2500HD Pickup Truck Efficiency Project

[aardvarcus]

All,
First of all, I appreciate everyone’s willingness to share their knowledge on this site. I thought I would share a project I have and hope to get some constructive feedback. Having read most of the truck related posts on this site, I made a background section to fill in most of the blanks many people leave out. Those wishing to skip to the heart of the matter can go down to the real discussion section below.

----Background----
First off, my daily driver on my 100+ mile round trip daily commute is a Toyota Celica (36-38 MPG). I also have worked construction in the past and am presently building my own super insulated house. My daily driver from home to the construction site is a 1991 Chevy K2500 Light Duty (6 lug ¾ Ton). This truck “works” but is falling apart and I am constantly fixing things on it (Transmission Issues, 4WD issues, Etcetera). I needed a heavier duty truck to do some of the more demanding construction related tasks as well as a truck I trust to drive more than 30 minutes from the house. To this end I purchased a 2001 Chevy 2500HD 4x4 extended cab with the 8.1L Gas Burner and the Allison Automatic Transmission. Its present use is hauling heavy loads I don’t trust the other truck with, hauling lighter loads that go a distance from the house I don’t trust the other truck with, and as the only four door vehicle we have hauling 3-5 people when necessary. I know the last two uses are a waste of the trucks capacity and already have plans to address that.
To answer some of the initial feedback I already know I will get:
You should have gotten a Diesel: Probably but couldn’t find a decent one in the budget, and yes I am going to pay for it in the long run. May do a Diesel swap if the engine goes kaput.
You should have gotten a Manual: I desperately wanted one and searched for three months for one that wasn’t way overpriced or beat to death and I was going to keep searching, but I could not pass up the deal I got on this truck. May do a manual swap if the transmission goes kaput.
You should buy a four door car so you don’t have to drive that dumb truck around when you have people you need to take somewhere: I am planning on getting my wife a smaller four door car after the house is done for this very reason.
You should have gotten a half ton/midsize: After the house is built, I am planning on selling the anemic K2500 and buying a half ton or midsize for most of my daily use, but I still need the heavy duty truck for harder hauling (3000lbs+) and towing (10000lbs+) and for “abusive” use (pulling logs through woods, etcetera).

----Real Discussion---
So basically I am going to have this truck for quite a while (unlike my other vehicles) so I would like to begin to squeeze the best economy I can out of this behemoth, though I hope in the future to be using it less and less. I have been averaging 11 mpg with a mix of construction use and town and back hardware store trips. On mainly highway driving with light loads I have been getting closer to 14 mpg. Honestly it is getting very similar to my k2500 which only has the 5.7 in it.
My goal is to get those numbers to 14-15 mixed use and 18-19 highway long term. I am planning to do this though a variety of modifications done slowly over time; however I can’t do anything to make it less of a 1 Ton truck. After tuning the engine, I have plans to make some aerodynamic changes to the body, however at the downside of adding weight. The truck is already very heavy and I feel that the weight aspect is already a lost cause. Anything I add to the truck needs to be able to withstand the rigors of its use, and while I have no intention of going crazy and welding ¼” plate to it, any body modifications would probably involve thin sheet metal over a tube frame, which will make it heavier. Here is what is in the works:

Completed Mods-
Changing all fluids to synthetic. (Engine, Transmission, Transfer Case, Differentials)
255/85/16 All Terrain Tires (Not the most fuel efficient, but for the ground clearance and traction I need a better fuel economy choice than 285/75/16 Re addressing below)

Currently underway Mods-
Replacing Spark Plugs and Wires
Tuning Engine/Transmission to increase Efficiency

Planned Near Term Mods-
Hard Folding Bed Cover
Additional Street Tires for better on-road economy (235/80/17 Michelin Street Tires- Green X, mounted on extra set of rims)
Transition Filler Pieces (Cab to Bed, Hood to Windshield, etcetera- Probably Foam)
New Shocks (Not so much for efficiency)

