5 Best Diesel Generators: Fuel Efficient Powerful Machines

Power outages can be frustrating and irritating. So, you must have a proper backup power solution for them. You can invest in any generator, but buying a diesel generator is the best way to deal with frequent power failures.

Diesel generators are cost-effective and need less maintenance as compared to other generators. Also, they consume less fuel during operation to provide higher runtime. Moreover, they have a long lifespan.

So, always try to buy a diesel generator for both indoor and outdoor usage.

Diesel Generator Reviews





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Firman SDG5500CLE Diesel Generator

  • 418cc, 9.4HP, 4-stroke diesel engine

  • recoil and electric start systems

  • 6.5 hours runtime at 50%

Yamaha EDL1100E Diesel Generator

  • Oil/restart indicator light

  • Electric start system

  • 8.5 gallons fuel tank

DuroStar DS7000Q Diesel Generator

  • 418cc, 4-stroke, single-cylinder diesel engine

  • maintenance-free brushless alternator

  • 3.8-gallon diesel tank

Generac 6864 Diesel Generator

  • industrial-grade 435cc, 4-stroke diesel engine

  • Recoil/Electric start mechanisms

  • huge 12-gallon diesel tank

Generac RD01525ADAL Diesel Generator

  • Mitsubishi 2.5L diesel engine

  • 95 gallons fuel tank

  • low oil shutdown

1. Firman SDG5500CLE Diesel Generator – Overall Best

Firman diesel portable generator

Design: Firman SDG5500CLE is an open frame diesel generator. It is a portable machine that comes with a 4-wheel transport kit. Users can easily move from one side to the other.

Engine: Its 418cc, 9.4HP, 4-stroke, the single-cylinder diesel engine produces decent output power. It has a direct injection fuel system that injects the fuel directly into the combustion chamber, unlike the indirect injection fuel systems. This boots the fuel economy.

Also, it has an air-cooled system that uses air to keep the engine cool during operation.

Alternator: The SDG5500LE has a brushless alternator. It uses a motor, free of carbon brushes, to create electricity. Two sets of rotors are used instead of the carbon brushes that spin together to create and transfer electricity.

Starting Mechanism: It is featured with both recoil and electric start systems. If it is hard for you to pull-start the generator, use the electric start mechanism.

Power Wattage: The output power it produces is 5000 starting watts and 4500 running watts. With this power, you can easily run multiple appliances or tools at once.

Fuel Tank Size and Runtime: The fuel tank size of Firman SDG5500LE is 3.3 gallons. On a full tank, it can run up to 6.5 hours.

Volume Level: It is a noisy generator with a decibel rating of 85 dBA. So, it is suggested to keep it far away from you to get as little noise as possible.

Power Receptacles: The power panel of this diesel generator has two AC outlets and one 12 Volt DC outlet.

Other Features: Other features include a voltmeter, low-oil alert system, engine switch, and circuit breakers.

The voltmeter shows you the power output, and the low-oil alert system turns on when the oil level goes down the minimum level.

Weight: This diesel generator is heavy, weighing 231 pounds. But thanks to its durable wheels that make it easy to move around.

Safety: Low-oil level safety feature protects your diesel engine from damage caused by running on low oil.

My Opinion:

Pros: Firman SDG5500CLE is a reliable diesel generator that produces enough output power to run your multiple appliances and tools. It has a brushless alternator, electric start system, and a low-oil shutdown feature. Also, it is a fuel-efficient generator.

Cons: It is loud.

2. Yamaha EDL1100E Diesel Generator – Heaviest Portable Diesel Generator

Yamaha High-powered portable generator

Design: Yamaha EDL1100E is also an open frame diesel generator. It is tough, durable, and features a 4-wheel transportation kit for easy mobility.

Engine: It is powered by a reliable 719cc, 4-stroke diesel engine featuring a liquid-cooled cooling system.

Alternator: It has a brushless alternator that is more efficient than a brushed alternator. Also, it needs less maintenance.

Starting Mechanism: Electric start system makes it easy for the users to turn on the generator.

Power Wattage: Yamaha EDL1100E is a powerful diesel generator that produces 8800 peak watts and 8000 running watts. This output power makes it an ideal choice for contractors and homeowners.

Fuel Tank Size and Runtime: Its fuel tank can store up to 8.5 gallons of diesel that can operate your generator up to 8.8 hours.

Volume Level: Its noise level (76 dBA) is lower than Firman SDG5500CLE.

Power Receptacles: Power your appliances and tools through multiple AC power outlets.

Other Features: Other than power outlets, it has an oil warning system, voltmeter, hour meter, and a fuel level indicator.

The fuel level indicator tells users how much fuel is left in the tank, and the hour meter shows the total runtime of the generator.

