1.65 mm timing gets 16.5 MPG

[btoscano]

Hey all,



I have the truck set to 1. 65 mm pump timing and I'm getting 16. 5 MPG driving about 75 MPH on the freeway. That's actual speed. The pump was set at the diesel shop to be on the high end of fueling within factory parameters. The shop said the injectors spray good and are popping at 3350 psi. Fuel filter has 3000 miles on it. The power curve is smooth & there is no visible smoke out of the tailpipe. I loaded the bed with wood and drove 300 miles to VA and still got about 16. 5 MPG.



So what do I need to do to get 18-20 MPG? Try "new math" ?



Brian

 

[Dieselman359]

Cool

In order to get better mileage I'd either slow down or just live with it and leave it alone. Try synthetics and run longer drain intervals to offset the cost, check your air filter, and remember that these trucks are heavy, that ain't bad mileage at all.

 

[Mundgyver]

Slow down 10 mph and do a comparison check.

 

[bgilbert]

Yep keep it under or at 65mph, and your fuel mileage will go up. That or get out and push it.

 

[btoscano]

I figured on leaving it alone, BUT...



There are folks on here that claim 20 MPG at 75 MPH... in a '93 W250 5 spd w/ 3. 55's ???

 

[one_ton]

17.3

i get a constant 17. 3 running around in stop and go traffic. 18. 5-21 on the freeway, depending on the right foot. 2 months ago i was getting 15-16 in town, and 18 freeway. the cause, a cracked thermastat. my motor wasnt getting up to a good operating temp. just food for thought.



Bob

 

[LEggers]

I figured on leaving it alone, BUT...



There are folks on here that claim 20 MPG at 75 MPH... in a '93 W250 5 spd w/ 3. 55's ???

The key here is 5 spd... . If you have an auto you will not get close to that 20MPG inless you have some good money to invest in the transmission. .

 

[btoscano]

I have a Getrag 350 5 spd and 3. 55's also.



Is there some drag occurring I may not be aware of?



I noticed that my front driveshaft turns even when I'm in 2H with the hubs unlocked is that normal?



But based from the first responses I'm doing just fine so no need to think about it.

 

[TKingsbury]

No, your front driveshaft should not turn when you drive. Get under your truck and try to rotate your front shaft, it should turn freely. If not, investigate why. Find out if the t-case or the front axle causing it.

Travis. .

edit: I get in the neighborhood of 20 on the highway if I keep it at or under 70, it starts to go down after that.

 

[btoscano]

I suspected the front driveshaft was turning based on where the oil from my main rear seal leak is going. Here was my "test": In my driveway, with the front hubs unlocked and in 2H, I can turn the shaft freely. If I attach a rope to the driveshaft, it will coil up as I go down the driveway.



Brian

 

[AKimmel]

I've seen them turn before on other trucks with NP205's, but kinda just free spinning. You could see it through the floor board. I think it's just the thickness of the oil, and how freely it turns that causes it to spin. If you tie it off to the frame, will it break the rope?

 

[hotram03]

I'm getting 20. 973 mpg around town with a small amount of highway miles, but mostly city, its got 3. 54's and a 5-spd, I'm blowed away by the fuel mileage this ole truck gets, I've been using Seafoam fuel conditioner in it in double strength and its really helped this truck alot, trucks stock except K&N,16cm turbo housing, took off the muffler. That Seafoam has made my truck alot more peppier, I'm currently running thru my 5th tank since buying the truck 3 months ago.

 

[btoscano]

Yea hotram, the trucks do real well in the city & sitting in traffic! I think my Jeep 4. 0 takes 2 gallons/hr @ idle and the Cummins maybe 2 pints! Seriously I have sat in traffic on I-75 coming out of ATL for an HOUR to go 2 miles and I got same fuel economy as I would normally! Same for sitting in traffic around Roanoke for 2 HOURS!! The complaint I have is the 75 MPH driving on the freeways! I guess I should just not worry about it!

 

[BushWakr - RIP]

In one of the previous articles in TDR mag (I think the article was done by Joe Donnelly) the best overall fuel economy was found when the engine was operated at 1700 RPM. This provided the best performance and fuel economy.

Maybe the highway speed/city driving issues can be addressed by using that 1700 RPM solution... . just a thought. .



pb...

 

[91W350]

My 1993 W250 does not do as good as my 1991 W350 does. I usually drive about 65 to 68. My old D250 would get into the mid 20's, but these 4x4s usually run 19 to 21. If you are getting 16. 5 at 75, I am betting you are pretty close. Mine usually drop into the 17 to 19 range at 75 to 78. They will not do that good with a stout cross or head wind. Glen

 

[pepecat]

well once I get the speedo working and calibrated I will let you know how the getrag g360 rsp and 3. 07's do. that could be your ticket

 

[btoscano]

Is that indicated or actual? My speedos on my '90 and '93 are both 5 MPH off!! I am quoting ACUTAL speeds... I am pretty sure my '93 W250 would still get 22+ if I went on secondary highways with 55 MPH speed limits. I got 22+ between Portland, OR and Arcata, CA on 101 !! On TN freeways you'd get blown off the road at 65.

 

[BigEasy]

The key here is 5 spd... . If you have an auto you will not get close to that 20MPG inless you have some good money to invest in the transmission. .

I got 20mpg coming home from TN last weekend... 70-75 mph most of the way, with a 4x4 auto (stock)

 

[btoscano]

70-75 indicated is about 65-70 actual so 20 MPG should be pretty close to correct.

 

[BigEasy]

my speedo is dead nuts even with the DOT radar signs... the tires are 285s