommend that everyone read the article "BREAKING IN A DIESEL ENGINE". It gives a vary extensive and DETAILED procedure of how to PROPERLY break in your new diesel. The website address is:
www.ford-diesel.com
Go to articles, then it is about five or six down in the list. I think people are forgetting that your milage will jump around for the first, potentially as much as thirty-thousand miles. If you look at the MPG post, this is proven, that those with trucks with twenty to thirty-thousand miles on them, are FINALLY starting to see the milage settle down. Your average range from this point on, [based on reading I have done on this website and others] is that you should be getting sixteen to eighteen in town and twenty to as high as twenty-two on the highway. This is using the American gallon. Canadian owners should take their milage and multiply it by 1.2 to convert to the Canadian gallon.
[3.78 times 1.2 = 4.55 litres which is the Canadian gallon, rounded up from 4.545454] So, Canadian owners should be getting about eighteen to twenty-two in town and twenty-four to as high as twenty-six or maybe even twenty-seven on the highway. Also, do not forget that those of you with add ons like, truck caps, accessory bumpers, winches, large mirrors, etc, could experience decreases in milage, but they should be slight. Also, the six-speed manual transmision, is proven to give as much as two to three extra miles per gallon, MORE than the Allison, due to the extra gear, thus lower Rpms, and having more control over the RPM levels. Good luck and enjoy your truck[S].

James

[JLee]

Wish I could get what most folks post here!! I average 14.8 - mostly city with a bit of hwy and a little towing of a 7000lb fifth-wheel. Best was 17.something a long time ago. I'm going to be taking a longer road trip in late August (empty) and I'm looking forward to seeing what I really get running multiple highway tanks. I think I drive it like that little ol' lady mentioned above most of the time.

[turbolag]

My truck has never seen better than 15 mpg in the city on the hwy empty or loaded. I have approximately 16K miles on truck with an average fuel economy of 12.8 mpg. This truck is stock. Any suggestions????

[James S]

Hey Turbolag,

Did you read the article i suggested people read? In there, there are some hints as to why you are getting such brutal fuel milage. I agree this is almost unheard of with a diesel. Read the article because I cannot type it all up here. Other things I can think of are your filters need changing, or you are getting bad diesel from the station where you fuel up, or something is wrong with your air sensor, or your MAF sensor [I think that is the correct spelling] is dirty and needs to be cleaned. Does the truck seem to be running fine? What transmision do you have? Is it working well? Maybe you should try and put a Kenedy exhaust on the truck. Everyone seems to think they help fuel milage significantly. Keep us posted.

James

[turbolag]

James,
Thanks for the response. I've had the truck into two dealers and they said no problems, average the fuel economy out over 6 tanks of fuel. When I showed him that I had fuel economy #'s from the first tank to present they said they did not know what to think. I'm putting in gauges this weekend and soon juice so I will keep you posted.

David

[James S]

Hey Dave,

That is good. In this same thread, three posts above this one, I posted an article to read about breaking in a diesel engine. If you have not read it, I strongly, strongly, encourage you to read it! It has some reasons as to why you MIGHT be getting the extremely low fuel milage you are experiencing. Read it, and let me know what you think. I wait anxiously for your reply. Hope to hear from you soon. Anyone else who is getting, or has recently purchased a diesel, I also encourage you to read this article as well. You will understand why I am so persistent about all diesel owners reading this article, once you have read it.

James

[N.E. TMRPR]

Here's my own observations on mileage with my truck. I bought my truck last July and got great mileage all summer long {19- 21 highway}. As winter approached my mileage decreased to 17-18 mpg's and sometimes less. I have my own fuel delivered and it lasts me a long enough time to know it's not winter fuel causing the decrease. As the spring came we had a few hot days for us in the northeast{5 days in the mid to high 80's}. My fuel mileage immediatly went back to what it was the previous summer. When the cold weather came back my mileage went south again. Same fuel, same filters, same everything but temperature. We are finally getting some warm back here in New England again and my mileage is back. Looking at the posts it seems most are from the cooler climates but not all. Try observing the temps when you have good days and bad days. It seems like these trucks monitor the outside temps and apply fuel accordingly. Does anyone have an idea or has anyone also experienced this.

[James S]

Hey Folks,

When the temperature outside is colder, your diesel thickens. As a result, it does not burn as well, thus giving you slightly poorer fuel milage. The way to overcome this is to keep the truck indoors at night or whenever possible, however not vary many of us are able too. When the temperature warms up outside, the fuel returns to its normal vescosity, thus burning better, and giving you back the better fuel milage that you lost during the winter. This is not an issue with gas powered vehicles, because gas is not NEARLY as oilly as diesel. It is the oil which thickens up in the cold.

James

[tmg115]

i was thinking about it and i just figured it out :D i never used my ac before the summer and now i am really using it so that has to be it. i can't believe i didn't think of that :D

[afp]

James,

I read and and downloaded the article. My truck had 200 miles on it when I bought it--probably from test drives, so I can't speak for how it was treated then. I have now put a tad over 1000 miles on it, and it appears I have done it right. I have driven in the city, on the freeway, and on country roads both in the hills and in the valleys. I guess I need to find something to tow so I can load the motor and get it hot. I just don't have anything to tow right now.........

Blaine

[James S]

Hey Folks,

I spoke to a Duramax rep at an auto show back a few months ago, and another fellow asked that vary question about the AC affecting fuel milage, and he indicated that it would NOT in any way. I hope this is reassuring. If it is affecting people's fuel milage, let us know, and I will pass it on to him. [if I can find his business card, with his e mail address on it]

James

[mackin]

James S ,

Well, let him know he is full of, DO, DO ....... Or your choose of words . Ac effects every engine in the form of a load, strain . It will grab and take away power. All though not really felt in the D-MAX, but it will lower mileage ....

MAC smile.gif

[ 06-27-2002: Message edited by: mackin ]</p>

[NEW2DMAX]

2001 2500 HD CC 4x4 W/ Allison 10,000 miles, I will ave. about 16.4 to 16.6 mpg 50%/50% city/hyw. Approx 17 mpg on the Hyw. tongue.gif

[NEW2DMAX]

OOPS HWY not HYW
:D

[Idle_Chatter]

Well, I found that using the A/C really impacted my fuel mileage in my '99 6.5TD Tahoe (to the tune of 3 or 4 mpg!) but I've been running the A/C full-bore 24/7 lately here in Maryland in the DMax and my mileage has been between 18.9 and 19.6 stop-and-go! I used to lay-off the air until it was at least 85-90 degrees in the Tahoe, not a problem in the DMax!! tongue.gif

[stretch]

I agree with Mackin, use of a/c must affect mileage. The question is how much. IMHO, use of a/c is either the same as less than opening windows and driving down the highway in terms of strain on the engine - compressor vs. aerodynamics. Todays compressors are far less HP robbing than the ones from years ago. I say use it and accept the losses (which are minimal).