The 3 Best Diesel Generators – Reviews and Buying Guide

Generac 6864

Generators are powerful machines capable of supplying and distributing power to all the electrical appliances you need at the same time, depending on the power rating and the number of electrical appliances in your home. You can choose from several fuels to power these generators, such as diesel, natural gas and liquid propane. Diesel generators offer the same power output, but they outperform other generator models in terms of ease of maintenance and durability.

Diesel generators are quite rare, but the features to consider are the same as for other types of generators. These include engine and fuel consumption, which is a check on cost-effectiveness and the amount of fuel consumed per minute. Another important factor to consider is the power output of a diesel generator; the power output determines the number of electrical devices a machine can power based on its power rating. Last but not least is the tank volume, which determines how much fuel the diesel engine can take in at one time. The higher the tank volume, the longer it takes for the fuel to run out.

We spent three dozen hours researching diesel generators to come up with the three best models available online. Below you’ll find a summary table of the top three products, followed by a more detailed review of each model, with its pros and cons. We’ve also summarised everything you need to know about diesel generators in the buying guide below.

DuroStar DS7000Q

The DuroStar DS7000Q is an ideal diesel generator for almost any situation you encounter, from emergency power outages in your home to the high demand for power on farms, maintenance and construction sites, etc.

The diesel generator is powered by a single-cylinder, four-stroke, air-cooled diesel engine that uses a highly advanced fuel injection system that reduces fuel consumption rates. It has a peak power of 6,000 W and a constant power of 5,500 W. It comes in a fully enclosed frame and has a soundproofing function as well as a super quiet silencer. These features help the DuroStar DS7000Q diesel generator to reduce noise and run smoothly.

DuroStar DS7000Q

The electrical part of the generator is equipped with a durable and reliable alternator with an automatic voltage regulator to reduce or increase an anomaly in the generated power. The power panel contains the main controls, including a start switch, voltmeter and circuit breaker. It offers two three-pronged 120-volt, 20-amp outlets (with GFCI) to power all your appliances, as well as two twist-lock outlets for power tools: a three-pronged 120-volt, 30-amp outlet, and a four-pronged 120/240-volt, 30-amp outlet.

  • The generator comes with a one-year limited warranty.
  • Single cylinder, direct injection, 4-stroke, 3600 RPM diesel engine.
  • 6,000 W
  • Rated power
  •   5,500 W
  • 37.8 x 22 x 30.3 inches
  • 305 pounds
  • 3.83 gal.
  • 12 hours run time on 1/2 charge
  • Limited to 1 year
  • Remote start and/or electric start, automatic oil alert shut-off, voltmeter, circuit breakers, low fuel indicator.

Generac 6864

Probably the best thing about this diesel generator is that it is more efficient and offers consumers a long service life. It is equipped with the Yanmar LW Series 435cc air-cooled, direct injection, EPA Tier IV, industrial grade engine. It has a total harmonic distortion of less than 6% for clean and smooth operation of electronic devices, tools and sensitive applications.

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The generator has a 12-gallon fuel tank with a fuel gauge that provides a long run time of 32.4 hours on 1/2 load. The decompression lever allows for easier starting in cold weather. It also has a feature called “low oil pressure shutdown” that allows the system to shut down when oil pressure is low, automatically protecting the engine from damage.

Generac 6864

The generator also comes with a fuel priming bulb that allows faster starts when the fuel tank is empty. The generator itself is very durable and welded with a steel frame. It has an integrated lifting ring that makes it easy to transport and ensures safety where it is placed.

A great advantage of this generator is that its 120/240V selector switch provides full 120V power, or you can switch it to 240V if you need it. The one-touch electric start allows for trouble-free starting, even though the battery is not included. Finally, it has an hour meter and a maintenance reset function that allows you to track usage and monitor maintenance cycles. It also comes with an additional wired power source.

Yanmar LW Series 435cc air-cooled direct injection industrial diesel engine, 3600 RPM

Generac 6864
  • 5,500 W
  • 5,000 W
  • 33.1 x 22.5 x 25.6 inches
  • 254 lbs
  • 12 gal.
  • 32.4 hours run time on 1/2 charge
  • Limited to 2 years
  • Durable 1 1/4″ fully welded steel frame.


A powerful generator such as this is a rotating field of the liquid discharge generator type. It has two poles and a self-excitation frequency measured in Hertz (Hz) of about 60Hz. It has an output power measured in KiloWatts(kW) of 5.5 or 5500W. The AC voltage, measured in Volts(V), is between 110V and 220V.

Its operation is very good due to the speed at which the engine runs; it boasts an engine speed of about 3,600 rpm. It also has a direct injection system, as the engine is vertically aligned, and a four-stroke, air-cooled diesel engine.


The starting system, which is the electric system, is equipped with a battery for ignition. The generator has a single-phase power factor of 1. The excitation system is a controlled self-excitation. The coupling design is a shaft-coupled starting motor. The lubricating oil is zero degrees in summer or negative twenty degrees in winter. A standard fuel gauge with voltmeter, AC circuit breaker, motor switch, 1V/8.3A DC output, low oil warning, AC plug with handle and wheel are supplied with the purchase.

  • SIGMA 7000W Engine
  •  direct injection, vertical, four cycle, air cooled diesel, 3600 RPM
  • Peak power
  •  7,000W Rated power
  •  5,500W Dimensions
  •   37.5 x 22.5 x 30 inches
  • Weight 385 lbs
  • Tank volume 3.96 gal.
  • Run time 4 hours run time on 1/2 charge
  • Warranty not specified

Durable, fully welded 1-1/4″ steel frame, electric start with battery.

