If you’re in the market for a new generator, it can be challenging to know which fuel source is right for your application

First, let’s discuss the pro’s of diesel generators: 

  • Very reliable, very durable
  • Engines produce low end torque for instantaneous heavy loads
  • Readily available fuel supply
  • Performs well in high ambient temps 

There’s a reason that diesel engines are the engine of choice for the commercial transportation industry. First and foremost, a diesel engine’s simplicity of design means fewer parts to break. This leads to increased reliability and longevity. There are diesel generators that were manufactured in the 50’s and 60’s that are still running today. The same low end torque that allows an 80,000lbs commercial vehicle to climb a mountain allows these generators to take on a full load almost instantaneously. To put it mildly, these engines perform amazingly under load. 

Like a commercial motor vehicle, diesel generators are great portable options that perform well over the road. The vast fuel network that exists for commercial motor vehicles and farm implements ensure you’re never too far from fuel. Despite it’s higher energy density, diesel is also far less flammable than options like gasoline, natural gas (NG) or liquid propane (LP). This is an important safety consideration with portable power supplies, and one of the reasons you see so many diesel generators on the road today. 

Did I mention that they require less maintenance than their gasoline, NG and LP counterparts? Some diesel generators can run 3x longer than a gasoline/NG/LP engine before they need a service. We have found it a good practice to use synthetic oils specially formulated to avoid viscosity breakdown at the higher temperatures found in many diesel engines. 

While powerful and portable, diesel generators are not without their issues:

  • Not ideal for extremely cold weather
  • Louder and dirtier than other options
  • Incomplete combustion (soot)
  • Fuel contamination
  • Wet Stacking

Because diesel engines rely on heat and pressure to ignite their fuel, low ambient air temperatures can have an adverse impact on start up and power (at least until the engine gets up to temperature). Cold weather can also impact the fuel itself. Any water in the fuel tank can ice up and the wax in the fuel also separates creating a condition known as “gelling” which can plug your fuel filter and prevent proper operation. For this reason, diesel generators are not the ideal choice for outdoor placement (think a metal encasement near a cell tower in an open field). Both the engine and the fuel will do better if given dedicated room inside your building.  

While modern diesel generators are cleaner and quieter than ever, many of the late model/off-road engines used in generators are behind the curve when it comes to emissions, cleanliness and noise levels. This is due, in part, to the fact that emission controls on an engine sacrifice a bit of reliability for cleaner, quieter, higher temperature exhaust. As with any system, the more parts you have, the more opportunities you have for something to go wrong. Modern diesel engines also require the addition of DEF, meaning you have to have an additional tank to store the additive. 

Because it is more viscous, diesel fuel is also more prone to picking up contaminants. This can range from water to soot. As previously discussed, this can clog filters and cause a loss of power and difficulty at start up at the most inopportune time (the reason you have a generator in the first place).

Lastly, wet stacking occurs when the load a generator is operating under is too small. Because diesel engines rely on heat and pressure for combustion, matching the power of the engine with the size of the load is absolutely critical. This is not a case where bigger is better. This can create challenges when it comes to scalability. If you want to buy a larger generator to facilitate future growth, know that it may be necessary to add a load bank (think giant toaster oven) that provides the additional load needed for optimal engine operation. This is in stark contrast with a gasoline, NG or LP generator which can actually perform better under lighter loads.

The bottom line is this: When long term reliability, portability or service to remote locations are key considerations, few options perform better than diesel generators.