mpg discusion

[pitsingerk]

This has been discussed on here many times probably, but I want to bring it up again now that diesel here has hit 4.19 a gallon. I have 97 Sub w/ automatic and 4:10 gears. I've replaced the injectors due to having approx. 130k miles on them and I'm saving up to replace the injection pump also for the same reason. I have a couple items I plan on doing in the next couple weeks to try and get better mpg, right now it's getting 14-15 around town, 17-18 on the highway. I want to run this by the forum for good / bad feedback. First thing I'm going to do is remove the cat and muffler and straight pipe it. If it's too loud I'll put in an aftermarket muffler. I'm then going to find an electric fan setup out of a silverado to put in it, I've heard from a couple people this may be good for 1/2-1 mpg. My next step, and this is the expensive one, is to change out the gearing to 3:54's. I don't pull much with this truck and use as a way to haul the family and soccer/softball teams around. I have my other truck to do the heavy pulling. Any feedback will be appreciated and also any other ideas would be great.

 

[DieselSlug]

The mileages your getting seems very good with a burb and 4.10's. I have 3.42's in my truck and am glad i do. Electric fans havent quite won me over yet on large vehicles, would stay away from those. A 4'' exhaust will help. Keep your vac. setup on your turbo for best mpg's.

 

[pitsingerk]

What mpg are you getting with the 3:42's. I'm not uphappy with the mpg numbers I'm getting, just unhappy with the 4.19 a gallon and we all know that it's only going to get worse.

 

[DieselSlug]

I am getting high 16's to low 17's around town. On the highway i get high 19's. But i am not running as efficient as i should. My thermostat is a 180, runs too cold all the time (need it for the plow, used to overheat a lot). And my turbo master is setup for peak boost at 14 PSI, going to tune it down for economy reasons soon.. I have a multi tune chip, and in economy mode it bumps it up more on each side. I keep it on a tune thats setup to be a bit over regular performance but trying to retain a decent fuel mileage.

 

[great white]

My 98 ECLB K2500 with 4:10's gets an average of 13 mpg combined.

I've got fuel records going back almost a year and that's what it's calculated from.

I feel your pain, but I wouln't expect much more than 20 MPG highway form the old girl.

Even at 17 mpg, that's nothing to sneeze at for a 397 cid engine pulling all that sheet metal and glass around.....

 

[handcannon]

I'm going to be watching this thread closely. I'm currently getting 13-14 MPG. 234K miles, 4L80E, less than 10K on new injectors and glows. 4.10 gears. The PO to my PO apparently towed with it as he did the snorkle delete and turbomaster. I've done the Diamond Eye 4" exhaust and a new crossover. The one thing I'm not sure about is thermostats. I know they are aftermarket (Stants?) but not the temp.
I much prefer driving this pickup, but it is rapidly getting to the point where I can't afford the fuel. The most fuel efficient car I have is a 1988 Crown Vic with the 5.0 motor, at 17-22MPG, and it handles like a boat. My next favorite rig after my 94 6.5 is my 1971 Toyota FJ40 Landcruiser, but it has a cracked head and no funds to fix it or insure it. And it doesn't get much different fuel mileage than the 94 6.5.

Don

 

[pitsingerk]

Did some diggin on Summit Racing and Randy's Ring and Pinion, it looks like my options are 3:42 and 3:73. The 3:42 gears are damn expensive. I'm not sure if dropping 200rpm by going to 3.73 would make a difference in the mpg or not.

 

[great white]

I'm going to be watching this thread closely. I'm currently getting 13-14 MPG. 234K miles, 4L80E, less than 10K on new injectors and glows. 4.10 gears. The PO to my PO apparently towed with it as he did the snorkle delete and turbomaster. I've done the Diamond Eye 4" exhaust and a new crossover. The one thing I'm not sure about is thermostats. I know they are aftermarket (Stants?) but not the temp.
I much prefer driving this pickup, but it is rapidly getting to the point where I can't afford the fuel. The most fuel efficient car I have is a 1988 Crown Vic with the 5.0 motor, at 17-22MPG, and it handles like a boat. My next favorite rig after my 94 6.5 is my 1971 Toyota FJ40 Landcruiser, but it has a cracked head and no funds to fix it or insure it. And it doesn't get much different fuel mileage than the 94 6.5.