Weight: It is quite a heavy generator weighing 580 pounds.

Safety: Overload protection, low-oil shutdown, and an automatic voltage regulator are included in its safety features.

Overloading causes overheating in the generator’s stator winding, and the overload protection prevents that overheating. The automatic voltage regulator automatically controls the generator voltage and keeps it to a constant level to prevent damages to the electrical equipment.

My Opinion:

Pros: Yamaha EDL1100E is a powerful diesel-powered generator. It has an efficient brushless alternator, higher fuel storing capacity, and multiple safety features.

Cons: It is quite a heavy unit.


3. DuroStar DS7000Q Diesel Generator – Best Closed Frame Generator

DuroStar closed frame diesel generator

Design: DuroStar DS7000Q is a closed-frame diesel-powered generator. Its all-metal construction makes it sturdy and durable. Also, it has durable tires and a lifting eye so that users can transport it easily.

Engine: It is equipped with a 418cc, 4-stroke, single-cylinder diesel engine featuring an air-cooled cooling system. It has an advanced direct fuel injection system that consumes less fuel as compared to indirect injection fuel systems.

Alternator: It also features a maintenance-free brushless alternator that helps save money.

Starting Mechanism: The best thing about this diesel generator is that it comes with both electric and remote start systems.

Power Wattage: DuroStar DS7000Q can generate 6000 surge watts and 5500 rated watts. This power output is enough to run multiple appliances and tools simultaneously.

Fuel Tank Size and Runtime: Its 3.8-gallon diesel tank can run your generator up to 12 hours at 50% load.

Volume Level: It features a super quiet muffler to reduce the engine noise, but still, its noise level (78 dBA) is slightly higher than Yamaha EDL1100E.

Power Receptacles: The power panel of DuroStar DS7000Q has a variety of outlets, including two 120 Volt 20 Ampere receptacles, one 120 Volt 30 Ampere receptacle, and one 120/240 Volt 30 Ampere receptacle.

Other Features: It also has a voltmeter, power indicator, and an oil alert lamp.

Weight: DuroStar DS7000Q is quite lighter in weight (305 pounds) than Yamaha EDL1100E.

Safety: The automatic low-oil shutdown feature turns off the engine when it senses the remaining oil is insufficient for the engine to run. Also, a built-in spark arrestor blocks the sparks from coming out of the engine to protect the generator and its surroundings.

Emissions: It is an EPA (Environmental Protection Agency) certified unit. It means you can use it in 49 states of the US but not in California.

My Opinion:

Pros: DuroStar DS7000Q is a durable unit having sturdy construction. It is approved from EPA, features a brushless alternator, and offers a good runtime.

Cons: It has a small fuel tank.

4. Generac 6864 Diesel Generator – With True Power Technology

Generac Diesel Powered Generator

Design: This Generac 6864 is an open frame generator that runs on diesel. It has a 1-1/4” steel frame for strength and durability.

Engine: It comes with an industrial-grade 435cc, 4-stroke, vertical cylinder diesel engine featuring a direct injection fuel system.

Starting Mechanism: Electric start system with a recoil backup makes this generator easy to operate.

Power Wattage: The peak power it produces is 5500 watts, and its rated power is 5000 watts.

True Power Technology: The best feature of this diesel generator is True Power Technology. You can run not only your home appliances and tools but also power your sensitive electronics through this generator. Its Total Harmonic Distortion is less than 5%, which is ideal to power vulnerable electronic items.

Fuel Tank Size and Runtime: It features a huge 12-gallon diesel tank, which provides a long runtime of 32.4 hours at half load.

Power Receptacles: Generac 6864 has four 120 Volt 20 Ampere receptacles, one 120 Volt 30 Ampere receptacle, and one 120/240 Volt 30 Ampere receptacle.

Other Features: A voltage selector switch that allows you to either operate your unit at 120 Volts or both 120 Volts and 240 Volts at the same time. Also, its power panel has an engine switch, main breaker, and an hour meter for tracking maintenance intervals.

Weight: The weight of this unit is 254 pounds. Its open-frame design helps you to move it from one place to another. Also, there is a lifting eye for easy transportation.

Safety: Low-oil shutdown turns off the engine to prevent damage.

My Opinion:

Pros: Generac 6864 is a durable diesel-powered generator that comes with a massive fuel tank. It comes with a True Power Technology and offers excellent runtime. Also, its low-oil shutdown feature safeguards the generator.

Cons: It doesn’t run without a battery.

5. Generac RD01525ADAL 15kW Standby Diesel Generator – Best for Whole House Needs

Generac standby diesel generator

Design: Generac RD01525 is a standby diesel generator. It is not a portable generator. It is best for backup power for homes, offices, and other commercial premises.