Mid Term Mods-
Belly Pan (Improve airflow under truck- Must Have Decent Metal Frame, will do either thin sheet metal or coroplast over metal frame for actual Pan)
Step Bars Incorporated into Belly Pan Frame (I pulled off the non-aerodynamic step bars, and my wife didn't exactly appreciate it.)
Aerodynamic Tire Transitions
Rear Suspension Drop (Due to body rake can lower back a full 3” with only ½” loss in ground clearance)

Long Term Mods Under Consideration-
“Fastback” Cab to Bed Wing Transition (Like the first 1/3 of a full sloping aero shell, to complement Bed cover similar to wing that Texas Tech used)
New Heavy Duty Front Bumper/ Clip (Incorporate entire front clip into new bumper, aerodynamically shaped, shuttered front grill that partially closes at high speeds) (Will add significant weight)
New Heavy Duty Rear Bumper (Smooth transition from belly pan out, will also add significant weight)
Electric Fans
Air Bag Raising/Lowering System (Probably too complicated to do correctly with no loss in capacity)

You all are the experts, so feel free to critique my planned mods, offer insight, suggest mods, etcetera.

[oil pan 4]

If you are going to add a big front bumper you might just want to stick with an air dam, the belly pans are a lot of work since you are going to change the bumper anyway.
I think the idea with belly pans is to keep them as low to the ground and as parrel with the ground as possible. It looks like I am going to build a custom bumper to house the intercooler for my diesel so I will kind of be doing the air dam thing too.
Depending on what kind of towing you do you may not want electric fans. The duramaxes went to electric clutch in the early 2000s. That may be your best bet for cooling.
The problem with thermal clutchs is they dont seem to ever really fully disengauge. I picked up 2.2mpg when I did my belt to electric fan swap back in 2006.

I may add air bags too. All ready have compressed air on the truck so might as well.

That transmission isn't going to die unless you really try to kill it.

You may want to figure out what gears you have in the differentials and think about swapping them if you really dont need them.
I use to get by with 3.08 gears towing 6,000lb with no hills.
Since I haven't towed any where near that much since 2007 I am thinking about building up a rearend with 2.73 gears now that I have it turboed.

[aardvarcus]

Thank you for your thoughtful reply.

My plan for the bumper is not to go any lower than where the stock one is right now, so not really an air dam to the ground type bumper, just a smoother flowing one. I still need to maintain decent ground clearance. My thoughts on the bumper are just to smoothly direct the air flow above, beside, and under the truck. Right now my front in has huge panel gaps(1/2" min to 2"+, no joke) that can't be aerodynamic at all. The front is way too open, the truck needs less.
My Belly Pan would be mounted at the height of the lowest cross member, which is 1.5" below the frame. That way I don't give up ground clearance, my lowest point is still the lowest point; just now that height is everywhere.

I had thought the Duramaxes were on thermal fan clutches, but I will certainly look into that. That would probably be a better idea than an E fan if I can find something that will work. Might have to modify something, a clutch is a clutch. I am going to get my programmer to engage the electric pin, so I can wire that up to run a clutch.

I want to get air on the truck for other reasons as well, once I get the bed cover I will probably pull the trigger on that. It is just nice to have.

Yeah, the Allison is basically the only reason I relented and got an automatic, I have heard they are bulletproof. Mine is an older one, and after I put the correct Dextron 3 fluid in it (Transynd) it really shifts nice and smooth. Previous owner must have put Dex 6 or some cheap Dex 3 in it, because it was clean and working, but it just wasn't shifting right. I hope no long term damage was done.

Yeah, I had thought about the gear swap and it just slipped my mind when I typed this up. I think right now I have 3.73 or 4.10 in it, but first gear on the Ally is so low I could go a lot lower no problem. If I had to do an extreme task there is always 4-Lo.

[freebeard]

If you make it a tail-dragger mid-term you might want to move the airbags up from long-term. So you can, y'know, put a load in it. I wonder if a forward rake means less need for a belly-pan.

Make your air dam out of hangar door seal:
Aircraft Hanger Door Brush Seal | Precision Brush

If you use a 6" brush put 3" of lawn edging behind it for backup.

If I had a contractor's truck, I'd want a 110VAC outlet right below the right-hand taillight.

