Gas Vs Diesel

July 16, 2008

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July 16, 2008

Should I buy gas or diesel? This question has fueled many a heated debate over the years. A universal response you could expect to hear to this question goes something like this; diesels cost more than gas, don’t buy a diesel unless you plan to put a bunch of miles on it and keep it for a long time. That’s the only way you can justify the extra cost of a diesel.

Several years ago there was some truth to this somewhat typical response. But things are changing, especially when you are talking about motorhomes. Today, the cost of some gasoline powered motorhomes is about the same as many of the entry level diesel motorhomes available on the market. This higher cost is associated with advancements in gasoline RV chassis’ design; with greater Gross Vehicle Weight Ratings (GVWR) to accommodate coach designs offering 3 and 4 slideouts on the RV. And don’t forget to factor in new technology in gasoline engine and transmission design over the past several years too.

The old response, of diesels costing more, does hold true with some of the specialized diesel chassis manufacturers, but it’s not just the engine that accounts for the higher price tag. You are moving to a higher plateau across the board. For the most part gasoline RV chassis’ are heavy duty truck chassis’ modified for Recreation Vehicle use, whereas many diesel chassis’ are a bus chassis. These bus chassis’ have even greater GVWR’s, air brakes, air ride suspension systems, larger transmissions, rear mounted diesel engines and more. They handle better, ride better and cost more. I always say you get what you pay for.

Other than the cost factor, what are we really talking about when it comes down to gas versus diesel? Say for example, in a truck you plan to use for towing a trailer. This is where we need to factor in the engine itself. This is also where torque and horsepower come into the equation.

Explaining torque and horsepower can get extremely technical, and we want to keep this simple and easy to understand. With that said, torque is basically the force or energy required to move something. Torque is the measurement of force, and force is measured in reference to a twisting or rotating shaft. In English terms torque is measured in pounds-feet, but is more commonly referred to as foot-pounds. So in keeping it simple let’s just say that torque can be thought of as the amount of turning force it takes to move one pound of weight the distance of one foot.

Horsepower on the other hand is torque X RPM’s. Torque is how much work is being done, and horsepower is how fast you get the actual work done. What’s interesting is, an engine rated at 350 horsepower only produces that horsepower at a rated peak power RPM. This RPM range, for a gasoline engine, is often between 5,000 and 6,000 RPM’s. When an engine is idling the horsepower is significantly lower, and as the RPM’s increase so does the horsepower. When you are towing a trailer the engine speed is more likely to be in a lower RPM range, which means you have much less available horsepower than the engines rated horsepower. Horsepower is measured by a dynamometer. A dynamometer puts a load on the engine and measures the amount of power the engine produces against the load at various speeds. Even at the rated peak power RPM you really won’t get the rated horsepower, because a percentage is lost through auxiliary equipment on the engine and the process of getting it back to the wheels.

In a diesel engine the horsepower peaks at a lower RPM, and there is more torque at a lower RPM compared to a gasoline engine. This results in a diesel engine having much more power at a lower RPM, around the RPM range you will be towing at. This higher torque and higher horsepower at a lower RPM equates to better towing.

There are many other factors involved in the question of gas versus diesel that you will need to consider. What are the maintenance costs involved, cost difference between fuel types, fuel economy, your budget, and the resale value? Whether it’s for a tow vehicle or a motorhome, take your time and make a well informed decision when comparing gas to diesel.

If the question is which truck will tow more or which motorhome has more torque the diesel will win hands down, but I honestly have no complaints with our gas powered motorhome either. Especially when considering the price!

Happy Camping

Mark Polk

RV Education 101