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Last updated on August 30th, 2021

Diesel Generator Reviews & Buyers Guide

Diesel-powered generators are not the most common type available but they are a good alternative to conventional portable generators running on gasoline. Similar to cars, a generator running on diesel is more fuel-efficient which is just one of the perks of this alternative.

Best Diesel Generators

So, how does a diesel generator compare to a gas generator and how do you decide which one better meets your electrical needs? Here is a buying guide to help you make the wisest choice, including 3 of the best options that you can order today.

Top 3 Diesel Generators

1. Generac 6864 XD5000E

Generac 6864, 5000 Running Watts/5500 Starting Watts, Diesel Powered Portable Generator

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Though this Generac model has the lowest output in this top 3, it is by far still the best option available. The Generac 6864 is the most portable, provides clean energy, has a design fit for heavy duty use and offers an incredibly long run time.

First off, take a look at its fully welded 1.25” steel frame that acts as a protective outer frame for the industrial grade engine. The top has 3 separate bars, the middle one being an integrated lifting eye so that it can be moved easily on construction sites or purchase the wheel kit and instantly make it a highly portable design.

The engine is a 435cc from the Yanmar LW Series which features an air-cooled direct injection. Fueling this engine is a large 12 gallon diesel tank that can keep it running for a whopping 32.4 hours on a half load.

Besides running for a long time, this version also delivers a stable output that is close to the value of an inverter generator with only 5% Total Harmonic Distortion. This makes it safer to connect your sensitive electronic devices making this a suitable model for residential use, as well.

The control panel takes up about a quarter of one side but it is not cluttered. Here you will find the outlets (4x 20amp 120 volt, 1x 30amp 120 volt twist lock, 1x 30amp 120/240 volt twist lock), central circuit breaker, power switch and hour meter.

The battery is not integrated into the design so you will have to buy this separately if you want to make use of the electric start. However, there is a designated space for it so once it it setup you don’t have to worry about carrying 2 separate parts with you.

The downside is that it is not the most affordable option for its output since a gasoline-powered version in the 5000 watts range is likely only half or even a quarter of the price that this Generac XD5000E goes for. For this higher price tag you get a more efficient machine with lower maintenance costs and requirements so what is your priority?

Product Specs Details
Surge Power 5,500 watts
Running Power 5,000 watts
Tank Size 12 gallons
Run Time 32.4 hours at 50% load
Fuel Diesel
Noise Level N/A
Weight 254 lbs
Start Type Electric

Pros and Cons

PROs
  • Portable Design
  • Extremely Long Run Time
CONs
  • Battery Not Included
Generac 6864, 5000 Running Watts/5500 Starting Watts, Diesel Powered Portable Generator
  • Durable, fully welded 1 1/4" steel frame
  • Yanmar LW Series 435cc air-cooled direct injection, industrial-grade diesel engine

2. Cummins Onan Quiet Series RV QD10000

Cummins Onan Quiet Series Diesel RV Generator - 10 kW, Model Number 10HDKCA-11506

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Specifically designed for RVs, this is a powerful diesel generator that can handle running 3 AC units at the same time. Because of its 10,000 watts surge power and 8000 watts continuous power, this is also a suitable model as a home standby generator.

There is no fuel tank inside the casing so you will have to connect a separate fuel tank to get the engine running. Keep in mind that it uses up 0.43 gallons of diesel per hour when running a 50% load.

One of the best aspects of this model is that it is technologically advanced with a computer-controlled variable speed, pure sine wave output and a microprocessor that can self-analyze for any issues and troubleshoot. These features provide you with a low maintenance and high performance diesel generator.

The manufacturer has taken care to include several noise canceling elements such as a casing, muffler and enclosed cooling system, which brings the rated noise level down to 70 decibels, meeting the US National Park sound requirements. This product also fully complies to EPA and CARB regulations so you can power your RV in any US state.

Where an electrical start is the standard for diesel generators, this model takes it one step further with a remote start. The package includes a key fob so that you can start the engine from a distance which comes in handy when you are on the other side of the RV.

The biggest disadvantage is that it is not portable in the slightest. Weighing over 750 pounds without any tires or pulling handles integrated into the design, this is not a machine meant for mobile use.

This is a great off-grid power source if you are planning on an epic road trip in your RV or as an emergency standby generator for your home. It has a high output and low total harmonic distortion making it the smarter choice for connecting sensitive devices.

Product Specs Details
Surge Power 10,000 watts
Running Power 8,000 watts
Tank Size N/A
Run Time N/A
Fuel Diesel
Noise Level 70 dB
Weight 767 lbs
Start Type Remote

Pros and Cons

PROs
  • Remote Start
  • High Pure Sine Wave Output
CONs
  • Not Portable
Cummins Onan Quiet Series Diesel RV Generator - 10 kW, Model Number 10HDKCA-11506
  • Runs 3 rooftop air conditioners
  • Quieter than National Park Service sound level requirements

3. Power Products Sigma 7000W

The Sigma by Power Products has slightly more capacity than the Generac 6864. It has 7000 watts surge power and 5500 watts continuous power which is enough to run several air-conditioning units and the main household appliances such as the refrigerator and freezer, water pump or electric stove.

