About Engines
Generators provide reliable electric power for numerous applications, whether it’s running tools on an off-grid construction site or operating a household’s microwave during a power outage. The engine in a towable, stationary, power plant, marine, home standby, compact recreational, or portable generator converts fuel into mechanical energy that the unit’s alternator then converts into electric energy.

2025 Caterpillar 3561B
Generator engines differ in design, size, capacity, and fuel type. For example, while a compact recreational generator generally runs on gasoline, a power plant generator may utilize diesel, coal, natural gas, or another fuel type. Keeping the following considerations in mind when buying a generator can help.
The Size Of The Engine
A football fan using a small generator to power an HDTV at a tailgate party has far different power requirements than a factory owner running his operation with a power plant generator. The engine’s size impacts the generator’s power output. Larger engines typically generate more power, have more cylinders, and may require more effective cooling systems.
Fuel Type Requirements
There are generators on the market with engines that operate on various fuel types. Each offers advantages and disadvantages related to cost, efficiency, environmental conditions, and other factors.
Gas
- Widely available
- Cheaper up front but less fuel-efficient vs. diesel
- Good cold-weather starting capability
- Commonly used in portable and compact recreational generators
Diesel
- Longer run times vs. gas
- Typically longer-lasting engines
- Lower risk of flammability vs. gas
- Often used in towable, stationary, power plant, and marine generators
Propane
- Burns cleanly, lower emissions
- Reliable starting in cold weather
- Lower energy density vs. diesel
- Used in stationary, towable, home standby, and portable generators
Natural Gas
- Produces very low emissions
- Favorable fuel costs
- Requires natural gas pipeline, so not much portability
- Used in stationary, towable, power plant, home standby, and portable generators
Additional Considerations For Generator Engines
Along with engine size and fuel type, consider the following when choosing a generator engine.
- Working environment. Differing applications may require specific engine characteristics; for example, a marine generator engine must withstand extreme heat, dampness, and other taxing conditions
- Manufacturer. Caterpillar, Cummins, and Kubota are just some of the many reputable generator engine manufacturers
- Maintenance. Determine the cost and level of ongoing engine maintenance required
- Availability. Note the availability and cost of replacement parts
- Starting method. Match the generator’s electric or recoil starting mechanism to your preference
Where To Buy & Finance Generator Engines
Explore PowerSystemsToday.com to find new and used generator engines for sale from industry-leading manufacturers such as Bobcat, Caterpillar, Cummins, Deutz, Isuzu, Komatsu, Kubota, and Perkins. The site offers for-sale listings for a wide variety of diesel, natural gas, 4-cylinder, and 6-cylinder engines, plus complete generator sets in natural gas, diesel, and other models.
If you have already chosen the best engine for your needs, explore your generator and power systems with CurrencyFinance.