Diagnosing poor fuel economy..

[TX Gooseneck]

Not sure on the RPM at 75 (Auto, no tach) This is my backup truck, I typically drive my 04. 5. I commute about 80 miles one way, so 75mph is a MUST!

 

[JLEONARD]

I think the right foot has the largest impact on fuel mileage. My $0. 02 Dan

That is absolutely correct.

A diesel engine is a precise machine that uses fuel based on horsepower used... . not on horsepower available.

Now were up to $0. 04

 

[bgilbert]

Club cab, auto, 4. 10's almost the worst for mpgs, if you had a 4x4, then you'd have the worst for mpgs. You sound about normal for your truck and the speed at which you drive. Run 65 for a week, see how much your mpgs go up. New injectors will in most cases increase fuel mileage. I agree the right foot has the largest impact on mpgs.

 

[MFalkinham]

Club cab, auto, 4. 10's almost the worst for mpgs, if you had a 4x4, then you'd have the worst for mpgs.

(in best Homer Simpson voice)... ... ... DOH!!!!!!! :{



Actually, it can get worse than that..... add in my dual rear wheels for more weight and rolling resistance! Even with all of this stacked against me, I'm still very happy with 15mpg. I just imagine what how bad it would be with a 440 big block!

 

[cerberusiam]

We get so enamored with the HP we are chasing we somtimes forget the power doesn't come without a price. Add to that the trucks we drive have the aerodynamics of a box car and its a testament to the design of the Cummins we get the mpg with an engine that is archaic by todays standards. Look at the mileage of the newer trucks and it hasn't changed that much yet the power has doubled and enissions are down. As Mr Loaf says "2 out of 3 ain't bad".



Mileage on gas trucks I have owned:



1961 D300 Dodge truck 5 sp 6. 80 rear gross 18k - 9 empty 3 loaded.



!977 D100 2x4 440 auto 3. 55 rear - 10 no matter how fast I went.



1984 W250 4x4 4 spd 3. 55 rear - 10 empty, pulling a 24 ft gooseneck gross 18k 7 on a good day.



Early 1991 W250 CTD 5spd bone stock 3. 55 rear - 19 to 20 empty/light load, 11 to 12 pulling trailer gross at 18k.



1992 D250 CTD auto 3. 55 rear - 20 to 21 at 75-80 mph, avg 11 gross at 16k with a best of 14 at sea level with same load.



1988 Suburban auto 4x4 3. 73 rear - 12 to 13 empty at 75, towing with gross about 10k 6 mpg.



1996 1500 360 ci 3. 55 rear - 14 to 15 at 75 to 80, 8 towing anything.





See the pattern? The worst I get with the CTD is still almost twice as good as the gassers. I will settle for the 16 to 17 I am now getting knowing full well the injectors need attention, the trans is a big problem, and I can't keep my right foot under control.





If we were really that worried about mpg we would be driving Geo Metros , NOT!!!!





TXGooseneck, I need a trailer preferably a gooseneck. Send me some info, thanks!

 

[Hunter4x4]

Taller tires have the same effect as going to a lower gear, i. e. , from 3. 55 to 3. 43. Your speedo will read slower than your actual speed and your odometer mileage will read less than actual traveled milage. (Like my '78 Jeep on 35" Swampers - speedo reads 35 MPH, I'm actually doing about 44 MPH!!!)



I check all my vehciles speedo's and odometers with a GPS, and when I brought my '91 home with the stock P235-85 16's (about equivalent to a 32x9. 50-16 tire) both were about perfect.



When I went from the stock rubber to P285-70 16s (roughly equivalent to a 33x11-16 tire) my speedo affect was negligible but my odometer mileage needs a correction factor now of 1. 02.



Hope this helps!!

 

[MrWinkey]

Well it depends like alot of people say.



My 92 with the pump turned up I get between 20-24 unloaded.



The wifes 93 completly stock gets 18-20 unloaded.



Nearly the same truck... ... only thing I can think is it might be the tires... .