My journey to 40mpg with a 1ton diesel.
 

Thanks to everyone who chimed in on my truck acquisition process here - http://ecomodder.com/forum/showthrea...uck-25506.html. After doing some research about this vehicle, and what can be done with it, it doesn't seem outside the realm of possibility to eventually achieve a 40 MPG fill up (I got 24.5 on my first 157 miles under poor conditions). I'll be logging my progress here as I go along. Any advice and feedback is always welcome and appreciated.

Truck Specs:
1991dodge ram
5.9L Cummins Turbo Diesel
Std. Cab
2wd manual transmission
V250 (sweptline with 1 ton suspension)

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Planned mods:
Kill switch on shifter
Upper/lower grill block
Engine blanket
Timing advance
Raise tire psi (80? *max side wall)
Under belly pan
Electric fan
Custom aero cap
Any others if possible

This project has a lot of merit. My truck is fairly similar.

Quick question: Stick or automatic? Just on the face of it a stick is good for a 2 MPG gain. An automatic pretty much forecloses engine-off operation unless you can repair automatics economically.

Tires: Get E-rated tires a size smaller than what you have. I get by just fine on 225-75x16s. I air them up to 100 psi. Lacking any accurately tabulated RR values I default to OEM tires.

Gearing: Very important and huge opportunity for you. Your Cummins (like my IH) has vast low-end torque. You can actually operate at much lower RPMs than you think. I operate at 1325 RPM @ 70 MPH and 1050 RPM @55 RPM and can run as low as 700 RPM around town. I use a double overdrive (ZF6+ GV) and a no-longer-available 3.08 R&P set. By reducing engine RPM at any given road speed you reduce the engine frictional HP proportionately. It is a big deal. At 2000 HP my IH engines frictional power is about 10 HP but it drops by more than 40% at 1300 HP. When you are running at the ragged edge of a "lug" you've got it just right - in the most efficient place on the BSFC-RPM map.

Aerocap: Great idea. There are a number of threads on the ecomodder forums of various options for you. I had a crude aerocap and it was good for a 3 MPG improvement over an open bed and 1.5 MPG over a flat tonneau. Visibility and utility are issues - hence the diversity. Look at aerohead's truck. Its the slickest I've seen. He gets great MPG without any mechanical mods.

Bellypan: Should help but I've never tried it. Same with grille block.

Timing advance: That helps. When it won't start in the winter back it off and that's where you want to be. If you ever want to run propane or CNG back it down to the stock advance. Too much advance + gas fuel = thrown rods.

Engine blanket: Never tried that but I use a 203 degree stat and Evans coolant. If I could find a hotter stat, I'd use it. The Evans doesn't boil (at atmospheric pressure) til over 400 degrees. Hotter coolant makes the engine tighter and more mechanically efficient. Hotter coolant transfers more heat to the atmosphere and your electric fans wouldn't need to run as much. Caution: Hotter stat leads to hotter supply air from your heater and defroster. Mine roasts my fingers on high-dash heat and cracked my windshield in icing conditions where I had to run the defroster real hard.


Please do the ecomodder and pickup truck communities a favor: Don't make your claims based on driving 20 MPH below the posted limit. There is a substantial set of Cummins guys who claim high MPG while driving 40 MPH. That is phoney because nobody drives that way. Determine your MPG over a considerable distance. Any knucklehead can coax high instantaneous MPG on the ScanGuage going slow downhill with a tailwind in perfect weather.

I use a set routine 35% Interstate (70 MPH) 40% state roads (55 MPH) and the rest urban/suburban (running along with traffic) and use a minimum of four fill-ups to to average out the error in determining fill level.

While you are getting other things together, hone whatever hypermiling you feel comfortable with (I'm Sir Coastalot with my stick shift and heavy truck but other than trying to time lights, not much else) and do a rigorous baseline. Then do some mods and run the same routine again.