Engine and Power Output: The machine uses a Mitsubishi 2.5L in-line 4 cylinder diesel engine capable of producing 15K watts. The best thing about standby generators is that their starting and running wattage is the same. This machine offers 15000 rated watts. It can be run on 120/240 single-phase voltage.

Starting Mechanism: It is an auto-start machine. When the utility power goes out, the sensors automatically turn on the machine to bring back the power. You will just notice a 1-2 second blackout.

Fuel Tank Size and Runtime: The tank is huge and can hold up to 95 gallons of fuel. The fuel consumption is 0.85 gallons per hour at full load. One full tank will last for a very long time.

Weight and Dimensions: The unit measures 81 x 31 x 65 inches and weighs 1757 pounds. Standby units are big. Make sure to check out you have ample space for installation.

Safety: You get low oil shutdown, overload protection, and surge voltage protection. The machine is enclosed in a corrosion-resistant aluminum enclosure which makes it safe for coastal and salt-water environments.

Also see: Best Quiet Generators: Don’t let noise cause high stress in you

Other Features: You get mobile link connectivity to monitor the operating condition of the machine from anywhere in the world. You can check the current condition and the maintenance schedule.

Warranty and Certifications: You get 5 years warranty, and this machine is approved by EPA and CARB to be used in all 50 states.

My Opinion:

Pros: It is an excellent machine for people who can’t afford downtime or need power at all times.

Cons: It is costly to buy, maintain and repair.

Buyer’s Guide

After going through the best available diesel-powered generators, it’s time to know which of the factors you should consider when buying a diesel generator.

Output and Power Needs

The most important thing to look at a generator is its output and your power needs. We don’t want you to end up with a too-small generator or an overly large one so that you have to deal with power issues later on. The best way to do this to calculate your power needs. You can do this by making a list of all the appliances you want to power during an outage and mention their starting and running wattages separately. To make this clear, we have given an example below.

Appliances Starting Wattage Running Wattage
Refrigerator 1400 300
1/2 HP Furnace 2350 875
TV 400 400
Lights 200 200
AC (2) 3600 2400
Total 7950 4175

In the table above, the starting wattage needed to fire up all the appliances at one time is 7950 watts. The running wattage is 4175 watts. If you are new to the field of generators, you would be tempted to buy a generator with a running wattage of 8000 watts. This is not the right choice. You need to buy a generator that can accommodate the running wattage of your appliances. All of the appliances above can be managed by a generator having a 4500 running wattage. It is best to leave a cushion of 200-300 watts to adjust any small additional appliances.

Buying a smaller generator has its perks. It will be less costly to buy. The running and maintenance costs are also less as compared to a large generator.

Generator Type

Before buying a diesel generator, first, make sure whether you need a standby generator or a portable generator.

A standby diesel generator is a permanent home backup power option that provides seamless power to your house. It automatically turns on when the utility power goes out and shuts down when the utility power comes back.

These standby generators are fully enclosed and provide clean power to run your appliances, tools, and electronics. But you cannot move them from one place to another. Also, you cannot install them by yourself; they need a professional to get installed.

On the other hand, portable diesel generators are easy to move around. You can either use them during power outages at home or power your tools at an off-grid construction site. But you need to turn them on manually.

Most of the portable diesel generators don’t produce clean power, but still, you can find the units having a THD rating of less than 5%. Also, they are easy to install without taking any help from a professional.

In our products list, we have only mentioned portable diesel generators because they are multi-purpose. But if you need a standby generator, you can go for it.

Control Panel

When it comes to standby models, you must look for a generator that gives you maximum control and information on the control panel. A control panel keeps the user aware of the working condition of the generator. It also tells you about fuel level, oil level, running hours, wattage is drawn, and other parameters. Some generators will also indicate when you need to change oil and air/oil filters.


Diesel generators with big fuel tanks give higher runtime like the Generac 6864 that gives up to 32.4 hours of runtime at 50% load on a 12-gallon tank. Some diesel generators come with an idle control feature that automatically changes the engine’s RPM when there is no load which helps save fuel. This results in a higher runtime. However, not all diesel generators are fuel-efficient, like the Yamaha EDL1100E.

Still, if we compare diesel generators with their gasoline-powered counterparts, diesel units are more fuel-efficient. They run longer on the same amount of fuel.

Noise Level

The higher the decibel rating (dBA) of a diesel generator, the higher will be the noise. And lower the decibel rating, the lower will be the noise level. So, always try to invest in a generator with a lower decibel rating to have a peaceful environment around you.

Safety Features

Automatic low-oil shutdown and overload protection (circuit breaker) are the common safety features that you will find in every portable diesel generator. Also, some units come with AVR (Automatic Voltage Regulator) and spark arrestor features that protect your generator and appliances in the best possible manner. 


