Gas versus Diesel by Mark Polk..
Hi my name is Mark Polk. I am the owner of a company called RV Education
101. We produce videos on how to use and maintain Recreation Vehicles,
and I am the author of a book titled “The RV Bookâ€. I started the
company because I was concerned about the lack of education and safety
awareness for the RV consumer. To view our complete line of products
please visit our website at http://www.rveducation101.com/
This article discusses an age old question and one I get asked a lot, should I buy gas or diesel?
This question has fueled many a heated debates too. Sometimes this
question involves a truck that will be used to tow a trailer, and other
times it involves what type of motorhome to purchase. A universal
response you could expect to hear to this question goes something like
this: Diesels cost more. 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’re 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 mainly due to
advancements in gasoline RV chassis’ design; with greater Gross
Vehicle Weight Ratings (GVWR) to accommodate coach designs with 3 and 4
slideouts. And don’t forget to factor in the new technology in
gasoline engine and transmission design over the past several years.
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 these higher prices. You are moving to a much
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 between gas and diesel motorhomes, what
are we really talking about when it comes down to gas versus diesel? Say
for example in a truck you want to use to pull 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.
Torque can be multiplied through gear ratios. You have probably heard
that the higher the real axle gear ratio is the better the truck will
tow. The axle ratio is the number of times the driveshaft must rotate to
turn the rear wheels one time. If you have a 3.73:1 axle ratio the
drive shaft turns 3.73 times for each full turn of the axle. So in a
sense torque really equals towing capacity.
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 raise so does the horsepower. When you are towing a trailer the
engine speed is more likely to be in the low to mid 2,000 RPM range,
which means you probably have slightly more than half of the 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. In reality it is measuring torque
in pound-feet and converting it to horsepower. Even at the rated peak
power RPM you won’t really 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.
Q&A
Question: Why does a diesel engine have more torque?
Mark Says: Much of the reason is in the way the engine is
designed. Internal combustion engines use spark from a spark plug to
ignite fuel in the combustion chamber of a gasoline engine and the high
heat from compression to ignite the fuel in a diesel engine. It’s more
difficult to burn diesel fuel so diesel engines have higher compression
ratios resulting in more heat to ignite the fuel and more power.
Question: I have always heard that a diesel engine is much louder than a gas engine, is this true?
Mark Says: If you asked me that several years ago the answer would have been yes, but newer diesel engines are actually very quiet.
Question: You said in the article a diesel motorhome rides better, why is that?
Mark Says: Most gas motorhome chassis’ use leaf spring
suspension systems. With this suspension system you will experience
things like “body roll†and “pitch.†whenever pressure is
exerted against one side of the motorhome. It can be caused by a gust of
wind, a shift in weight while cornering, or a passing truck. The
effects of sway on a motorhome are increased because of the height and
mass of the motorhome. A diesel chassis uses an air ride suspension
system. These systems keep the chassis adjusted to the proper ride
height at all times by adding and releasing air as required. And the way
the system is designed eliminates the pitch and roll affect you get
from leaf spring suspensions, resulting in a smoother riding motorhome.
Happy Camping,
Mark J. Polk
Copyright by Mark J. Polk owner rveducation101.com
RV Expert Mark Polk, seen on TV, is the producer & host of
America’s most highly regarded series of DVD’s, videos, books, and
e-books. http://www.rveducation101.com/
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