Diesel mileage

[Sludgy]

During a longish trip to New Hampshire to climb Mount Monadnock, my wife and I took the F350 diesel/automatic. For shorter trips we always take her Corolla, but I get leg cramps in it on long drives. I'm already on Coumadin for a blood disorder, so leg cramps are not simply uncomfortable for me. They're dangerous.

Anyway, with the Scangage and careful driving, the beast only got 17 mpg. To say the least, I've been very unhappy with this truck, as my Chevy 5.0 and GMC 4.3 liter trucks got better mileage, without the $5000 diesel option. And I still have 2 years of payments left on this P.O.S. grrrrrrrr

A question: Several companies make diesel ECU programmers that claim more HP and better mileage. Has anybody here used them? Did they help improve mileage?

[Joe Gardner]

My brother had a Dodge Cummins 2500, he consistantly was getting 21 - 22mpg freeway. He had his ECU programmed for better millage when his job location was re-located another 40 miles out of town. From that point out he was getting 24 - 25mpg consistantly. And would only get sub-20 when towing his jeep to Moab.

I think the cost was just north of $100, but for a 3 - 4 mpg increase, it was worth it.

[Joe Gardner]

BTW, that 2500 had 300K miles when he bought it, and 460K when he sold it. He sold it for $1K less then purchase price. IMHO the big reason to keep the diesel around is for the long life of the engine / truck. Resale is going to be worth a bit more as well. Something else to think about. :)

[Bunger]

A question: Several companies make diesel ECU programmers that claim more HP and better mileage. Has anybody here used them? Did they help improve mileage?

Yup! Those programmers are awesome!!! I've seen 4-5 people increase mileage a decent amount and also see HUGE increases in power. My buddies dad installed one on his Dodge and said that it paid for itself in the first 3 months, just from the mileage increase! I'd say do a little research and pick yourself up one.

[rh77]

I used to drive an E-350 non-turbo (1996?) which got in the low 20's if I remember right. When the fleet was upgraded to E-350's with the PowerStroke Diesel, the turbo alone sucked the fuel down and generated SO much more power than the standard V-8 diesel -- but more power = more fuel.

I think the secret might be to get a programmable chip or Engine Management System that regulates the turbo pressure, among other factors. You're at an advantage because of the wide range of chips/controllers available. A programmable one could reduce power and increase economy for commutes and long trips, but also be able to switch to a higher turbo psi and fuel pressure for towing, etc.

Also, reduced cruise speed will help with the high drag on pickups.

RH77

[molecule]

mt. monadnock is a nice hike
you can see mt. washington snow peak on any decent day
i've heard with a set of binocs and an illegal night of camping you can see the tip of the prudential building in boston
lol

[Sludgy]

WAI helps mileage, but my turbodiesel has an intercooler that cools the intake! Can I get better mileage by bypassing the intercooler?

[rh77]

WAI helps mileage, but my turbodiesel has an intercooler that cools the intake! Can I get better mileage by bypassing the intercooler?

The intercooler is there to cool the incoming air so the ECU can use added turbo boost (cool air allows more pressure without the risk of detonation) and more power is available. Warm air would cause the ECU to reduce the boost because of the risk of pinging and detonation, and reduce power. I'm not sure what the limits would be on how hot it would have to get, and if it would dump more fuel in the charge to make it run more rich and prevent catastrophe. I'm thinking that Diesels are susceptible to detonation like gassers. Maybe I'm off. Do you ever get black smoke from the exhaust? If you disconnect the IC as a test and draw in hot engine air, then a trail of black exhaust (as seen in the side mirror) shows that you're pumping more fuel in there. Do you have a ScanGuage or something to monitor engine variables?

RH77

[DaX]

The intercooler is there to cool the incoming air so the ECU can use added turbo boost (cool air allows more pressure without the risk of detonation) and more power is available. Warm air would cause the ECU to reduce the boost because of the risk of pinging and detonation, and reduce power. I'm not sure what the limits would be on how hot it would have to get, and if it would dump more fuel in the charge to make it run more rich and prevent catastrophe. I'm thinking that Diesels are susceptible to detonation like gassers. Maybe I'm off. Do you ever get black smoke from the exhaust? If you disconnect the IC as a test and draw in hot engine air, then a trail of black exhaust (as seen in the side mirror) shows that you're pumping more fuel in there. Do you have a ScanGuage or something to monitor engine variables?

