It’s late Friday night and gently almost imperceptible a purring rumble pierces the evening air.
Softly breathing a deep seductive rumble.
Enthralling, distinctive and mesmerizing.
And yet … unmistakable.
The sound of another diesel pusher motorhome gliding thru the resort.
Majestic like a Bengal tiger head held high as it saunters confidently among the herd.
What is it that makes those diesels so damn desirable?
And, are they worth the extra cost?
What’s the difference between a gas and diesel powered motorhome?
Let’s begin with some basics and focus on engines commonly found in Vintage RVs.
The big bowtie is a common power plant used in GMs P30 chassis.
Specifically Chevrolets 454 big block V8.
The P30 chassis is found under many Vintage Class A motorhomes including the iconic silver bullet Airstream.
At 454 cubic inches (7.4 L) this engine was offered in several variations which are detailed on WIKI.
Beginning with its release in 1970 the base model 454 produced 390bhp and 500 ft lbs of torque.
Comparatively the Detroit 8V92 Diesel engine produced 435bhp and 1250 ft lbs of torque.
The numbers are slightly deceiving.
With just 45 ponies difference the horsepower is similar.
But, the increased torque of the diesel at more than double the gas engine is important.
That’s because torque does the work.
Lets examine why torque is critical.
The Caterpillar website provides an excellent explanation for horsepower, torque and the differences:
TORQUE IS FORCE CAUSING ROTATION, POWER IS HOW QUICKLY ROTATION OCCURS
That’s the simplest way of putting it, and even with that simple phrase, it’s clear that there is some overlap between torque and power, which is typically expressed as horsepower. A little more detail on the terms:
Torque – Torque is force, but not just any force. Specifically, it’s twisting force, which is measured in foot-pounds. In other words, torque is the measure of how many pounds of force are applied over a lever (like a crankshaft lever) of a certain length. A quick example: if an engine applies 200 pounds of force to a crankshaft level that is 2 feet long, it is producing 400 foot-pounds of torque.
In short, torque refers to an engine’s ability to perform work. The more torque it offers, the greater a load it can manage. So, for example, a torquey engine is one that usually provides a lot of work potential at low engine speeds. This characteristic allows operators to get a lot of acceleration.
Power – Power, which is represented as horsepower, is a measure of how fast an engine can deliver torque. Put another way, it’s the rate at which an engine can get work done. Torque is a factor in determining horsepower, so as the engine’s torque increases, so will its power. However, horsepower is also determined by the speed at which the engine is spinning, which is listed as rpm.
Horsepower best describes how fast an engine can apply force to a load. It increases as the engine’s torque increases, or as the speed of the engine in rpms increases. While torque is about acceleration, horsepower is about top speed.
With increased weight the gas engine struggles to maintain posted speeds.
When is Gas Power enough in a Motorhome?
The gas engines are very capable and have served reliably for many years.
Gas engines weigh substantially less than their diesel counterparts.
Often times 3-4 times less.
Gas engines are used in most cars, pickups and light duty trucks.
The sheer number of gas engines in service bods well for finding parts and service technicians.
Technicians with the training and skill to perform repairs and maintenance.
As a favorite power plant of hot rodders, there is a thriving market of performance parts and accessories for the gas engine.
With so many gas engines produced the chances are high that repair shops and salvage yards around the world have parts and replacements available.
So when is gas power enough?
When the engine is capable of maintaining safe speeds under average conditions.
What are average conditions?
When climbing mountains there are often lanes specifically for slow moving vehicles.
While climbing the mountains below the posted speed may be stressful it is common for large vehicles.
Just be aware that should your speed drop below 45mph flashers are courteous and sometimes required.
Flatlanders biggest concern is wind.
When crossing South Dakota it is common to experience high winds.
The type of winds the push semi tractor trailers onto their side.
If the motorhome is unable to maintain the posted speeds when pushing into a 20-30 headwind the travel will be slow, stressful and potentially dangerous to inattentive drivers.
Gas engines are enough when it can maintain safe speeds in average conditions.
When is Diesel Power Necessary for a Motorhome?
The move to diesel powered motorhomes becomes feasible and necessary as the size and weight of motorhomes increase.
There is no definitive threshold or requirement to switch to diesel power.
But when motorhomes exceed 30 feet long and 15,000 thousand pounds the benefits of torque really become obvious.
Diesel power becomes important when the weight of the motorhome exceeds the engines ability to maintain safe speeds.
This includes maintaining speed on level ground as well as when climbing hills in common conditions.
The design of many motorhomes are poor for cutting thru the wind.
Pushing a 40,000 pound brick on flat ground requires enough power to conquer the rolling resistance of the tires and air.
The Wanderlodge PT Definitive Guide
When climbing uphill the torque needed to move the motorhome increases.
And, the higher above sea level you go the thinner the air becomes.
These engines require massive amounts of air to burn fuel completely and produce the power needed.
So, as you climb the motor needs to work harder to maintain the same speed.
Don’t forget anything towed behind the motorhome adds weight.
Depending on your intended use the value of diesel power could begin at any size or length.
When in doubt choose more over less.
No one has complained about having more power.
Why Do Diesel Powered Motorhomes cost more?
The go-go process of a gas engine uses fuel, compression and spark to ignite the mixture.
The go-go process of a diesel engine uses fuel and extreme compression to ignite the mixture.
The combination of high compression ignition and the resulting torque force requires stronger guts.
The internal components are bigger, stronger and heavier.
This includes the engine block, heads and externals components.
More metal to withstand the stress which adds weight.
These requirements push the costs higher.
Its simple economics.
Are Diesel Powered Motorhomes Worth the Extra Money?
Diesel powered motorhomes are often loaded with luxury amenities.
High quality amenities seldom found in gas powered motorhomes.
Amenities like granite, marble or Corian countertops.
Solid wood cabinetry and tile covered floors.
And 4 cylinder diesel generators cable of powering a home with 12 to 20 kilowatts of electricity.
The typical owner of a diesel motorhome has previously owned at least 1 motorhome.
These owners want the best quality available which drives up cost and weight.
Lastly most diesel powered motorhomes retain a higher resale value.
Ultimately the choice and decision depends on the buyers desires.
If you want to travel the most comfortable way possible with all the comforts of home. Then the higher cost of diesel power is a small increase in the overall cost.
There is a point where diesel power is needed and in this case diesel power is a good and necessary investment.
When is diesel power necessary?
I’d love to hear your experience.
If you have switched between gas and diesel power.
What was your experience?
If you were to start over would you buy a gasser or diesel?
Let us know in the comments below.
Time plays a role in almost every decision. And some decisions define your attitude about time.
John Cale
We had home built RVs when I was a kid. Started with a pop up tent camper made from an 8 person tent, plywood & an axle. Then a 1960’s bread truck converted to a MH. Finally a 28′ Spartan mobile home converted w/a 1968 Toronado drivetrain attached to the front. This one was the first thing I drove at 13 years old.
As an adult since 2002 a 1997 Tropical Class A 36′, 2006 31′ 5th wheel, 42.5′ toy hauler and finally a 46′ 2001 Newell Motor Coach.
The Newell is our retirement RV we will travel the US in. It lakes for nothing for comfort. It is more expensive to maintain and fix when things go wrong (they always will) but I can keep her going. I do as much of the work as I can.
There is no substitute for experience and the skills you learn along the way. I agree, Newell builds a fantastic coach.