2007 Isuzu NPR gas 5-6mpg????

Discussion in 'Trucks and Trailers' started by replenish&subdue, Sep 29, 2008.

  1. replenish&subdue

    replenish&subdue LawnSite Senior Member
    Messages: 272

    I am really bummed out. Bought a 07 gas NPR and get 5-6 mpg. The dealer thought I should get 10-11 at least even with all the weight I took I carried. My employee drives like a granma.
    What should I be getting anyhow and any clues how to get better mileage.
    Thanks beforehand,
  2. TXNSLighting

    TXNSLighting LawnSite Fanatic
    from DFW, TX
    Messages: 6,463

    Thats what ya get for buying a gas engine!
  3. nosparkplugs

    nosparkplugs LawnSite Gold Member
    Messages: 3,444

    The 6.7L gasburner is a gas guzzler:laugh:, the diesel costs more; however you would be getting the 10-11 mpg` maybe more with the diesel. Your stuck with 5-6mpg, Beauty Lawn Service is not happy with their gasburner 6.7 NPR's either.

    You could switch to synthetic lubricant; engine,transmission,rear diff; which will increase mpg anywhere from 1 to 5mpg.

    If all possible trade it for the diesel NPR, thats going to be the best investment in the long haul, and get you the mpg you want.

    Good Luck
  4. replenish&subdue

    replenish&subdue LawnSite Senior Member
    Messages: 272

    Yeah,but from the threads I read most have said deisal will cost more in maintenance,fuel and the gas has more ump.Sure better resale value but I expect to keep this truck till the world ends.I have a Ford 250 deisal which is great on fuel.I wanted a Isuzu to put a 500 gal. tank with all the extra.
    Thanks for the good reply and helpful advice to increase mileage.
  5. 1cooltreeguy

    1cooltreeguy LawnSite Senior Member
    Messages: 630

    I have a great diesel NPR - 12-15 mpg hauling mowers and loaded. Sorrry bout your luck....
  6. TXNSLighting

    TXNSLighting LawnSite Fanatic
    from DFW, TX
    Messages: 6,463

    Its DIESEL. They dont cost that much more to maintain either...And they have plenty get up and go. Well i dont know about they isuzus, but my diesel has alot more get up and go than a gas engine.
  7. HenryB

    HenryB LawnSite Bronze Member
    Messages: 1,853

    I've got two of the same trucks NPR Deisels I get 8-10 mpg empty. My gas NPR gets 5-6. My Ford F150 gets 9-11 local. I don't think most guys are honest with themselves about their MPG. Sadly I am and my numbers show it:cry:
  8. nosparkplugs

    nosparkplugs LawnSite Gold Member
    Messages: 3,444

    thats a total myth, that diesels cost more in maintenance, modern diesels out performs the gasoline engine in any class of truck. Diesels hold their resale value more than a comparable gasoline model. Diesels will virtuly suck the paint off a comparable gasoline model going up a hill. Diesels have the real power to tow or haul weight.

    Took this off Wikipedia, saved me some typing.

    Diesel engines are more efficient than gasoline engines of the same power, resulting in lower fuel consumption. A common margin is 40% more miles per gallon for an efficient turbodiesel. For example, Volkswagen Group engines, has a combined Euro rating of 38 miles per US gallon (6.2 L/100 km) for the 102 bhp (76 kW) gas engine and 54 mpg (4.4 L/100 km) for the 105 bhp (78 kW) diesel engine. However, such a comparison doesn't take into account that diesel fuel is denser and contains about 15% more energy by volume. Although the calorific value of the fuel is slightly lower at 45.3 MJ/kg (megajoules per kilogram) than gasoline at 45.8 MJ/kg, liquid diesel fuel is significantly denser than liquid gasoline. This is important because volume of fuel, in addition to mass, is an important consideration in mobile applications. No vehicle has an unlimited volume available for fuel storage.

    Adjusting the numbers to account for the energy density of diesel fuel, one finds the overall energy efficiency of the aforementioned paragraph is still about 20% greater for the diesel version, despite the weight penalty of the diesel engine.

    While higher compression ratio is helpful in raising efficiency, diesel engines are much more efficient than gasoline engines when at low power and at engine idle. Unlike the gasoline engine, diesels lack a butterfly valve (throttle) in the inlet system, which closes at idle. This creates parasitic loss and destruction of availability on the incoming air, reducing the efficiency of gasoline engines at idle. In many applications, such as marine, agriculture, and railways, diesels are left idling unattended for many hours or sometimes days.