[aardvarcus]

Thank you for your reply.

Good point about the overload air bags. Right now the rear suspension has the potential for 7” of travel, but the truck has these massive 4” rubber bump stops, netting only 3” of travel. I thought however much I dropped the rear I would trim the bump stops as well. That way I would have the exact same cargo capacity until I hit the stops. It would be better for aero for the truck to sit level under load as well. So with overload air bags if I dropped it to level empty, and it sagged several inches under load, I could air it back up to level. The bed is so high that a 3” rear drop would bring it probably 4” further down, making it more useful.

When I put the air bags under long term, I was referring to the “make the whole truck go up and down like a lowrider” airbag systems, which would work in series with the current suspension. For the size of this truck, the ground clearance is pretty pitiful, but the center of gravity is very high. Makes me a tad uncomfortable on the turns, though granted it needs new sway bar bushings and shocks. I would love to drop the whole truck (from stock -2” front -5” rear) for onroad, and then when offroad air up the bags to raise the truck back up (from stock +2” front, 0” Rear). Biggest issue is the bump steer in the IFS would make me significantly lose my alignment when raised up, and my front drive shafts would constantly be operating at an angle, and I am not confident in the durability of said system.

Very good point about the hanger door seal, that wouldn’t really count as any loss in ground clearance. I did not realize they made brushes up to 6.” That is a new material in my arsenal, and would certainly come in handy smoothing flow around tires.

One reason I wanted the belly pan would be to smoothly transition that out to some “step bars” by making the belly pan stick out a few inches past the bottom of the truck. It would also give me a good location to mount tire fairings. It would also provide minor protection to the underside of the truck, though it wouldn’t really be thick enough to protect from anything major or it would be overly heavy.

I may try (again) to seal up the panel gaps on the current front bumper/clip as a temporary solution. I already tried with flexible rubber and pipe foam insulation, but most of them came out after just a few miles of use, and I had to remove ¾ of them because I knew they wouldn’t stay. I want to plug the gaps around the headlights, the top half of the grille (this part removable), and the 2” gap between the lower grill trim and the top of the bumper. Here is what I was considering for my second attempt. Sticking strips of thin black plastic sheeting (trash bag) into the panel gaps, and then shooting it full of expanding foam (Great Stuff Pro). When it hardened, I would remove it from the gap (plastic prevents bonding to parts), trim it and shape the front of it as necessary, and paint the front of it for protection, with it still having plastic on the sides and back. Then I would stick it back into the gaps and do something to hold it in place. This was also my idea for the cab to bed gap. The foam would allow for minor movement, but be close enough to the appropriate shape that I don’t think it would want to fall out like the pushed in foam pieces wanted to. Any thoughts on this area?

[Sporty Modder]

Just a thought , in regards to your bumpstops. Manufacturers today build the suspension to use the bumpstops as secondary springs, it is common when lowering a truck to really affect rhe handeling and ride when trimming the bumpstops. Just somethibg to keep in mind.

[Diesel_Dave]

First off, welcome to the site!

It's not that sexy, but in my opinion, the first step that you need to do is start keeping a good fuel log (if you're not already--I see you have one fill already on your fuel long on this site).

Another thing that I would consider a "must" is getting some kind on real-time fuel economy feedback. I'm guessing the stock truck doesn't have anything. Most folks around here will attest to the fact that driving mods will typically buy you more fuel economy that vehicle mods will. Of course with an auto tranny, you'll be more limited, but I think you'll be shocked how much you can improve things with driving mods.

After you get some good record-keeping, just start making one mod at a time and you'll start seeing progress.

Good luck!

[slowmover]

Originally Posted by Diesel_Dave

First off, welcome to the site!

It's not that sexy, but in my opinion, the first step that you need to do is start keeping a good fuel log (if you're not already--I see you have one fill already on your fuel long on this site).

Another thing that I would consider a "must" is getting some kind on real-time fuel economy feedback. I'm guessing the stock truck doesn't have anything. Most folks around here will attest to the fact that driving mods will typically buy you more fuel economy that vehicle mods will. Of course with an auto tranny, you'll be more limited, but I think you'll be shocked how much you can improve things with driving mods.