RH77

By no means am I a diesel mechanic, but don't diesels run off the concept of detonation? My (limited) understanding is that a diesel is a "pre-ignition" engine, as it does not have spark plugs and ignites the fuel simply on combustion chamber temperatures and compression of the fuel. I have seen turbo diesel trucks run 120+ psi of boost.

[rh77]

By no means am I a diesel mechanic, but don't diesels run off the concept of detonation? My (limited) understanding is that a diesel is a "pre-ignition" engine, as it does not have spark plugs and ignites the fuel simply on combustion chamber temperatures and compression of the fuel. I have seen turbo diesel trucks run 120+ psi of boost.

Yeah, I was thinking of that. I guess the turbo pressure and fuel pressure may be the variables of interest. At tractor-pulls or similar events, huge turbos and massive amounts of fuel are pumped: result = LOTS of black smoke. Same with guys who add more powerful fuel pumps to their Dodge/Cummins trucks -- more power and more black smoke. So then it would be reasonable to assume that hotter air does what? I'll have to look this one up...

RH77

[rh77]

Alright, I took this from the Volkswagen TDI club (http://tdiclub.com)website -- I was an active member there when I was close to buying a Golf Diesel.

(I stand corrected about the detonation stuff)

"Air is drawn through a conventional air filter and into the so-called MAF, or mass-air-flow meter. A hot wire (older models) or hot film (later models) is contained inside this sensor and is maintained at a constant temperature. The electrical current which is required to maintain this temperature is an indication of how much airflow is passing over the sensing element. After the MAF, a hose connection comes from the valve cover where crankcase fumes are drawn into the intake air. From there, the intake air is drawn into the compressor of the turbocharger...where it is compressed, but the compression process also increases the temperature of the air. The hot compressed air passes through a small heat exchanger known as the intercooler. When heat is removed, the density of the air increases, thus increasing the amount (by mass) of air which is drawn into the engine. The objective is to make the air going into the engine cylinders as dense as possible (pressurized and cooled) to allow maximum power output. From the intercooler, the pressurized and cooled air goes to the intake manifold where it is mixed with a proportion of exhaust from the EGR (exhaust gas recirculation) system for emission control purposes. (The EGR system is connected on the high-pressure side of both the exhaust and intake systems.) This mixture then goes into the engine cylinders. Unlike with a gasoline engine, there is no throttle in a diesel engine. Power output is governed using the fuel supply only. The lean air/fuel mixture is one of the reasons that the diesel engine is so efficient, and the lack of intake restriction due to absence of a throttle reduces pumping losses, and that is another reason that a diesel engine is more efficient when running under part load."

OK, so hotter air would probably reduce power by reducing fuel pumpage -- that's my guess, and FE would increase. It's worth a try to bypass the intercooler and do an experiment (depending on how hard it is, and if you can keep the air clean -- post-filter mods need to be clean and well-made, especially with the high temperature and pressure of post-turbo operations).

I recommend the FAQ page (http://tdiclub.com/TDIFAQ/TDiFAQ-1.html) from where I got this info -- very informative. Bear in mind that you have a "Common Rail" instead of "Direct-Injection" Diesel.

RH77

[DaX]

Unlike with a gasoline engine, there is no throttle in a diesel engine. Power output is governed using the fuel supply only.

Holy cow...I never knew that!

[Sludgy]

Just got back from a trip to turkey hunting trip to Potter Mountain north of Pittsfield MA. I got 18.5 mpg in the F350, doing nothing differently than the trip to Monadnock....... 18.5 sucks, I suppose it's better than the 17 to NH.

[philmcneal]

can you bump start on a diesel? can it be abused even if the diesel has turbo?