Get a more modern turbocharger, maybe add a second one, straight pipe, intercooler if you don't have one.
Do the belt driven fan delete first.

I think that is a way cool project. 3.08 gears would be amazing.

I would suggest you start off with the simple things, to keep things cheap, easy and get you a little extra mileage while you are getting familiar with some hypermiling techniques.

Max sidewall in your tires: Free, 5 mins.
Antenna Delete/Relocate: Free, an hour or 2.
Mirror Delete/Interior Mirrors: Free-a few bucks, an hour tops.
Partial/Full Grill Block: Free-a few bucks, an hour - a few days depending on complexity.

Those small and quick upgrades should net you a few mpg and not take long at all to do. It would be a good start and since they are so cheap and easy, there are no excuses for procrastination (my biggest problem).

After you have done those, you can move on to the more complex and time consuming mods (belly pan, aero-cap, wheel skirts, air dam, etc.)

Big Dave:

It's a manual trans (I've been doing a little PNG and allot of eoc with my manual 1.3l ford festiva already so I feel like that will transfer well over to the truck) I agree that its better to avoid minimum speeds on the highway but I do like to go 55-60 when I have time.

I have quite good access to tires so getting more ideal ones won't be an issue.

I've never done any kind of gearing swap so this will probably be a long term goal.

I have a plan in my head for the aerocap design and it will include a lexan window and a hatch style opening system.


Oil pan:
I love doing engine mods but am limited in my experience. I need to make friends with a good diesel mechanic as I'm much more of a hands on learner. Reading the threads is helping learn what I want to do, but I don't feel that much closer to being able to do it myself.

UFO:
Thanks. And I agree that ideal gearing would be a worthwhile thing to do.

Shortie:
Thanks and I agree with you about the low hanging fruit approach. But I am definitely in this for the awesome numbers (let's face it its a game to me, albeit a practical money saving one). I'll probably end up pushing the limits with what I can do mechanically and aerodynamically as well physically.

Thanks for the suggestions and support. I think the first thing on the agenda is an oil change then I'll hit the basic free mods :-)

There is a substantial set of Cummins guys who claim high MPG while driving 40 MPH

BigDave, I've seen you make this same statement on FORD forum threads. I've never come across it. Hard enough to find anyone who doesn't speed (runs 60-mph plus) or who keeps the average mpg updated. Now, if you meanAverage MPH your comment may be on track.

Trucks are a compromise. And part of that compromise is poor handling/braking. A propensity to roll-over where cars just spin out. Trucks are geared to run 55-65/mph most efficiently. And highest mpg claims are within this range. The foolishness of running a truck faster than this has no place in any discussion of performance, or from any angle. It is beyond the pale.

When I claim no less than 24-mpg at 58-mph @ 1,725-rpm that is over tens of thousands of miles. My truck spec, climate and terrain comparisons with others makes this consistent (with those others who keep records). I've also run over 1k miles in town at 23-mpg, but this was in practicing hypermiling techniques. And I've seen just above 30-mpg in a run across southernmost Louisiana on a road where the limit was 50 for many, many miles. A fluke, in any case.

If you've other sources to cite, start a thread on the topic. FORD is at the back of the pack for good reasons . . but all turbodiesel trucks have some magic to discover in re fuel efficiency. We're all friends around here, so let's not muddy the water.

The OP has his work cut out for him in establishing the best mechanical baseline. Sounds great here at the beginning (pics seem to show an unmolested truck), but at over 20-years it's time to go through it all in re systems.

I'd start by weighing it. A CTD is fairly impervious to weight changes, but getting the weights for each axle and each wheel where the truck has driver, full fuel and any permanent supplies aboard is the adjusted empty weight over vehicle manufacturer shipping weight numbers. IOW, a weight that will never go lower. Truck tire pressure is within manufacturer specs (especially FF/RR bias) and then according to load. Accurate steering and braking is not helped by overinflation, etc. Baseline, to know how it feels when it is to spec.