The control panel looks quite elaborate at first glance but once you take a closer look you will realize it is all pretty straight forward. There are 4 power outlets; 2x 20amp 120 volt, 1x 30amp 120 volt twist lock and a second twist lock that you can switch between 120 volts and 240 volts.

Other features on the control panel are the low oil warning light, fuel gauge and volt meter. It has an internal fuel tank with a 4 gallon capacity but you can also connect to an external larger fuel tank for a longer run time.

Power Products states it has a run time of 8 hours on a half load which is decent for its output. However, if you need this machine to run overnight it might be a smart idea to make use of that external fuel tank.

This giant yellow beast comes in at 363 pounds but Power Products has included wheels and a pulling handle so that it can still be moved (even though you’ll likely need 2 people pulling for it to budge). On the other hand, being heavier and larger than its gas-powered counterpart is a common downside for diesel generators.

Surprisingly, the Sigma is one of the quieter models with a rated noise level of 68 decibels. Diesel engines are known for being louder so this reasonable noise level for the amount of power provided is a welcome benefit of this budget product.

Overall, this is straightforward product but quite a heavy diesel model which might explain the lower price compared to similar designs. If budget is the most important factor then choose the Sigma but do note that you will be foregoing portability and advanced features.

Product Specs Details
Surge Power 7,000 watts
Running Power 5,500 watts
Tank Size 4 gallons
Run Time 8 hours at 50% load
Fuel Diesel
Noise Level 68 dB
Weight 363 lbs
Start Type Electric

Pros and Cons

PROs
  • Affordable Given the Output
  • Wheels Come Installed
CONs
  • No “High-Tech” Special Features (can be a pro or con really)

How Do Diesel Powered Generators Work?

The mechanics of a diesel engine is different to one fueled by gasoline. In a diesel engine, fuel and air is introduced into the engine simultaneously which creates a combustion point at a higher temperature compared to gasoline.

This higher combustion point is what makes diesel generators more fuel efficient. There is a compression ratio of 14:1 up to 25:1 while with gas there is a maximum compression ratio of 12:1.

Both types are considered internal combustion engines because they both burn a fuel. However, what sets of the burning in a gasoline engine is a spark or spark ignition while a diesel engine relies solely on the extreme compression of air with the fuel, also called a compression-ignition.

Advantages & Disadvantages

Advantages

These are the main reasons why you should a diesel generator over one running on gasoline.

Greater Fuel Efficiency: As mentioned, diesel-powered generators are more fuel efficient because diesel has a higher combustion temperature. Fuel efficiency results in several other benefits such as a longer run time and lower running costs.

Longer Run Time: It is not only the fuel efficiency that allows for a longer run time. Diesel engines are also sturdier so they can handle running for a longer period of time without overworking the engine compared to a gasoline engine.

Another element related to a long run time is the external fuel tank. Depending on the model, you can attach a larger external fuel tank to keep the machine running longer.

Heavy-Duty Design: As mentioned, the engine is better suited for long continuous work but most of the frames and casings are also designed for heavy duty use. Thus, both the exterior and engine ensure that this generator type is durable enough for long periods of continuous use.

Lower Running Costs: Several factors lead to an overall lower running costs for diesel generators. These factors are the fuel efficiency and in some cases lower cost of fuel depending on your area.

Safer: There are several reasons why diesel generators are considered safer than gasoline-powered models. The first reason is that it is less flammable, even when compared to propane, so you have less risk of a fire caused by leaking fuel.

The second reason is related to the mechanics. Since there is no spark plug, there is less chance of accidental combustion.

Less Chance of Breaking Down: The mechanics are simpler thanks to the absence of a spark plug and carburetor. A more simplified mechanism also means that less can go wrong and so it is less likely to break down while working.

Low Maintenance: Another benefit of simpler mechanics is that there are fewer elements that require routine maintenance. This not only cuts down the maintenance time but also cuts down the maintenance costs.

Disadvantages

Despite its many advantages, a diesel generator is not a magical machine and every product has its disadvantages. These are the biggest downsides of this type of generator.

Bigger Initial Investment: Overall, a diesel generator is more expensive compared to a gas-powered generator. It is a newer technology but it also has a longer lifespan which is why it often has a higher price tag compared to a different generator type with the same output.

Fewer Options: There are fewer diesel-powered models available on the market today. With this choice limitation you might not find the correct size, portability and capacity for your electrical needs.

Bigger Size: In general, diesel generators are larger which makes them heavier and less portable. This limits the number of uses that it is appropriate for.

Less Effective in Cold Weather: Colder temperatures make it more difficult to reach the peak temperature for combustion so a diesel engine is more difficult to get started in freezing temperatures. However, this issue can be solved by installing glow plugs and heating elements.

Noise: The noise levels are generally higher so make sure that you choose a model that has soundproofing or noise canceling design elements. Fortunately, this has become a priority for many manufacturers.

Conclusion

So, the most important question to answer is; are diesel generators better than gasoline-powered generators? There is no simple answer because it depends on the purpose.

For extended heavy duty use, a diesel generator is the better option because it is more fuel efficient, durable and safe. However, this type loses in portability, noise and low budget needs.

Last update on 2021-09-24 / Affiliate links / Images from Amazon Product Advertising API