Big Diesel, MPG increase ideas?

[Isaac Zachary]

Originally Posted by ps2fixer

That doesn't match my experience driving with no cooling fan at all. Ideling will overheat the engine, moving slowly like 15-25mph it stabilizes fairly well, and 35mph+ it cools and never gets any hotter than with the fan. I'd dare to say you have a dirty radiator, restricted coolant flow, or the vehicle is of a poor design.

You sound like you're talking about flat ground. Cruising along at highway speeds on flat ground only needs about 20hp or about 15kW of power in most vehicles, give or take. At 15% efficiency that's outputting only about 85kW of heat, half of which goes out the exhaust, not the radiator. But that same engine will have to produce 5 to 10 times that power, and therefor 5 to 10 times the heat, going up a steep mountain pass. That could be some 400kW of heat output or more!

Every vehicle design is different. Granted the engine on my car didn't immediately overheat going up that 7% grade at full throttle going as fast as the car possibly could (1984 VW Golf diesel), but the gauge did slowly keep getting higher and higher until it was nearly at the red. The cooling system was perfectly fine with new pump, thermostat and coolant and actually I had more problems with the engine running too cool than running too hot.

Many of the commercial vehicle's I've driven will audibly engage the fan on hill climbs too even going as fast as 45mph or better.

Of course keep in mind too that the fan is aided by the movement of the vehicle. So you get even more air flow when the fan engages.

I find the statement of a Nascar vehicle needing a radiator the size of a beer can very hard to believe although reading THIS it looks like they do reduce the size of the grill for aerodynamics reasons but end up with coolant running temperatures of 280°-290°F (and oil temps of 320°-330°) as a result!

[ps2fixer]

Flat ground or going vertical, wind speed and surface area doesn't change. I wasn't looking at the thermo transfers, purely the wind speeds. The wind on it's own exceeds the speed a fan can move it. Of course a spinning fan vs a stopped fan, the spinning fan will have less drag/resistance, so maybe that's why the fan kicks on?

Yea, I don't take too much from the racing world since it's a different environment. On my corolla I blocked off the upper grill, and around 70% of the lower grill. The opening for air was around 6in wide and 4in tall and never had overheating issues.

If the fan was so critical for normal operation, then blocking off the grill would cause more overheating problems even with the fan. Of course blocking it off completely would cause overheating problems, and that would be quite a test to try out. Block the front completely (as best as possible) and run on cooling of only the fan to see if at express way speeds (75mph) the vehicle runs hotter or not.

Generally speaking, wind resistance is a greater force to overcome than a hill, of course combine both and it takes even more power. I haven't done the math to see how much extra power is required to continue at the same speed up a given slope but 5-10 times seems a bit excessive. You can't measure the power based on how much throttle you give it, engine rpm is a major factor in HP output, atleast as I understand it. A lot likely depends on total weight of the vehicle too since a light vehicle has a much larger % of load being purely wind resistance while a semi truck has a lot of rolling resistance and the raw fight against gravity on a hill. I wouldn't be surprised if a semi needed 5-10 times the power to go up a steep hill and keep the same speed vs flat ground.

Anyway, hopefully I'm not coming off as trying to fight you or anything. Just some of the statements go against my experience. It would be interesting to read more up on the subject that keeps things in check, like using the math for the physics and accounting for the hill vs flat ground etc.

I did read that the 7.3l trucks temp gauge has an extra resistor inline with the sensor so it reads colder than normal. From what I read people speculate that with a big load it would push into the hot area and could spook some owners so they opted to lower the reading on the gauge. On mine, it runs about 1/4 the gauge lower than the middle "normal" spot and people say the gas trucks run dead center.

[cRiPpLe_rOoStEr]

Originally Posted by Isaac Zachary

Cruising along at highway speeds on flat ground only needs about 20hp or about 15kW of power in most vehicles, give or take.

