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Old 12-17-2020, 12:02 AM   #1 (permalink)
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Big Diesel, MPG increase ideas?



Been a while since I've been on the forum. With helps of tips here I was able to pull 38-44mpg out of my 97 corolla (26 epa average if I recall correctly) and I didn't have many mods on it, just driving style and making the vehicle in good shape.

Moving onto today... I bought a 1995 F250 4x4 with the 7.3L power stroke diesel (turbo version with no waste gate) with the 5 speed stick for hauling a trailer and doing work. I know generally trucks and mpg don't go together well but I'm wondering if there's any solid ideas.


Here's the basics I already plan to do:

Max sidewall pressure on tires (or slightly above)
full sythetic engine oil
sythetic oil for trans and axles (front has manual hubs so the guts shouldn't be spinning while in 2wd)
Front air dam (less air in radiator) atleast for winter driving to keep temps up so the diesel stays happy

Truck is not lifted, and does not have wide tires, and pretty sure the tires are stock height. Currently have a topper on it which I think should help, but I just drove it home today so no base line.

I watched a video about a programmer that the gives extra power and fuel mileage, my dad has a 96 and his experience matched what the guy said too. Then the guy went a step further upgrading exhaust size to keep exhaust temps down (death to diesels) and added a propane system. He claimed a 30% mpg increase (minus how much propane he uses). I guess the theory is propane burns hot and fast and helps the diesel to have a better and more complete burn.

I also picked up a cheap parts truck that has the same engine but is a 2001 with the larger stock turbo with waste gate, and inner cooler. I plan to try to get the truck to run first before robbing parts off it.

I'm trying to keep the truck somewhat stock looking, and also keep it's function as a truck. I burn wood to heat my house, so the plan it that it will be my new wood hauler and I'm planning to buy some heavier equipment, so needed the bigger truck.

Truck only has 190k and the engine sounds nice and tight, no hard knocks like the 7.3L's tend to get with higher miles. An elderly man had it and I think the turbo might be carboned up some since it seems like the turbo takes longer than normal to spool up.

I'm kind of thinking a belly pan might be a solid option, I live in the rust belt, so it might keep some of the salt off the body. Also planning to not drive the truck often, so I'm thinking of some sort of system to keep the batteries topped up to have less load on the alt and prolong the life of the batteries.

Front tank seems to be around 15 gal and the needle moved about 1/8th tank for 100 miles, I know not accurate at all. Assuming it's close to moving to the 1/4 tank spot, that's 3.75gal or 26.6mpg. Seems too high to me but I'll have a better idea once I drive it a bit more. The trip was mild country driving, then express way 70mph (I know slow down and mpg goes up, I had my dad following, so was on his time too).

I haven't looked too much into mpg instrumentation, from what I read it's OBD1 so MPGuino might be the main option for me, not sure how well it would play with these injectors though since they are oil pressure + electronically controlled.

Anyway that propane system is quite interesting to me, knowing how much propane it goes through is a big factor though. I plan to convert some of my yard machines (riding lawn mower, generator, etc) to propane, so currently in search for a used 500-1000gal propane tank, then I can put a nursing valve in it to refill other tanks myself, and buy the propane in bulk quantities for a pretty good price. My last fill up for my tiny leased 250gal tank was $1.45/gal, if I owned the tank it would have been $1.35/gal. Propane is my backup heat, I use atleast a tank a year purely for home heating, hot water, etc.

Long post, congrats if you made it to the end of my rambling =).


Last edited by MetroMPG; 01-20-2021 at 01:09 PM.. Reason: (added pic to post)
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Old 12-17-2020, 12:10 AM   #2 (permalink)
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Tires, air dam and synthetic fluids all sound spot-on.

