Engine/Transmission (1994 - 1998) 1997 2500 MPG Improvments

[Fish On]

My brother-in-law is saying that his '97 has a recent drop in mpg, down to approx. 12. 5mpg empty. It used to get a constistent 15-16mpg. He hasn't changed tire size recently and it would get 15-16 with winter fuel so that can be ruled out. My brother-in-law is not mechanically inclined so I'm sure so things need to be looked at. Do you have any suggestions, maybe some kind of a checklist of things to look at so I can go help him out. BTW the truck has approx. 80,000 miles. What size tires did this model year come with stock? Maybe if he has different size there could be some correction factor. Anyway thanks for the help.

 

[ata]

97's came with 245-16's As for a drop in fuel mileage my 97 lost about 2. 5 in fuel mileage in December and has not come back. I'm wondering if they have changed winter fuel to even less BTU's.

 

[TurboTweaker]

Try adjusting the valves, and checking the timing. i know it helped on my dads truck when it took a dive. 18 mpg city now.



The Fat Kid

Andy

 

[mikel]

Do the basics first.



Air filter

Fuel filter



Then do the valve adjust and check the fuel pressure. A bad overflow valve can cause poor mileage.







Does the truck seem low on power too?



Mike

 

[Vaughn MacKenzie]

I've had the opposite problem. . . my '96 strangely took a MPG jump, and I'm not sure why. Nothing like driving habits or anything has changed, just that the weather got pretty cold. Last tank was 19+ with about 1/3 of it commuting around town. I thought I underfilled it, but the current tank is dropping slower than usual. . . to the tune of about 17. 5 mpg. It's just under 1/2 tank and that's been nothing but driving around town.



Vaughn

 

[towner]

I used to work in a shop when I was in my 20's and the owners son had all the goodies... . he put a 500 cid engine in his chevy truck and was crying about the mileage so he put EFI on it and still *****ed so we started siphoning gas out every day and he kept pulling parts off the shelf and his mileage was down to about 4 mpg. He was going to pull the engine so the tuneup guy told him the dist advance was probably stuck and he recurved his advance . Now we started his mileage on the upswing as he tuned and tuned we kept putting gas in till he was up to 21mpg with his BB fullsize truck. He wasn't happy when we finally told him but he didn't flaunt all his toys as much.



I know its not something you'd think to look but do you have any jokers in the midst. Thanks by the way for reminding of a good ole joke

 

[VicR]

but the current tank is dropping slower than usual. . .



Vaughn

Or the float is stuck



Seriously, when you figure out the secret let me know. Diesel just finally dropped below $2/ gal here and I could use all the MPG I can get.



-Vic

 

[TrqMonster]

My friends 01 is taking a dive in mpg. It only happens when it gets really cold like 20* and below or so. When it warms up it goes back up. Its a big drop, I think like 4-5 mpg. Any ideas?

 

[GRW]

Mpg

My MPG went down with the cold weather.

But when I think back about how good the MPG was with my chevy.

79 crew cab, started out with a 350 in it (hauling a 11. 5' camper).

Put a big block in it, the MPG couldn't get much worse.

My Dodge will run circles around the old CC and gets 2X's the MPG.

So I am Oo.

 

[Dr.Bob]

It allways goes down in the winter, they mix No 1 with No2 Plus your warming up your truck longer. Go find some stright No 2 put in some cetane booster it should come back up some.

 

[TWilkening]

Okay the guy had a built big block and he's complaining about the mileage?!?! Hello!

 

[nfox]

Fuel Mileage

i would suggest checking the fuel pressure and check the timing, if it dropped off all of a sudden i would bet the timing has slipped. just my thoughts.

 

[jtwcummins]

Take a look at the fuel lines, in the starter motor area, they have a tendency to start weeping after a few years. Mine were and replacing both feed and return got back most of the MPG lost, 13-14 went to 10-11 in town. I have had my CTD since 1/97 and MPG was consistant until about 6 mos ago, just seemed to drop overnight. Did the fuel filter and cleaned the AFE air filter, no help.

Also, clean the fuel heater pre filter. This is almost always overlooked.

 

[TKohler]

I see a couple of mpg drop in the winter time but i think its just letting it warm up a little longer when its cold outside .

 

[Fish On]

TTT Thanks, Anymore suggestions

 

[WDaniels]

There is something else for the cold weather guys. I'm used to driving in weather that is -30,-40,-50 degrees every winter. And thats not with wind either. During the summer, at 65mph, I pull about 2. 5 lbs of boost to maintain that speed. During the cold weather to pull that same speed, I pull almost 10lbs of boost. And as everyone knows, boost=fuel usage. What everyone mostly forgets is that when it's that cold out the whole truck resists moving and once you get it moving, it takes alot to keep it that way because it's so cold out. So, alot of the time there isn't anything wrong with the rigs cept theys is just cold, cold, cold. Heck, when it hits about -35 when I apply the brakes, it takes about 10 seconds for them to release from the calipers. At -45 and the truck has been sitting all day, the tires will develope a flat spot and takes about 1/2 mile to re-round. If you go around any corners you get a rolling jolt for that distance. If no corners then you just bob up and down in your seat until they re-round. It's funny sometimes.



WD