If you are buying a portable diesel generator, look for features like wheels, carry handles, and a lifting hook. The quality and design of these features may vary from one model to another, but their presence makes the generator user-friendly.

Warranty and Certifications

Looking for a warranty and certifications is critical. Standby generators are difficult to maintain and costly to repair. Hence, it is better to look for a generator that comes with some sort of warranty. The industry standard is 1-3 years. Buying a generator with certifications ensures that your generator complies with all the safety standards.


When you want a high-end diesel generator with all the features, expect to pay a high price for it as well. Basic models are inexpensive but are limited in terms of features. You do not get an advanced control panel, safety features, and digital displays. If you plan to buy a standby generator, we suggest looking for a model with the best features and don’t compromise on the quality. What’s the benefit of saving a couple of hundred bucks when you have to pay thousands in maintenance/ repairs for the next 5-6 years?

Diesel vs. Propane vs. Gas Generators

Diesel generators are best when it comes to fuel efficiency. They will consume less fuel than gas or propane to provide you with the same power output. A propane engine will consume 3 times more fuel than a diesel generator to provide the same output. The reason is that diesel has the highest energy rating among the three. Diesel is the least flammable fuel among the three and also has a better shelf life than gasoline. Shelf life for propane is far greater than diesel. Because diesel generators don’t have carburetors or spark plugs, they need less maintenance. A diesel generator is the nosiest of the lot. However, recent advancements have made them quieter. The exhaust produced by diesel generators is not clean as compared to propane. Its exhaust is even worse than gasoline.


Why use diesel-powered generators?

There are various advantages of using diesel-powered generators. Some of them are listed below.

  • Diesel generators are more powerful than gasoline generators.
  • They are more fuel-efficient. Diesel generators use less fuel as compared to gasoline-powered generators, which results in higher runtime.
  • They are designed to be used for longer periods.
  • The life cycle of diesel engines is longer than gasoline engines.
  • Modern diesel generators need less maintenance as compared to gasoline generators because they don’t have carburetors and spark plugs.

Which generator is best to buy: Air-cooled or liquid-cooled?

Air-cooled diesel generators use air to keep the engine’s temperature at a minimal level. The air-cooled system allows the engine to take air from the atmosphere and circulate it internally across all parts of the generator.

On the other hand, liquid-cooled generators use oil or coolant to keep the engine’s temperature down. The pump circulates the cooling liquid to different parts of the engine to keep them cool during operation.

Air-cooled generators are not made to operate for longer periods because they can overheat, whereas liquid-cooled generators can be used for extended time periods. However, liquid-cooled systems are expensive than air-cooled units, but they are durable and powerful.

How long will a diesel generator last?

Diesel generators are tough and durable machines. The average lifetime of a diesel generator is somewhere between 12,000 and 20,000 running hours. After this time, your generator will need overhauling. You can increase the life of your generator by taking care of it. Changing oil, oil filter, and air filter on time, keeping the battery charged, and using fresh fuel help increase the generator’s lifespan. If your generator is not a closed frame model, we suggest using a generator cover or box to protect it from rainwater, dust, and harsh weather.

Which oil is best for diesel generators?

You will find tens of oils for diesel generators in the market. The best way to select oil for a diesel generator is to consult the user manual and then use manufacturer-recommended engine oil. Some companies also provide you with engine oil. A lot of generator experts suggest that you must choose the oil based on weather and running frequency. You can also consult customer services to get knowledge about oils.

How often should the oil be changed?

If you have an advanced model with an indicator for low oil/oil change, you don’t need to keep track of running hours for oil replacement. For basic models, you should check the oil condition periodically and replace the oil every 200-300 running hours.

Is a diesel generator more dangerous than gas/propane generators?

No. A diesel is generator is not more dangerous to use/operate than gas/propane generators. The safety measures are the same. You must read all the safety measures mentioned in the user guide before setting up your generator.

What are the drawbacks of a diesel generator?

A diesel generator has the following drawbacks.

Expensive: Compared to their gas and propane/natural gas generators, diesel generators are way costly. We agree that they are durable and reliable, but spending such a large sum of money is unaffordable for many people.

Less Variety: Diesel generators have a low range of models as compared to other single fuel generators.

Noise: The noise rating for diesel generators is higher as compared to gas and propane generators.

Portability: Diesel generators are heavier than other generators. Let alone the standby models; the portable models are also heavy to move around.

Cold Weather Problems: Most portable diesel generators are difficult to start in cold weather. Some models come with a choke or electric starting mechanism to overcome this drawback.

Final Words

Despite all the limitations/drawbacks of a diesel generator, it is still the most reliable and durable option for standby/portable power backup. They may be the least popular option, but the people who use them are delighted with their efficiency, durability, reliability, low maintenance, and overall performance. You can buy one from the list above according to your needs.

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