I'm no diesel tuner, but my reading has suggested most diesels have severely power- and economy-compromised tunes, because there's a very large tradeoff with emissions (think back to the VW TDi scandal). Tuners (as I understand) mainly adjust injector timing to get these gains. It's not something you can do easily without a dyno, but these trucks are old enough that the changes to be made are extremely well documented and you should see large improvements with a canned tune.
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Old 12-17-2020, 12:33 AM   #3 (permalink)
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Yea, most tuners are generally looking for more power. Really stock it has plenty of power for 99% of what I want to do with it, I just wanted the diesel over gas. Personally not a fan of Ford engines, IH made the 7.3L and it's a known long lasting engine with not many problems long term.

I'm sure the tuning is pretty crippled on it, the specs I see online says it should be around 450ft-lb of torque stock, the 2001 parts truck I have should be around 505ft-lbs of torque. Inner cooler and slightly larger turbo are the main differences I'm aware of. I know diesel's love turbos to be more efficient and the inner cooler is a solid increase too.

I remember one member on here was pulling something like 50mpg out of a diesel truck, I think it was a Dodge, probably a 2wd that was areo modded.

Ideally this truck should solve my problem of overloading my truck with wood, this Ford should be more than capable for most of my loads. My last truck was a 1998 Toyota T100 4x4 with the 3.4L V6 with 5 speed stick. It got around 20-22mpg when I focused on mileage. Wish Toyota would make a true 1 ton truck, my closest 2nd pick would be a 2007+ Tundra, but locally they run around $12-15k, I have $3.5k into this truck and $1.3k in the parts truck (quite on the last owner, should be a simple fix to get running). The guy with the parts trunk cranked on it enough to kill the starter, luckily the big heavy diesel starter is only $110 shipped and is an easy job to do.

Sadly there's not many people on here with bigger trucks to compare my performance vs others. So far found a couple people with some history and trying to get mpg and around 20mpg is the line they are hanging around, general public is around 15-16mpg.

I'd guess I'm probably around the 20mpg mark but won't know until I get it legal and get some miles on it. The U joint is bad on it, so had to shift at higher rpm than I'd like (~2000 rpm) to keep from having the heavy vibration. If I can get 20mpg, that will be on par with my smaller "mid" sized truck and have tons more power and and such.

I suspect I should pull some alright numbers. My dad beat on his which was a 1996 automatic, everything else the same, and with the tuner on the first stage he was getting around 15mpg beating on it, 13mpg before the tuner. Clearly that was before we got into mpg and such. He still has his truck, 100k miles and has an electronic issue with the transmission system he hasn't dedicated time to looking into. He's had it sitting for 15-20 years. I think getting the same truck might spark some motivation in him lol.
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Old 12-17-2020, 02:03 AM   #4 (permalink)
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What weather do you have? Would water injection be a possibility? (At least during summer months?)

The EPA has really cracked down on diesel tuners recently. So finding kits that change the tune for any reason can be hard unless it's an EPA approved kit.

EGR delete would help fuel mileage but increase NOx emissions. One the other hand, a water injection setup would help reduce those NOx emissions again. (Just don't let the EPA know.)

Propane is easier to get and handel and cheaper to set up, but natural gas is safer since it has a higher octane.

Since you already cut fire wood, wood gas also comes to mind.

There's also the home manufacturing of nearly free bio diesel.

The main thing that helped me get good mileage in the diesel I had was to floor it and keep the gears as high as possible without lugging the engine. Pulse and gliding helped considerably.

Last edited by Isaac Zachary; 12-17-2020 at 02:09 AM..
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Old 12-17-2020, 02:13 AM   #5 (permalink)
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I'm in Michigan, no inspections or any of that extra stuff (yet atleast). Weather is cold, at or below freezing during the day.

My dad has a tuner already, it's an old one but it's a good one. I guess it VIN locks when an engine is tuned, sounds like a way to leech more money from potential buyers. There's another tuner that's basically the same thing that's updated. These are not the ebay trick the sensors into giving false readings to the computer type of tuners, these reflash the EEPROM in the computer, no wire hacking etc, just plug in and flash.