    Diesel engines usually have longer stroke lengths to achieve the necessary compression ratios. As a result piston speeds are higher and more force must be transmitted through the connecting rods and crankshaft to change the momentum of the piston. This is another reason that a diesel engine must be stronger for the same power output.

    Yet it is this same build quality that has allowed some enthusiasts to acquire significant power increases with turbocharged engines through fairly simple and inexpensive modifications. A gasoline engine of similar size cannot put out a comparable power increase without extensive alterations because the stock components would not be able to withstand the higher stresses placed upon them. Since a diesel engine is already built to withstand higher levels of stress, it makes an ideal candidate for performance tuning with little expense. However, it should be said that any modification that raises the amount of fuel and air put through a diesel engine will increase its operating temperature which will reduce its life and increase service requirements. These are issues with newer, lighter, high performance diesel engines which are not "overbuilt" to the degree of older engines and are being pushed to provide greater power in smaller engines.

    The addition of a turbocharger or supercharger to the engine greatly assists in increasing fuel economy and power output, mitigating the fuel-air intake speed limit mentioned above for a given engine displacement. Boost pressures can be higher on diesels than gasoline engines, due to the latter's susceptibility to knock, and the higher compression ratio allows a diesel engine to be more efficient than a comparable spark ignition engine. Because the burned gases are expanded further in a diesel engine cylinder, the exhaust gas is cooler, meaning turbochargers require less cooling, and can be more reliable, than on spark-ignition engines.

    The increased fuel economy of the diesel engine over the gasoline engine means that the diesel produces less carbon dioxide (CO2) per unit distance. Recently, advances in production and changes in the political climate have increased the availability and awareness of biodiesel, an alternative to petroleum-derived diesel fuel with a much lower net-sum emission of CO2, due to the absorption of CO2 by plants used to produce the fuel. Although concerns are now being raised as to the negative effect this is having on the world food supply, as the growing of crops specifically for biofuels takes up land that could be used for food crops and uses water that could be used by both humans and animals. The use of waste vegetable oil, sawmill waste from managed forests in Finland funded by Nokia venture capital, and the development of the production of vegetable oil from algae, demonstrate great promise in providing feed stocks for sustainable biodiesel, that are not in competition with food production.

    The two main factors that held diesel engine back in private vehicles until quite recently were their low power outputs and high noise levels, characterised by knock or clatter, especially at low speeds and when cold. This noise is caused by "piston slap", the sudden ignition of the diesel fuel when injected into the combustion chamber slamming the cold-contracted piston into the cylinder wall. The tolerances between the piston and cylinder wall are greater at cold temperatures to allow expansion at higher temperatures. A combination of improved mechanical technology (such as multi-stage injectors which fire a short "pilot charges" of fuel into the cylinder to warm the combustion chamber before delivering the main fuel charge), higher injection pressures that have improved the atomisation of fuel into smaller droplets, and electronic control (which can adjust the timing and length of the injection process to optimise it for all speeds and temperatures), have mostly mitigated these problems in the latest generation of common-rail designs, while greatly improving engine efficiency. Poor power and narrow torque bands have been addressed by the use of superchargers, turbochargers, (especially variable geometry turbochargers), intercoolers, and a large efficiency increase from about 35% for IDI to 45% for the latest engines in the last 15 years.

    Even though diesel engines have a theoretical fuel efficiency of 75%, in practice it is less. Large diesel trucks, buses, and newer diesel cars can achieve efficiencies around 45%,[4] however they could reach 55% efficiency in the near future.[5]

    Diesel engines produce very little carbon monoxide as they burn the fuel in excess air even at full load, at which point the quantity of fuel injected per cycle is still about 50% lean of stoichiometric. However, they can produce black soot (or more specifically diesel particulate matter) from their exhaust, which consists of unburned carbon compounds. This is caused by local low temperatures where the fuel is not fully atomized. These local low temperatures occur at the cylinder walls and at the outside of large droplets of fuel. At these areas where it is relatively cold, the mixture is rich (contrary to the overall mixture which is lean). The rich mixture has less air to burn and some of the fuel turns into a carbon deposit.

    The full load limit of a diesel engine in normal service is defined by the "black smoke limit." Beyond which point the fuel cannot be completely combusted, as the "black smoke limit" is still considerably lean of stoichiometric. It is possible to obtain more power by exceeding it, but the resultant inefficient combustion means that the extra power comes at the price of reduced combustion efficiency, high fuel consumption and dense clouds of smoke. This is only done in specialized applications (such as tractor pulling competitions) where these disadvantages are of little concern.