[rh77]

There's a lot more torque and compression to bump and the turbo doesn't like to be immediately shut-down -- oil tends to sizzle on the hot bearings when they stop immediately and will kill the turbine over time. To get more than 100K miles out of a turbo, you need to idle it for at least 30-seconds if not a minute, based on oil temp. I had a timer on the EVO that would calculate the time based on oil temp and RPM -- you just turned off the car, locked it and walk away -- it would shut down automatically after the preset time. A waste of gas, but definitely a turbo saver.

My guess is, most late-model F-350 Diesels are automatics -- I assume yours is Sludgy? That would render bump start useless, but with the compression, Neutral coasting might help.

RH77

[Sludgy]

My diesel is an automatic. Push starting is impossible.

Cooking the turbo bearings doesn't usually happen unless you run the truck realy hard (like pulling a large trailer) and then shut down immediately. I'm pretty light on the pedal and run empty most of the time, so I don't worry about it much.

It was next to impossible to find a diesel with a manual transmission "on the lot". I did find one at a dealer, but it didn't have A/C or a locking diferential, both of which I want. I suppose I could have ordered one from the factory, but I needed the truck right away for an off road vacation in northern Maine.

[philmcneal]

i heard diesels are much more efficent in idling in N as opposed to a petro. So maybe abusing N alone could be worth it to getting good mileage?

[rh77]

i heard diesels are much more efficent in idling in N as opposed to a petro. So maybe abusing N alone could be worth it to getting good mileage?

That makes sense -- the torque converter has to be huge to handle, well, all the extra torque. N would relieve the engine to have to spin that heavy connection.

[Sludgy]

According to the Scangage, my diesel uses 0.4 gph in N, when warm. In gear it's 0.6. It's much worse in cold weather, idling in gear at 1.2 or more.

I thought this was just due to high oil viscosity at low temps, but I just learned that Ford installed a valve in the exhaust pipe to choke the engine and make it work harder! This makes the engine warm up quicker.

My mileage drops off about 2 mpg in winter. Another reason for me to detest this Ford P.O.S.

[rh77]

According to the Scangage, my diesel uses 0.4 gph in N, when warm. In gear it's 0.6. It's much worse in cold weather, idling in gear at 1.2 or more.

I thought this was just due to high oil viscosity at low temps, but I just learned that Ford installed a valve in the exhaust pipe to choke the engine and make it work harder! This makes the engine warm up quicker.

My mileage drops off about 2 mpg in winter. Another reason for me to detest this Ford P.O.S.

Yeah, the old non-turbo Diesels I experienced took forever to warm-up -- the valve was probably an EPA mandated change to get things to less-polluting mode. As for the Winter mileage do you have a special blend of fuel to reduce emissions like the gasoline? Otherwise, you may need to warm the incoming air (in any season -- too high though, and you could get some pre-ignitions problems, I've read - depending on the flash point of Diesel fuel. I'd seriously look into bypassing the intercooler.

[Sludgy]

My truck threw a code and my "check engine" light came on yesterday. Took it to the dealer this morning, and they replaced the EGR valve under warranty.

I've driven it twice since then, and the tranny upshifts sooner than before. I can actually get into top geat at ~40 mph, where 45-50 was needed before. This should improve my mileage. I'll keep you posted.

[rh77]

My truck threw a code and my "check engine" light came on yesterday. Took it to the dealer this morning, and they replaced the EGR valve under warranty.

I've driven it twice since then, and the tranny upshifts sooner than before. I can actually get into top geat at ~40 mph, where 45-50 was needed before. This should improve my mileage. I'll keep you posted.

I'm guessing that the ECU was probably reset in the process and effects the shift pattern. At any rate, a new EGR could be the ticket to better mileage as well.

[Lug_Nut]

Bypassing the turbo diesel's intercooler is counter productive to fuel efficiency increases. Hot air can expand only so much, cold air can expand more.
Unlike most gasoline powered engines where hotter air will keep the air/fuel mix from coalescing prior to ignition, thus increasing burn efficiency enough to offset the loss of thermal expansion in a hotter air charge, a diesel has no fuel in the air until injection-ignition. A colder air charge is therefore preferable in a diesel due to the greater percent of expansion possible. Greater expansion pressure from the same fuel. Same pressure from less fuel.