Don

While it may not be a fun choice, you could probably sell the fj40 for decent cash (if it's in good shape other than the head) and pick up an older 4 banger econobox.

Other than that, the 6.5 is never going to really give you more than about 17-18 mpg on the best of days.

the 20-21 mpg claims are all highway and I would think highly suspect in accuracy.

The average is more likely somewhere between 14-16 mpg....

 

[ak diesel driver]

while the higher mileage is certainly all highway I knew a few people with older burbs w 6.2s that got in the high 20s on road trips

 

[DieselSlug]

When i get a 195 stat and the new turbo on im hope-ing for a little over 20 on the highway. Might happen, might not. Ive got a 4 cyl jeep wrangler that gets a solid 20 so it doesnt hurt as bad as it used too.

 

[GM Guy]

Here are mpg enhancing ideas gleaned from my experience and theories (the ones that most of you wont like, as most of you want big rubber and no rake! ) and the rest are what I have learned over the years from the fine members of this forum.

1) support our own resident oil geek, Wrecker, and he will hook you up with amsoil for a good price. synthetic oil will help on mpg, longevity, and durability, so the only downside is cost, and he makes synthetics affordable.

2) find an airdam, junkyard, LMC truck, etc. I believe GM sells them for (last check 2 years ago) 55, 57 bucks. this will divert the air around the truck, rather than under it. plus, there is some debate whether or not this will help your cooling system out, as it supposedly lowers the under vehicle air pressure, encouraging more airflow through the engine bay.

3) lowest rolling resistance rubber possible, and light rims. this is where you find a local wheel retailer that buys the new takeoff stuff from conversion companies and dealers that put big rubber on. you then buy the OEM alloys found on 2500HD GM trucks with the wimpy highway tread bridgestone 245/75R16s.

4) keep, or return to stock suspension height. this is the most aerodynamic, but in somes opinion, the worst looking.

5) hot factory t-stats: 195 degrees!

6) mandrel bent 4 inch exhaust (with the high velocity 3 inch DP) and mandrel bent crossover. mandrel bends are smooth, so this will allow better flow than a straight piped factory system

7) Fresh rebuilt injectors, I dont know what kind of workload he can handle, but bk95td is geared up for rebuilding these.

8) 3.42s (if funds allow, and it is alot of highway travel) this will lower your engine RPMs closer to the desired 1800-1900 RPM, supposedly the best RPM range for MPG

9) ATT better mpg, lower temps (IAT and EGT) everyone on this forum who has one seems to love it. it is also known the GM series of turbos are quite restrictive, GM8 being the least, so if your funds only allow used, go with a GM8, but the ATT will get you the biggest jump.

10) personal driving and operating characteristics: keep a light foot, a/c off as much as possible, windows up, rolling stops (if you can get away with it with the local P/D) slower speeds, etc.

11) engine timing, programming. I will stop here and let someone else explain it right, but fine tuning the powertrain via electronics will help you with mpg and power.

 

[GM Guy]

as for the possibility of over 20 mpg? entirely possible. I have hit 23 with the 96, and averaged 18-21. it is of course 5spd 2wd 3.73s.

dad has a few buddies that have or had a 6.2L, and the one claimed one leg got 33 with a tailwind. most of them said 25 wasnt out of reach on the highway.

 

[3500GMC]

Here's thread along these lines. Had some good comments in it.

http://www.thetruckstop.us/forum/showthread.php?21360-Actual-honest-real-world-MPG-from-your-6.5

 

[GM Guy]

I was looking for that thread! damn search..