    Likewise, when starting from cold, the engine's combustion efficiency is reduced because the cold engine block draws heat out of the cylinder in the compression stroke. The result is that fuel is not combusted fully, resulting in blue/white smoke and lower power outputs until the engine has warmed through. This is especially the case with indirect injection engines, which are less thermally efficient. With electronic injection, the timing and length of the injection sequence can be altered to compensate for this. Older engines with mechanical injection can have manual control to alter the timing, or multi-phase electronically-controlled glow plugs, that stay on for a period after start-up to ensure clean combustion—the plugs are automatically switched to a lower power to prevent them burning out.

    Particles of the size normally called PM10 (particles of 10 micrometres or smaller) have been implicated in health problems, especially in cities. Some modern diesel engines feature diesel particulate filters, which catch the black soot and when saturated are automatically regenerated by burning the particles. Other problems associated with the exhaust gases (nitrogen oxides, sulfur oxides) can be mitigated with further investment and equipment; some diesel cars now have catalytic converters in the exhaust.

    All diesel engine exhaust emissions can be significantly reduced by the use of biodiesel fuel. Oxides of nitrogen do increase from a vehicle using biodiesel, but they too can be reduced to levels below that of fossil fuel diesel, by changing fuel injection timing.

    Power and torque
    For commercial uses requiring towing, load carrying and other tractive tasks, diesel engines tend to have better torque characteristics. Diesel engines tend to have their torque peak quite low in their speed range (usually between 1600–2000 rpm for a small-capacity unit, lower for a larger engine used in a truck). This provides smoother control over heavy loads when starting from rest, and, crucially, allows the diesel engine to be given higher loads at low speeds than a gasoline engine, making them much more economical.

    The lack of an electrical ignition system greatly improves the reliability. The high durability of a diesel engine is also due to its overbuilt nature as well as the diesel's combustion cycle, which creates less-violent changes in pressure when compared to a spark-ignition engine, a benefit that is magnified by the lower rotating speeds in diesels. Diesel fuel is a better lubricant than gasoline so is less harmful to the oil film on piston rings and cylinder bores; it is routine for diesel engines to cover 250,000 miles or more without a rebuild.

    Due to the greater compression force required and the increased weight of the stronger components, starting a diesel engine is harder. More torque is required to push the engine through compression.

    As mentioned above, diesel engines tend to have more torque at lower engine speeds than gasoline engines. However, diesel engines tend to have a narrower power band than gasoline engines. Naturally-aspirated diesels tend to lack power and torque at the top of their speed range. This narrow band is a reason why a vehicle such as a truck may have a gearbox with as many as 18 or more gears, to allow the engine's power to be used effectively at all speeds. Turbochargers tend to improve power at high engine speeds; superchargers improve power at lower speeds; and variable geometry turbochargers improve the engine's performance equally by flattening the torque curve.
  9. ericmcj31

    ericmcj31 LawnSite Senior Member
    Messages: 404

    That SUCKS!! I bought a '99 (Diesel) in 2000 new, and I was REALLY disappointed to see that I only got about 11 MPG. I hear the manual shifters get better mileage. I have since bought an '01 and it is the same engine and all, but gets about 13-14 MPG's (loaded down). I also have an '06 and it gets along the lines of the '01 's MPG-about 14 or so. One thing I have noticed on all NPR's I have owned, and it is really weird and makes no sense, but I actully get better MPG around town with moderate stop and go-than on the highway. May be b/c I have it hammered down on the highway and I go pretty slow through town, but not like a g'ma. Good luck and 5-6MPG's SUCK!!! I can't believe that 's all it gets. I've got a buddy looking for a gas-burner and I'll pass the word. I'd trade it for a diesel, myself! Yeah it is higher to change oil, filters, etc.--, but is worth it in (obviously) fuel consumption, power, and life-(you were talking about keeping it until the world ends, then by far diesel is the way to go)!
  10. lawn king

    lawn king LawnSite Silver Member
    Messages: 2,413

    My npr turbo diesel only has 175 hp, but its the best work truck i ever owned. 13 mpg, xm,ac,auto, it turns on a dime, dumps, plows snow, hauls my 5000 lb kubota, its very reliable, whats not to like.

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