It's usually true for compact cars, with trucks being a completely different animal. It's also worth to remind the torque output at such power figures may also vary, just like the engine speed. Otherwise it would be possible to simply put a horizontal-single Yanmar stationary engine even into a full-size truck and call it a day

[Isaac Zachary]

Originally Posted by ps2fixer

Flat ground or going vertical, wind speed and surface area doesn't change. I wasn't looking at the thermo transfers, purely the wind speeds. The wind on it's own exceeds the speed a fan can move it. Of course a spinning fan vs a stopped fan, the spinning fan will have less drag/resistance, so maybe that's why the fan kicks on?

Yea, I don't take too much from the racing world since it's a different environment. On my corolla I blocked off the upper grill, and around 70% of the lower grill. The opening for air was around 6in wide and 4in tall and never had overheating issues.

If the fan was so critical for normal operation, then blocking off the grill would cause more overheating problems even with the fan. Of course blocking it off completely would cause overheating problems, and that would be quite a test to try out. Block the front completely (as best as possible) and run on cooling of only the fan to see if at express way speeds (75mph) the vehicle runs hotter or not.

Generally speaking, wind resistance is a greater force to overcome than a hill, of course combine both and it takes even more power. I haven't done the math to see how much extra power is required to continue at the same speed up a given slope but 5-10 times seems a bit excessive. You can't measure the power based on how much throttle you give it, engine rpm is a major factor in HP output, atleast as I understand it. A lot likely depends on total weight of the vehicle too since a light vehicle has a much larger % of load being purely wind resistance while a semi truck has a lot of rolling resistance and the raw fight against gravity on a hill. I wouldn't be surprised if a semi needed 5-10 times the power to go up a steep hill and keep the same speed vs flat ground.

Anyway, hopefully I'm not coming off as trying to fight you or anything. Just some of the statements go against my experience. It would be interesting to read more up on the subject that keeps things in check, like using the math for the physics and accounting for the hill vs flat ground etc.

I did read that the 7.3l trucks temp gauge has an extra resistor inline with the sensor so it reads colder than normal. From what I read people speculate that with a big load it would push into the hot area and could spook some owners so they opted to lower the reading on the gauge. On mine, it runs about 1/4 the gauge lower than the middle "normal" spot and people say the gas trucks run dead center.

Of course there are a lot of factors we haven't settled on yet. How steep is the grade in question? (5%, 7%, 10%?). We've mentioned speeds from 35mph to 75mph, but what exact speed are we talking about? How much load exactly?

I've driven from 56hp to over 200hp vehicles that have enough load to need 100% throttle at high RPM's (lowest gear possible) and still can't keep up with the speed limit. Of course then you have to factor in that we have less cooling capacity up here because the air is thin and dry going over 11,000ft and higher mountain passes.

Lots of factors, lots of vehicles, lots of scenarios. Maybe for most people 30mph to 35mph the fan doesn't do a thing to help. But maybe for other vehicles and situations it's a bit higher speed than that. How much? The world may never know (now I want a Tootsie Pop.)

And in the end, as long as your truck doesn't overheat that's all that matters.

[Tahoe_Hybrid]

Originally Posted by ps2fixer

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 =).

7.3L is about 10-11MPG on average so 26.6 is incorrect... the best bet is to find a wreaked newer diesel that is a 4 banger.... most of those 4 banger are getting 30-35ish in pickups...


the top part of the gas tank is larger i burn 15 of 25.5 gallons before it hits the 1/2 mark on my tahoe

[Isaac Zachary]

Originally Posted by Tahoe_Hybrid

7.3L is about 10-11MPG on average so 26.6 is incorrect... the best bet is to find a wreaked newer diesel that is a 4 banger.... most of those 4 banger are getting 30-35ish in pickups...


the top part of the gas tank is larger i burn 15 of 25.5 gallons before it hits the 1/2 mark on my tahoe

10-11mg in a diesel sounds depressing seeing how there are a few getting up to 15mpg in V8 gasoline trucks of similar sizes. Not that there wouldn't be an advantage with the 4 banger.