Advantages and disadvantages of diesel generators

The maintenance costs associated with the use of diesel generators are very low. This is due to the fact that diesel generators do not have spark plugs or carburetors. This means that there are no spark plugs to replace and no carburetors to rebuild. The main maintenance required for the diesel generator is the oil change and, if done regularly, your diesel generator will last for a very long time with no major maintenance required.

It has also been observed that diesel generators tend to last longer than petrol generators when doing the same amount of work. They perform the same workload and do not consume as much fuel as gas generators. The fuel itself is also cheaper than gasoline and propane.

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In terms of service life, the diesel generator is much more durable than the gasoline generator. A typical gasoline generator will last about 1000 hours or more. In contrast, the diesel generator will last an average of 30,000 hours without needing a major overhaul. The diesel generator is built to withstand pressure and operates at half the speed of gasoline generators that are built primarily for intermittent use.

Comparison of diesel and petrol generators

Diesel fuel is also much easier to store than petrol. It is flammable, but the risk is not as great as that of petrol, which can be explosive. The exhaust from the diesel engine is actually more visible, which is considered one of the main disadvantages of diesel as a fuel. However, if the diesel generator is properly maintained, there is no need to worry, as the exhaust will only be visible when the generator is subjected to significant load changes.

Diesel can be very noisy, and this is considered a major drawback of the diesel system. This is usually one of the reasons why owners tend to opt for petrol generators. The petrol generator is much quieter than the diesel generator, so there is no need to install it far from houses. There are now other options, such as soundproof enclosures, that can help solve this problem.

There is also the initial cost of installing a diesel generator. This cost is generally somewhat higher than that of the petrol generator. However, it can be seen that the costs of the diesel generator, compared over a few years, are much lower than those of the petrol generator.

Diesel Generators

The choice of a diesel or petrol generator can be assessed in terms of use. If the generator is intended for intermittent use, a petrol generator may not be a bad buy, but overall, the diesel generator is considered more economical. The advantages of the diesel generator far outweigh the disadvantages, making it the best buy.

What should you look for in an ideal diesel generator?

As mentioned above, the main features of diesel generators are pretty much the same as those of other types of generators. Let’s look at them in more detail.

A powerful engine

The engine power of any diesel generator must be noted because the amount of load the engine can carry depends solely on the power generated by the engine. In most cases, when a particular diesel engine generates less power than required, it becomes very frustrating for the user and can lead to damage to the diesel generator. In most cases, when a particular diesel engine generates less power than necessary, it becomes very frustrating for the user and can lead to damage to the diesel generator. A four-stroke engine is the best one to consider as it allows smooth operation of the diesel generators.

Power output and fuel consumption

The power output refers to the amount of energy that can be supplied to the electrical appliances connected to the diesel generator. The higher the power output, the more machines or electrical devices can be used with the diesel generator. The power output is measured in watts, which makes it easy to see in the product descriptions of diesel generators. The fuel consumption of diesel generators varies from manufacturer to manufacturer, making it difficult to calculate a standard measurement, but in general, the fuel consumption of diesel generators determines the rate of diesel use during machine operation. The higher the load of a diesel generator, the higher the fuel consumption rate, because a very low load does not require too much fuel. The fuel injection system in the engine plays an important role in determining the fuel consumption level of a diesel generator.

Quiet operation

Many consumers value the quiet characteristic of a diesel generator, which makes it necessary in some way for diesel generators to be as quiet as possible during operation. Some diesel generators are equipped with a soundproofing feature through a muffler system that allows for little or no noise during operation. The DuroStar DS7000Q diesel generator is an example of this type of generator with silent operation.

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Safety for sensitive electronics

In power generators such as diesel generators, the reduction of peak currents, heat, emissions and core loss in engines is very important for the life of diesel generators. To achieve this, diesel generators are assigned a THD value after rigorous testing and measurement. Thus, for a diesel generator, a lower THD means more safety for the delicate electronics. A THD of less than 5% is best for diesel generators, and the DuroStar DS7000Q, GENERAC 6864, SIGMA 7000W have very low THDs.


The size of a diesel generator varies depending on the structure of the generator and the manufacturer. Know how much space you have before you buy a diesel generator so that you do not have space problems. The DuroStar DS7000Q and the SIGMA 7000W take up more space than the Generac 6864.


The warranty of the products depends on the manufacturer. The warranty allows you to return a given item to the place where you bought it if it has any defect during the warranty period. The warranty can last up to one year, or even longer in some cases.

Additional features

The extra features in a diesel generator are the special things included in the diesel generator by the manufacturer. The SIGMA 7000W comes with an extra feature that includes: durability, fully welded 1 1/4″ steel frame, electric start with battery. The DuroStar DS7000Q comes with an additional feature that includes: remote start and/or electric start, auto shutdown oil alert, voltmeter, circuit breakers, low fuel indicator. The Generac 6864 comes with an additional feature that includes: durability and a fully welded 1-1/4″ steel frame.

Our verdict

Overall, the DuroStar DS7000Q comes out on top because it has great features, isn’t too expensive and generates enough power. That’s why we ranked it as the best of all. The SIGMA 7000W gets an overall score of 8.7 with good enough specifications and features. Coupled with the fact that it’s cheap, it meets all the other areas where it doesn’t play too well. We made the SIGMA 7000W our budget choice. Finally, the Generac 6864 boasts an overall rating of 9.0 with high durability and a very long battery life of 32.4 hours on a half charge. However, its price does not make it affordable.

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