Gas vs Diesel: Seven Important Truths About RV Fuels

Which is better for you, gas vs diesel for your RV? That’s one of the biggest questions RV buyers need to decide.

It’s an important question to ask and answer before buying an RV.

That’s why it was a no-brainer to include a discussion on the topic in our book “RV Buying Secrets.”

“RV Buying Secrets” is a 70-page downloadable digital guide to help you understand the nuances that come with purchasing an RV including where to save thousands of dollars in the buying process, what questions to ask dealers, or how to understand your warranty and what it covers.

1. Gas vs Diesel: A Primer

For those who might not know the difference between the fuels, it’s worth spending a little time talking about how the two vary from each other.

Per the Universal Technical Institute, both gas and diesel engines “are internal combustion engines that convert chemical energy into mechanical energy. The mechanical energy moves pistons up and down inside cylinders, which creates a rotary motion that turns the wheels of a car forward.

Both types of engines convert fuel into energy via a series of small explosions or combustions. The engines have their differences as well.

One of the most important differences between gas and diesel engines is the thermal efficiency of diesel engines, which refers to the work that can be expected to be produced by the fuel put into the engine. As UTI reports, a diesel engine is about 20% more thermal efficient than a gas engine. That means a 20% increase in fuel economy. 

Additionally, diesel engines run at a much slower RPM (revolutions per minute) than a gas engine (see image), therefore there is less wear and tear and the life cycle of the engine is longer. 

Further, increased thermal efficiency also translates to more power and torque. A diesel engine’s high torque application is very beneficial for hauling heavy loads. 

Gas engines, on the other hand, deliver a much higher volatility point, but a lower flashpoint. A spark controls the combustion of a gas engine. According to UTI, “The fuel is compressed with fresh air and once the piston is on top of its stroke and the compression is at what the manufacturer wanted, a spark ignites the fuel and air mixture, which is what causes the engine to run.”

Diesel engines do not use a spark. Rather, they use what’s called a compression combustion engine, and there is a much higher compression ratio on a diesel engine than there is in a gas engine. The air-fuel mixture is squeezed so much that it explodes on its own. 

Essentially, a gasoline engine is a spark-fired combustion, and a diesel engine utilizes compression.

Now that you have some background on the differences between gas and diesel engines, let’s look at the pros and cons of each with regard to RVing.

2. Gas vs Diesel: Costs

The first consideration for many people shopping for a new RV is the price.

Simply put, does it fit your budget?

On the whole, diesel-powered RVs are much more expensive than gas-powered RVs.

First-time RV buyers often decide to go with a less expensive gas-powered RV rather than a diesel or luxury unit. But there are various degrees of quality within each type. Depending on what you are looking for, the best gas RVs on the market stack up against some lower quality diesel units.

However, if well maintained, diesel engines have a longer life than gasoline ones and can still perform reliably after extensive mileage. This means diesel-powered RVs tend to retain their value longer and have higher resale values than gas-powered RVs.

3. Gas vs Diesel: Mileage

As mentioned, above the second factor to take into consideration is the gas mileage.

After all, fuel is expensive and adds up over time.

Gas-powered RVs:

• Depending on chassis will have between 80-10 gallon tanks (Class A) and 20-30 gallon tanks (Class B)
• Average of 8-10 MPG (Class A), 10-14+ MPG (Class B and Class C)
• Widespread availability at all gas stations
• Cheaper than diesel
• Has an odor when burned, the smell can fill the cabin
• Has a shorter shelf life due to evaporation

Diesel-powered RVs:

• Depending on the chassis will have between 80-120 gallon tanks
• Average of 8-18 miles per gallon, with Class C’s and A RVs getting less, Class Bs and B+ RVs getting more
• More expensive than gas
• Available at most but not all gas stations
• Has better fuel efficiency, meaning less frequent refills at the gas pump
• Diesel burns cleaner than gas

(By the way, be sure to check out my short video report on the best apps to find the cheapest gas in the video below.)

4. Gas vs Diesel: Maintenance

Gas engines are much easier to maintain and repair compared with their diesel counterparts. If you have a general knowledge of gas engines, you can probably do a bulk of the repairs and maintenance yourself.

A downside of a gas engine is that it runs at higher RPMs. This means it will always be working harder than a diesel engine. Running at higher RPMs allows for a smoother, quieter ride with faster acceleration but more frequent upkeep is required.

Diesel RV engines are much more expensive to maintain and require specialized training to service. Diesel engines run at a lower RPM. This means slower acceleration and lower top speeds but there is less strain on the engine, and you can put in more miles between servicing.

A word of caution: To avoid a big maintenance bill, be sure to NOT accidentally put gasoline into a diesel tank, as one RV Lifestyle correspondent once did. 

5. Gas vs Diesel: Oil 

All engines require oil. Diesel-powered engines use a lot more oil than gas-powered engines but the oil only needs to be replaced once a year or every 15,000 miles. You’ll need to change the oil in a gas engine every six months.

In a gas engine, if you know how to change oil, you can do it yourself. Diesel oil changes are more complicated, so you’ll probably have to take it to a professional mechanic to do the work.

6. Gas vs Diesel: Speed and Towing Ability

Gas-powered engines typically have higher horsepower and less torque, so you can accelerate and maintain higher speeds. However, having less torque adds more strain on the engine while towing and climbing inclines.

Diesel-powered engines are designed for higher torque at lower speeds but are not as fast as gas engines. More torque means slower acceleration speeds but greater towing power and ease in steep inclines.

As you can see, there are some pros and cons to both styles of engines, but ultimately, the decision for you boils down to personal preference and your budget. 

Are you planning on carrying a “toad”? Do you frequent the Rockies and the Northwest’s mountains a lot? Having the power to climb hills with a load lends to diesel-powered engines.

Or are you planning on RVing without a “toad” and in relatively flatter areas such as New Mexico and Arizona? In that case, a gas-powered engine would work well for you.

7. Gas vs Diesel: The Bottom Line

Simply put, the bottom line on gas vs. diesel comes down to the bottom line. We like diesel-powered RVs for their better fuel economy and higher resale values opposed to gas-powered RVs.

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