I wonder if it would be advantageous to deactivate certain cylinders in a large diesel. The more the load the more effcient so maybe that would help. ?? I guess it depends on the type of injection system, whether it's a common rail or an injector pump, for an example.

With an injector pump, adding a few extremely high pressure 12V solenoid valves on certain injector lines and then routing that back into the fuel return would do the trick.

There may be problems with the turbo spooling correctly when running on just a few cylinders though. Maybe multiple staged turbos would do the trick. ??

[Tahoe_Hybrid]

Originally Posted by Isaac Zachary

10-11mg in a diesel sounds depressing seeing how there are a few getting up to 15mpg in V8 gasoline trucks of similar sizes. Not that there wouldn't be an advantage with the 4 banger.

I wonder if it would be advantageous to deactivate certain cylinders in a large diesel. The more the load the more effcient so maybe that would help. ?? I guess it depends on the type of injection system, whether it's a common rail or an injector pump, for an example.

With an injector pump, adding a few extremely high pressure 12V solenoid valves on certain injector lines and then routing that back into the fuel return would do the trick.

There may be problems with the turbo spooling correctly when running on just a few cylinders though. Maybe multiple staged turbos would do the trick. ??

1-4-6-7 (enabled) is what GM uses for AFM
2-3-5-8 are disabled...

[ps2fixer]

Originally Posted by Tahoe_Hybrid

7.3L is about 10-11MPG on average so 26.6 is incorrect... the best bet is to find a wreaked newer diesel that is a 4 banger.... most of those 4 banger are getting 30-35ish in pickups...


the top part of the gas tank is larger i burn 15 of 25.5 gallons before it hits the 1/2 mark on my tahoe

Tell that to my fuel usage vs distance traveled. I know the fuel tanks aren't great for being consistent so that tank might be abnormally high, but not quite that much. The next tank ended up being around 16mpg, averaged together it's still 20mpg, double of what you state.

I don't drive the truck like I stole it, it's a stick, and it's got the highest geared axle it could come with stock, 3.55. The topper on it helps slightly with areo. My dad's is the same thing but 4.10 gearing, no topper, and he was getting 15mpg with a tuner and beating the snot out of it. Both trucks have stock sized tires, not 40in like a lot of people like to do.

Generally speaking, the physical shape of a fuel/gas tank is tapered in at the top, so it should hold less fuel at the top vs the bottom. However if you're using the fuel gauge, then it depends how the OE company designed the float in the tank. I've had vehicles that were very linear like my corolla, while my dad's Camry goes 80+ miles before coming off full. Tank mounted angle and a ton of factors effect the reading including the wiring, connectors etc. It's a resistive based reading.

Anyway, as I drive the truck more, the mpg I'm getting should average out and become more and more accurate. Ball park 20mpg is right in the range I see a lot of people claiming with similar gearing and similar speeds.

Remember, this isn't the 7.3 IDI engine, it's the power stroke. It injects the fuel at much higher pressure which makes it burn better, plus the computer has more control over timing and such. I've seen some claims that the IDI's can do alright, but that's with modifying timing and injection amounts (like tuning a carb).

Empty a 4 cylinder would give better mpg I'm sure, but make the whole vehicle weight 19k lbs and that 4 banger will have a heck of a time with hills. 7.3L isn't my first pick for engine size, there's no real happy medium in the diesel world for Ford's. A cummins swap could give better mpg, but the cost of another truck, doing the swap etc will likely far outweigh any fuel savings I'd have. No point in spending a $1 to save $0.01.

Originally Posted by Isaac Zachary

10-11mg in a diesel sounds depressing seeing how there are a few getting up to 15mpg in V8 gasoline trucks of similar sizes. Not that there wouldn't be an advantage with the 4 banger.

I wonder if it would be advantageous to deactivate certain cylinders in a large diesel. The more the load the more effcient so maybe that would help. ?? I guess it depends on the type of injection system, whether it's a common rail or an injector pump, for an example.