After you get some good record-keeping, just start making one mod at a time and you'll start seeing progress.

Good luck!

Nothing less than all gallons, all miles is acceptable, IMO, when it comes to record keeping. One needs to know average mpg and to correlate against average mph (etc) to, in the end, chart the percentage decrease in fuel burn for the work (as one way of making money by understanding the numbers generated by vehicle use).

I see that this is not the daily driver. That gives one the elbow room to trip plan every moment of engine-on time. Routing for best use of fuel, etc. Higher mpg is a nice achievement, but lowest fuel burn for work accomplished means more with a truck (as conditions may be different every time: load, temps, way & end points, etc).

The V8-496 is popular with RV'ers, not just contractors, so there will always be a buyer out there for an extra-clean vehicle that shows well (steam clean & paint chassis where applicable; detail interior, etc) so don't forget that someone may want to buy it off of you at any given stop (and that might help fund the exact vehicle you want in the future). It's a good place to start (after weighing vehicle on a CAT Scale with driver & full fuel when otherwise empty). KENWORTH and CUMMINS both make points about alignment, brake drag, and steering wander for mpg purposes. Assume nothing is right, and make them perfect. These are the places to start, IMO. You'll make more "money" fixing any steering wander than with any other repair/change/modification.

Next would be electric heaters for the various fluids (as used in northerly climes) as reduction of warm-up time/distance is vital with big motors & heavy vehicles for any climate & season. (Threads around here to read).

Aero is great, but focus on the "regional metro" mechanical stuff first, IMO.

Used as a business tool -- no "engine-on" time that is not already pre-planned in all respects -- and with proper records one can reduce the fuel cost per mile of operation. Cents-per-mile is the calculation one needs to find and understand (AAA plus EDMUNDS are beginnings) as fuel cost is only one entry among many others. The first step in this is in deciding how long will keep the vehicle, and over how many miles. No work vehicle (that either earns income or offsets income) can be put into perspective without a decent guess at time & distance. One needs records to do any meaningful gains (tools of analysis).

My fuel cost is 15-cpm solo, and 25-cpm towing, but the "real" CPM is nearer 50-cpm when all is taken into consideration. While my life has changed in the years since I bought it, the overall high mpg kept it relatively cheap to own (no repairs, either, beyond paltry expenses) and as I am now an "RV full-timer" it is more accurately understood as being part of my home, not just as personal transportation (so energy consumption: electric, propane, diesel are all calculable for budgetary reasons). Example: I allow for a certain amount of "idle time" due to the climate here (hot/humid) and look to keep my average mph at/above 27-mph which keeps my overall fuel consumption within bounds. (And "my home" will change in all operating respects at some point: climate, terrain, use, etc). The balance of energy inputs will change given job, locale, etc. The vehicle is not separate (and the awards go to those who do not need a mortgage to include garages, parking space, etc).

Work vehicles are about predictability. Being able to predict fuel burn accurately is the soul of use for a single operator. Here is an example.

(And pics are always nice!)

.

[oil pan 4]

Originally Posted by freebeard

If I had a contractor's truck, I'd want a 110VAC outlet right below the right-hand taillight.

I picked up some unnamed heavy duty rear step bumper for my truck form the junk yard for $80, my old one was rusted and dented. I plan on adding a pair of outlets back there to be powered by an inverter. I may add a male prong inlet plug to make it easy to power up the block heaters.
It would be nice to have.

[aardvarcus]

Thank you for your helpful replies. Yes, I NEED to get some instrumentation, probably a ScanGauge, and do a better job on the fuel log for the green truck. I do fairly good tracking on my Celica by saving receipts with mileage hand written (need to upload them, but I have the data and I track the MPGs), but sometimes I fill my truck from a work tank pump, which is un-calibrated and I don’t get a receipt. I will make a fuel log and get a pen and put them in my truck today.

I have started on my foam gap fillers, mixed results so far. I will fine tune my process and give it another go. If it works, I will get some pictures and post it up.