The underhood electrical harnesses and then dash harness would be my main concern in where to get reliability back to new. Get the service manuals, identify the harnesses and work hard to get those OEM parts. Dealers and parts stores start eliminating stuff for 15-yr old vehicles and they then become incredibly difficult to find (at a similar level of quality). It might cost $$$, but every penny will be earned back.

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I'd love to see someone do the template overlay on this body style. I've got an 87 longbed, but I can't get it to upload a pic.

You can put a number of holset turbochargers on that cummins with nothing but off the shelf parts and adaptors.
First you have the turbos inlet, most holsets use 4''.
Most holsets use the T3 exhaust manifold flange, you exhaust manifold will work with most of holsets. Some HX40 turbos use the T4 flange.
Most holsets use a 3'' down pipe flange there are some 4'' and a 3.5''.

Any good advice for someone wanting to learn this kind of thing hands on?

Let's face it ecomodders are a very small subset of the hot rod world.

The TurboDiesel Registry used to have a loudmouth who made exorbitant claims of MPG but he admitted he never drove over 40 MPH at any time. I tried to interest him into a road trip and put the performance out for all to see, but he was never interested.

With my gearing 40 MPH means 750 RPM. I wonder what kind of MPG I could get at that RPM?

Aero mods would be less effective at 40 MPH than at 55 or 70.

But I drive the superslab a lot and 40 MPH vehicle truck will have the drug-sniffing dogs on it before long. People here in Indiana might not shoot a truck going 40 MPH on the Interstate, but they might throw a chair at it.

Yeah, Ford trucks have a big problem in the MPG department. They are very solidly and sturdily built, and that translates to HEAVY. 7,800 lb curb weight. Not good for MPG. It's a good thing I live in pool-table flat Indiana.

Swapping the turbocharger is not as hard as you think. Most swaps should only require basic tools, as long as you don't try to put a holset HE351VE on there.
I would say go with an HE351CW or some type of HX40 with a T3 flange and 3'' exhaust out let (which most HX40 are anyways).
The problem with the HE351CW is that I think it might have a 3.5'' exhaust outlet on the back of the turbocharger.
If you want to use a turbo with a 3.5'' outlet talk to me first because I have the hard to find cummins 3.5'' to 4 inch elbow, a 3.5 down pipe flange, a 3.5'' V-band clamp and a 3.5'' v-band clamp adaptor.

temporary gorilla tape grill block done
 

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Off to a good start. Be sure to watch your temps closely for a while to be sure you dont overheat. I'm sure you get plenty of air from underneath the engine bay, but you never know.

So, what is next on the list? I am looking forward to seeing your progress, maybe if you get some good numbers I can convince my brother to mod his 2500HD diesel.

The next thing on the list of mods is passenger wiper delete ( it would already be done except I can't figure out how to get the darn thing off lol) and a full synthetic oil change. I'm picking up a kill switch for it today as well. After that I plan on tackling the radiator fan. After that I'll probably fashion some rear wheel skirts and a front air dam. I'm also looking to do a ram CAI to keep a balance with getting enough air to the engine and really like diesel_Dave's results there. I have an aluminum ladder rack that is gonna be my Framing for the aero cap and I'll probably do that in conjunction with the underbelly pan. I really want to do allot of engine mods but that is still just a little out of reach for me till I gain some experience. I don't want to risk ruining a perfectly well running truck. Also looking into getting a better thermostat (205degree+Evans coolant+new hoses)

OK. I'm intrigued here. You say its pretty simple and I don't doubt you. I guess it comes down to how much fe would be gained and how much would it cost to do it. I'm definitely interested though. I do want to go all out with each mod so im not overly interested in medium upgrades over what I already have. But like I said this is new territory for me and I'm learning allot every day. I'm sure I will waste some time and money in the process. My goal is to minimize it as much as possible. :-)

Yeah my gearing is really short (I can shift into 5th at 30mph without lugging the engine) how hard is it to track down the 3.08 gearing setup?