With an injector pump, adding a few extremely high pressure 12V solenoid valves on certain injector lines and then routing that back into the fuel return would do the trick.

There may be problems with the turbo spooling correctly when running on just a few cylinders though. Maybe multiple staged turbos would do the trick. ??

Cylinder deactivation would be a neat concept on a diesel. I wouldn't trust Ford's electronics to do a good job though if it was designed that way from the factory (like their gas 8-6-4 setups, people always seem to have problems with it). I suspect an cylinder not getting fuel for extended times might have excess wear, but I don't know how the oil circuits are in the 7.3L. Moving the "dead" cylinders around would offset that issue, but then it takes a fast computer to process which cylinders to kill and such.

Ironically, I had a through of what the 7.3L would be like as a 4 cyl. It would turn into a 3.65L. I saw a video of someone reworking an engine and claiming to recover enough heat out of the engine to not need a radiator. If I remember right, one of the engines he did was the 4.3L v6, but turned it into a 3 cylinder. The head was removed and I suspect a block off plate was added, not sure how the actual cylinder deactivation was done, might have removed the pistons, or maybe they were left in to keep balance. I can't seem to find the video or any pages about it now. I do remember one of the things he did with the heat was pre-heat the gas coming into the engine. If I remember right, the target was just below the boiling point, or maybe it was over the boiling point but under pressure where it didn't boil till sprayed into the cylinder. I figured it was more on the lines of conspiracy theory, but I don't think the guy was claiming super crazy numbers and he converted several engines.

Anyway, a 3.65L that was tuned a bit hotter than factory with a turbo that works well with it and intercooler might meet my needs for hauling and give good mpg while empty. Most 4 cyl engines seem to be half that size so it would probably have a nice vibration running too lol.

[cRiPpLe_rOoStEr]

Originally Posted by ps2fixer

Anyway, a 3.65L that was tuned a bit hotter than factory with a turbo that works well with it and intercooler might meet my needs for hauling and give good mpg while empty.

Brazilian turbodiesel versions of the F-250 had either a 3.9L Cummins 4-cyl or a regionally-sourced MWM 4.2L straight-6. I have no experience with the straight-6, yet I drove smaller trucks (Nissan Frontier D22 and XTerra, and S10) fitted with a 4-cyl 2.8L based on the same design. My only experiences with the F-250 were with the Cummins, and it was quite good.

[ps2fixer]

I don't know Dodge too great, but looks like the US options was a 5.9L and later a 6.7L and I'd need a 2003+ truck, maybe even newer to get away from the "cumapart" era of the engine, unless that's the newer engines and the old ones were the reliable ones.

I wonder what other applications used the 3.9L Cummings. Kind of late now since I already own the 7.3L but would be interesting to read a bit more about it assuming it's used in the US in something. Never understood why the US has hardly any diesel options. I guess they require a little more attention (like starting temps, block heater etc) and people here on average are too lazy for that. Why else would automatics dominate the market here, while most other countries manuals are still very strong (from what I read atleast).

I'm not even sure if there's a small pickup here offered with a diesel engine. My neighbor mentioned a Chevy Luv with a diesel in it when he was a teen. I know Toyota had a diesel in their 80's era pickups but extremely uncommon here and a running truck is like $4k+ while a gas one is $1-1.5k in my area in similar shape.

I know the big Ford trucks had an option to come with a Cummins, know next to nothing about them though. The GVWR would be too high for me to use the truck directly, but an engine swap could be interesting thing to ponder. I'm sure those trucks have horrible MPG, but they also have very low geared axles for hauling massive loads.

Random/interesting idea, take a 5.9/6.7L cummings, disable 3 cylinders (and keep it balanced yet) and throw it in a small vehicle, small truck or rwd car. Could give impressive mpg while still being fairly powerful. Small diesel engines in vehicles seem to be so uncommon that, that route would almost make sense.