What happened to my MPG!?

[DevenWood]

Here is my story. My typical mileage is right around 12. 5 (hand calculated of corse) it sucks, but its acceptable. When I leave town I turn everything down so the wife can drive it. (smarty to stock, TST-Econo 0/0) I got back to town and figured the mileage and its down to 9 mpg!



No smoke other than normal, seems to run fine. I do have the cooldown set to 250 deg. so it idles about 5 min. before shutdown.



Any ideas, things to look for? Thanks in advance

 

[jmorse]

Maybe the truck was used harder than normal or it was driven so little that the average mileage is not as accurate as over a longer period. How many miles was it driven?



Jim

'05 2500 SLT, QC 4x4

'07 3500 C&C SLT 4x4

 

[BHolm]

I think you are wasting a ton of fuel by running it down to 250 degrees. I also think you are doing more harm than good by idling so much. You need to cool the turbo down but I would have it set at 350 degrees max. With all that idle time I hope you either use oil analysis or change pretty often.

 

[rjohnson916]

I think you are waaaaayyy overkill on your idle-down time. I tell my wife 375 and shut it down, I use that fig as a good ol rule of thumb, but when we are in a hurry it's more like 385-390 ish.



-Ryan

 

[TMConroy]

Mine was at 12. 27 highway. Try getting your ECM reflashed as I did. When I purchased my rig it was at Rev E. Now it is at Rev S. Starting to see changes in mpg.

 

[Mhannink]

you guys its not the idle time that we are worried about right now his mpg have dropped even though he is idleing the same. yeah it may contribute to the overall bad numbers but this post is about figureing out why it has recently dropped. devenwood your truck is new im guessing with an 06 you probably have 35k 40k miles on it if that. the motor could still be tight especilly if you dont tow much. i know my buddies 04. 5 is like that its got 60k on it and its still breaking in as the milage is still improving ever so slowly. as for why it dropped suddenly i would try tmconry's sugestion and get a reflash that may help i dont know.

 

[AFellows]

When you set Smarty back to stock you are losing some mpg. Maybe that with the extra idling is accounting for your lose. Does your wife have a lead foot?

 

[Bodie]

Does your wife have a lead foot?

That could be a good reason. :-laf Pulling all the modules and programmer is what mainly dropped the mileage, next time put the Smarty on 1, and set the TST low. That will help the most, also how many miles are on the truck?

 

[betterthanstock]

Short trips. If you drive for 10 miles, with a cold engine (it takes about 7 or 8 just to get the water temp halfway on the gage), then let it cool down for 5 minutes, what a waste of fuel!

Reset your mpg gage when you first start up, then as you idle away down to 250 degrees, watch your mpg go down, down, down. .



Why not use synthetic oil and set it to 350 instead?

 

[wcjp]

Does your wife have a lead foot?

My mileage always goes down when the wife drives.