I had to remove my cardboard grill block in my slant six. I would get hot at stop lights. You may not have that problem with your diesel. I did notice an improvement in torque when I did the fan delete. I just changed back to cold air intake since I noticed it ran stronger in cooler air. I've also lighten it to under 4000 lbs with me in it. The slant is only 450 lbs though. I've got a 3.55 rear and an automatic with overdrive hooked to an old Chevy vacuum lockup switch. It will lock at idle if I have enough speed to be in 3rd.

If you start to overheat with your grill block setup, you may want to look into doing an adjustable grill block. There are a few out there. I have seen some that use springs, servo motors, cables and mine just hinges from wind speed. They all work fine, some are just a bit more involved.

I'll just cut some slits in the bottom portion until its staying where it needs to be. I don't plan on messing with adjustable grill blocks as it seems like it would be more effort than it would be worth.

On the grille block. Just closing off the upper portion to smooth flow across the hood is likely enough (the trade-off). Diesels run cool until they don't . . and the change is almost instantaneous (is how it seems). Vital to have gauge.

The wiper arms will come off with two stout flat-blade screwdrivers 90-apart and prying upwards. Hit the area underneath with a penetrant first (I wouldn't do this, though; safety trumps 1/100th mpg).

As to using EVANS in the big truck FE world a bit of consensus is that the temps the engine will run afterwards are so high the head gasket fails. IOW, if it wasn't designed for those temps, don't. On light duty trucks (as we have) the FORD guys have some success, but given the very high cost of conversion I'd look for other First Gen CTD owners who've done the conversion first.

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If you have a transmission cooler up frount there do not block that part of the grill.

What oil are you currently running in your truck? Changing to a thinner oil can help to reduce efficiency losses do to friction. Another member has reported great gains in his 3/4 ton 6.7L cummins diesel by switching to some Amsoil Series 3000 Synthetic 5W30 Heavy Duty Diesel oil.

Diesel Dave: "The biggest change recently which put me over the top was switching to some 5W-30 synthetic oil, which has bought me another ~5-10%."

Regarding your goal stated in the original post (40 MPG) I would say its doable but don't get too far ahead of yourself. Take things slowly. Do one thing at a time. Research mods before you do them so you understand the benefits and risks. Perhaps most importantly, keep good records. You're off to a good start in the mid 20s. The path to 40 is a bunch of small steps of 1 or 2 MPG (or less).

I'll agree with oilpan that a newer turbo would probably help quite a bit. I'd have to look Ito it a little more to see what your options are. One easy option might be a junkyard turbo off the common rail 5.9s (mid 2000 model years). That wouldnt be a bad option and shouldn't be too expensive. A better option might be a turbo of the industrial 5.9s of the same era. That turbo would be better suited to the lower rpms you will run. The 5.9s in the Dodge trucks spin a lot faster than the off highway engines, primarily to show a high HP rating, wheras industrial engines want lots of low end torque.

Like oilpan said, as long as you're talking all mechanical turbos, the swap is pretty easy to do.

Diesel Dave,
Funny how you show up right after I get done mentioning you. Did you get a notification saying "somebody used your name, check it out (Link)" or is it just those hairs on the back of your neck? :p

Seriously though... Dave has done a very good job with his truck and I am sure he has a lot of useful advise that can help you to accomplish your goal.

It was getting a bit on the warm side today so I opened about 10% of the grill in the middle bottom section. After that it was holding slightly warm but doing well.

If the grille block is affecting the final coolant temp (after warmed up) at all then you've overblocked it. You want the thermostat alone to determine the final temp. If it isn't you may not be doing any damage (yet), but you're playing with fire because the thermostat is wide open and you can overheat in a hurry if you're not careful.