Interesting on the pulse and gliding, I didn't even think about the load effect since I figured that was more a gas engine thing. In my corolla, for ~1 mile I tried extreme pulse and glide, something like 15mph -> 35mph then back down and the scan gauge said something like 70mpg. It wasn't something I could do long term but was fun to try out.

I'm not sure how well the diesel would do being floored though, they tend to dump excess fuel and the black smoke rolling out is unburnt fuel, aka inefficiency. There's no throttle plate in a Diesel, so I don't really understand the theory/concept behind pulse and glide with a diesel.

On the corolla test run, I was loading it to the ideal %, can't remember off hand what it was, like 70 or 80% though. It was an automatic, so there was a fine line between loading the engine enough and going too far and having it down shift.

Either case, it's an interesting idea.
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Old 12-17-2020, 02:18 AM   #6 (permalink)
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I found the other member with a diesel truck that hit 50mpg. Here's the link if anyone wanted to blast to the past. The F250 is also a 3/4 ton class truck (it hauls more than 1500lbs in the back of it, it's all marketing anymore for that figure).

https://ecomodder.com/forum/showthre...kup-21766.html
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Old 12-17-2020, 02:31 AM   #7 (permalink)
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Pulse and gliding also works in a diesel because efficiency changes with load, but this time due to combustion temps. The hotter the working fluid the more energy can be extracted from it. In an ideal engine you'd use pure oxygen and fuel in the most concentrated form possible (i.e. liquid form for both) and then burn them into a trillion degree ball of molten plasma in a cylinder.

Diesels also run leaner than stoichiometric even at full throttle (unless tuned to roll coal). Yes, you get more suit at higher loads that's partially burned fuel. But all in all you usually get maximum efficiencies at 100% load, unlike a gasoline engine that drops at too high of a load due to fuel enrichment richer than stoichiometric.

Propane or natural gas can help burn up even more fuel so you get less suit, at least in theory.
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Old 12-17-2020, 03:01 AM   #8 (permalink)
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Thanks for the theory behind the P&G on the diesel, makes sense to me.

I found a person with a similar truck as me, they have much higher geared axles though, 3.08 vs mine being either 3.55 or 3.73 (pretty sure it's 3.55 though). They have some areo mods (air dam, side skirts, and lowered 4in) and they pull ~26mpg. Based on what I've read on gear ratios and some experience, it's pretty 1:1 for the ratio difference, so 3.55 gearing is about 13.2% lower geared, so their mpg with my gearing should be around 22.57mpg, so I think an unmodded truck getting around 20mpg seems about spot on.

I never quite figured out why my corolla got such good mpg, I didn't do anything super crazy with it. When I was hitting near 45mpg tanks, it was 45mph back roads, ~1hr drive, and half engine bay belly pan and about 1/4 air block at the front of the car, max side wall pressure on tires and drive it for mpg (high load take off, cruse highest gear lowest rpm effectively). The car liked to go into full advanced timing, 39 degrees if I remember right, but if I could just barely touch the gas just right I could get it to pull back the timing to somewhere around 26 degrees and the mpg jumped way up. That car was a bit of an odd duck, it's sitting with 305k miles now, Michigan rust got to it, hoping to have it fixed for this winter.

Based on a couple sources, the effect of adding propane is similar to nitrous. Both help the diesel get burnt more completely and both added together gives a tiny bit of gain from the extra fuel (propane). The catcher is, nitrous only works basically at full throttle while propane hits a nice wide range of rpm.

I never really been into diesels much in the past, but it seems that they can really pull some impressive mpg numbers even in large vehicles. 20-22mpg Is kind of my target, if I can pull 25mpg+ I'd be quite impressed and probably be kicking myself for not doing the truck upgrade sooner lol.
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Old 12-17-2020, 03:06 AM   #9 (permalink)
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Is the parts truck 4wd as well?
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Old 12-17-2020, 03:08 AM   #10 (permalink)
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Just be careful with propane. Propane can knock and cause engine damage. The key would be to make sure you don't use too much.

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