 

[THEFERMANATOR]

Sounds liek your on the right track. I know my BURB when it was a 6.5 got about 17 at 70, but dropping down to 68 got me about 18.5MPG. Also running a good stock height tire(245/75/16's) will help ALOT. I had 265/75/16's and basically lost 2 MPG off all around with the 6.5. New injectors are a good thing to have, and a diamond eye 4" exhaust would be beneficial. As for a gear swap, do you tow at all? If so I would think LONG and hard about this one before making a decision. 3.42 gears will knock your towing ability down a good bit from 4.10's, not to mention if you want a quiet set of gears AAM's are the ONLY ones to run. A front and rear set with bearings and install kits will set you back about $800-900(this is about what I paid 2 years ago for mine), then install if you don't have the tools to do it can cost you another $500 REALLY quick as most people don't like building up the front IFS unit. Even at $4+ a gallon you can buy ALOT of diesel for what a gear swap will cost you since you will only be looking at a 2MPG increase most likely at 70. This means you will have to run roughly 53 tanks of fuel through the BURB to offset the gear swap cost figuring $4.50 a gallon and a 2 MPG improvement. I don't know about you, but that's about 2 1/2-3 years worth the driving for me in my BURB. If it wasn't for the fact I knew teh DURAMAX would have been downright dangerous to drive with 4.10 gears, I would still have them in my BURB now(even wioth 3.42 gears it gets mighty squirly at times).

 

[WarWagon]

Your MPG is about as good as it gets without throwing a bunch of cash at it. You are doing better than me, but, I am loaded most of the time. The peak torque of the engine appears to be 2100-2200 RPM. For my tires and 4.10's this is around 62 MPH. This body style looses economy over 65 quickly and so do even the newer trucks. (My 2008 Duramax did.)

In short driving style, load, and speed play a lot in MPG. So clean out the junk you are hauling around that you don't need.

The rest of the changes need a economic study. For example going from 8.9 MPG to 10 MPG towing 560 miles a day 5 days a week pays for a $500 exhaust system in fuel savings after 6 weeks. So is the large short term investment going to pay you back soon enough?

Otherwise you should be happy with what you are getting with a comfortable large 4x4. The gassers are not doing as good, but, their fuel is costing them less.

 

[Franko914]

Here are mpg enhancing ideas gleaned from my experience and theories (the ones that most of you wont like, as most of you want big rubber and no rake! ) and the rest are what I have learned over the years from the fine members of this forum.

...<snip>...
3) lowest rolling resistance rubber possible, and light rims. this is where you find a local wheel retailer that buys the new takeoff stuff from conversion companies and dealers that put big rubber on. you then buy the OEM alloys found on 2500HD GM trucks with the wimpy highway tread bridgestone 245/75R16s.
...<snip>...

** Install the tallest/highest profile tire you can get that you can pump to 45-50 psi or above. The higher the pressure, the less tendency to "squish" the tire... the more the tire is squished, the higher the rolling friction.

The taller/larger diameter the tire, the greater the circumference which gives the net effect of lower gear ratio.

Example:

- 265x65x16 = 29.563 in. diameter, 92.875 in. circumference

- 285x75x16 = 32.831 in. diameter, 103.142 in. circumference, i.e., 11% increase in circumference

-- for 4.10 gear ratio, net is 3.69
-- for 3.73 gear ratio, net is 3.36
-- for 3.42 gear ratio, net is 3.08

The speedo must be recalibrated. RPMs will drop if driven at the same reference speeds, i.e., hypothetically, 2100 RPM at 70 mph will drop to 1891 at recalibrated 70 mph.

** Install an HHO generator (perfect for diesels, turbo or NA because there is no O2 sensor to contend with), the net effect being a more efficient burn of the fuel requiring less fuel as before to perform the same work.

** Adjust the suspension to impart a "rake" on the vehicle's profile: lower in front, higher in the back. This, apparently, improves the vehicle's aerodynamic performance at higher speeds.

** Remove rear air spoilers, if installed, the ones that direct air to the rear windshield from above or from the sides as they are very bad for aerodynamic profile, and front external sun visor for the same reason.

** If you do a lot of stop/start or city driving, definitely replace steel rims with lighter alloy wheels, otherwise, the heavier steels will help (very slightly) for mostly highway driving due to the laws of physics governing conservation of momentum.

** Pump tires with helium... travel in daylight as air is less dense... select routes that only go downhill... only go westward to counteract the earth's rotation... only go eastward if above 30,000 feet to take advantage of jet stream (just kidding...)