Yeah that was my plan to make sure it didn't exceed normal operating temps. It did climb up past it though so I pulled over and cut the slits and the temp corrected itself about a quarter mile later.

Thanks again for all the advice guys. And I am trying to take it slow. Its hard for me not to get ahead of myself sometimes. I guess I should approach this as maybe a 1year project instead of a 1month project :)

I'm not sure how many miles you put on the truck, but a 40 mpg tank is 1,400 miles--so just driving a 40 mpg tank can take a month.

BTW, I have to ask a couple questions. Where do you live (climate wise) and what type of driving do you do with the truck? These things will determine what types of mods may be off-limits for you and also what types of numbers will be acheivable. I personally do mostly commuting with my truck (kind of a waste, I know). I see you have a Festiva as well--I assume that's your commuter vehicle.

Thanks for taking an interest Dave. I live in grand rapids, mi so guess we'd have fairly similar climates. My truck is for work/hauling/commuting. I do use the festiva when I don't want or need the utility of the truck. I guess I wasn't planning in taking it one mod at a time necessarily, but I can see the where there's some benefit and wisdom to a slower more well thought out and planned process. My next mod that I hope to finish tomorrow is my push button kill switch. I have the switch and wiring ready to go, so its just a matter of getting out there and doing it now :)

40mpg is a really tall order. I have a low 2wd with a crap ton of timing, and I've gotten a best of 27mpg at normal speeds. At 40mph I might be able to get some crazy mpg numbers, but I don't have time for that. Start with 30mpg and go from there.

"Aim for the moon, even if you miss, you'll land among the stars".

Don't misunderstand the title. I don't feel that this project is 40mpg or bust. It is more of a long term goal. Obviously since I haven't recorded a 2nd fill up yet. I don't even have a hard baseline established yet. All I know is that I'm gonna do everything I can that isn't beyond reasonable to get my fe where I'd like it. At this point, other than a $4 kill switch, I haven't invested anything beyond the purchase price into it ($2,500), which leaves me about a $1,500 budget. I'll find out today, when I fill up, just what I'm really up against as a baseline. I plan to take the topper off for my next tank to compare with/without that as well.

For what it's worth, it took me 14 months to go from 25 mpg to my first 40+ mpg tank.

Sounds like a best case scenario then since I have limited mechanical expertise, and I'm basically just trying copy you guys :)

Interesting that the discussion regarding getting better mileage driving at 45mph with the diesels. I've always heard keeping rpms under 1800 was best. Also learned later on my TDI that even lower is not normally damaging and even better for mileage especially when your using your engine gently increase your coasting. I have to watch the rpms to ensure my overworked cam lobes are getting enough oil, so I feel more comfortable staying above 1100 rpm even though I still have enough torque to pull at idle. I've also noticed this also applies to gas engines as well. My D150 is going along nice and easy at 45mph at just under 1800 rpms. Once you get going above that the gearing and the poor aero really start to work against you.

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So I woke up early and got this kill switch done before heading out. It was really the easiest/most pressing mod for me since I hadn't been able to eoc yet, because i bought the truck without a working engine off solenoid. So far its working like a charm and I can't wait to put one in my Festiva as well :-)

Color me jealous! Five speed, kill switch, you even still have the stock floor mat and a radio! I had a ridiculous time getting the wipers off of mine too. I still have the grill off from where I replaced the plastic wiper knuckles.

Am I right that 91 was pre-ECM? What exactly are you switching with the kills switch? Is there an electronic fuel cut off?

pre-ecm
 

Yes I do believe that the kill switch is cutting off power to the fuel sending unit, but I think maybe its actually cutting off all the electric from the battery since all my electronics are killed until I do a half click of the kill switch to bring them back along with the fuel feed. I'm not sure if this is ideal, but it sure beats having no eoc capability and just plugging the electric in with a janky old connector that the previous owner had set up when the engine off Solenoid went out.