Diesel Vs. Gas Marine Engine Comparison

New boat buyers will face several questions when trying to find their perfect boat. Outboard or sterndrive? Aluminum or fiberglass? And when considering power options they will inevitably get to the question: diesel or gas? This article is intended to help educate new buyers on the pros and cons of both options.

The diesel motor’s claim to fame is fuel efficiency and longevity. Due to its torque the diesel has the ability to push a large load at a relatively low RPM and thus maintain a lower fuel flow rate and theoretically last longer.  These attributes have one major trade off, the up front purchase price. When you consider the premium on powering your boat with  diesel motor(s), and the higher repair and maintenance costs, how long will it take to re-coup that money in fuel savings? And may those savings be outsripped by repair costs.  It is often only the commercial user who will use his boat enough to make diesel pay in the long run, or a recreational boater who is planning on taking the boat for long trips, so are going to have a lot of fuel consumption, that it makes economical sense to go diesel. For the weekend warrior or fisherman who puts more hours on a kicker motor than his main power it might not actually save you any money. 

Diesel Pros:

• Fuel efficiency

• Usually lower $/litre at the pump

• Potentially longer life expectancy  

Diesel Cons:

• Expensive purchase price

• Expensive maintenance and repair costs

• Noisy

• Diesel exhaust odor is more noticable and unpleasant than gas exhaust, most noticeable at low vessel speeds

The good old gas sterndrive is the most common method of powering pleaseurecraft below 30 feet long. While not as fuel efficient as their diesel counterparts, they are much cheaper to purchase and maintain. Serviceability is arguably better for gas motors as almost every marine mechanic has some gas experience while a good outboard or diesel tech is becoming harder and harder to find. The gas motor is the leader in high performance applications due to their ability to run at higher revolutions and the old GM blocks used by both Mercury Marine and Volvo Penta up until recently have been around for so long that there is no shortage of  affordable parts to maintain them. While they typically will not last as long as a diesel - most gas engines can be expected to run for 2000 hours before major repairs are required - repowering them is far cheaper than doing so with a diesel motor. The modern gas motors can be equipped with catalytic converters making them the cleanest running motors over both diesel and outboard. 

Gas Pros:

• Significantly lower purchase price

• Lower maintenance and repair costs

• More mechanics around who can work on them and better parts availablity

• Greater variety of aftermarket parts

• Easily tuned for higher performance

• Greater power to weight ratio than diesel

• Cleaner burning 

Gas Cons:

• Less fuel efficient than diesel

• Potentially lower life expectancy