Our 81 2WD 6.2NA sub easily got 26 mpg on the highway at 65 mph (drove from Missouri to NY: with top-mount rear air spoiler, got 24-25 mpg; without rear air spoiler, got 26+ mpg). With a 40 gallon tank, range was 1,000 miles.

Our 98 4WD 6.5TD Tahoe gets 20-21+ mpg on highway (NY to Florida and back). Got new high profile tires but unable to obtain mileage as head gasket needs replacement... soon, I hope...

 

[handcannon]

While it may not be a fun choice, you could probably sell the fj40 for decent cash (if it's in good shape other than the head) and pick up an older 4 banger econobox.

Other than that, the 6.5 is never going to really give you more than about 17-18 mpg on the best of days.

the 20-21 mpg claims are all highway and I would think highly suspect in accuracy.

The average is more likely somewhere between 14-16 mpg....

BJ--Sell my FJ40? My hunting rig? My Toy? You'll have to pry it out of my cold dead hands. Seriously, I understand what you're saying, where you're coming from. I have something else to do first. I have a 93 F250 4X4, extra cab, color matched tall glass canopy, air bags, most all the interior bells and whistles, good looking and good running that I'm about ready to put on craigslist. I may have to use it as a trade-in though since it has the 460 in it. Between being very hard on gas and my back it hasn't hardly been driven in the past three years so it's got to go, especially since the 94 6.5 has proven to be reliable, and easy on my back. The Ford is actually a better workhorse than the 6.5. I've had the Ford loaded with a cord of semi-green oak and madrone firewood and towing a trailer with a cord of the same firewood without it hardly breaking into a sweat. But that will be no more because of my back.

I was initially hoping for a bit better MPG out of the 6.5, but even with 4X4 and the turbomaster and the 4.10's it's still way better than the Ford 460. I would consider changing to 3.73's if it can be proven to me that I could still tow a 26' TT without too much loss of ability over the 4.10's.

I have an 83 half ton pickup with the 6.2 that I'm wanting to eventually swap into the FJ40. The 6.2, a later model 700R4 beefed up a little, and swapping from 4.11 to 3.73's and using 35's for tires I'm hoping will put the FJ40 into the mid to upper teens for MPG. The little bit I drove the 83 I was getting around 17 MPG with it. I bought the 83 primarily to use the bed for a trailer. If I can sell the Ford and an extra travel trailer we have for some cash then maybe I can afford my dream Toy. In the meantime, I have a replacement head for the 40. I just need to scrape up a couple hundred to have the head shaved and the valves touched up.

As for MPG claims, some vehicles seem to do better than others for unexplicable reasons, even though identical. We have two identical Astro vans, a 97 and a 98, that were built only a few months apart in 97. The 98 has always done about 2-3 MPG better than the 97 on long runs. Go figure. I always take the high MPG claims with a grain of salt, but I do know that there are a few rigs that will do that for some unknown reason.

Don

 

[vaicase]

yes the 6.5 with 4.10 gears and being a 4x4. will get you about 13.5 stop and go. to about 16.2 is the best i got once. ive had the truck for almost a year and a half. power service does not help. 2cycle oil does not help. it does quiet the engine though. after market exhaust and air filter . no help. at least not for me. even summer fuel here in kansas. no change. no miracles out there. dont beleive the snake oil salesman. dont drive a diesel unless you have too. and slow down. that helps a lot. thanks for your intrest.

 

[tanman_2006]

I am considering buying 2 82 6.2 liter trucks (going to look and possibly buy 2mro afternoon), hoping for near 25 mpg but no less than 22. I am going to get the 2 trucks for 600 total and use parts from the 2 to make one solid truck that still needs restored, but that can be an on going project. Seems like a worth while investment with the fuel price trends.

I will be posting pics of the trucks 2mro evening on my thread in the 6.2 section.

My 95 Z71 w/ 3.73's gets 19 CONSISTANTLY at 70 mph. It has gotten 22 at the same speeds going across the flat lands of OK Panhandle and West KS. I can break 20 if I stay at 62 ~2000 rpm and keep my foot out of it in economy mode and using all the good driving techniques given.