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23Jan 2023

Diesel generator: What's the difference between air and liquid cooling systems?

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Generator cooling system comparison.jpg

Why do diesel generators need cooling?

It is well known that there are many metal components on diesel generators, all of which generate heat as current flows through them during generator operation. Heat can build up quickly within the diesel generator, creating additional heat that must be properly removed to reduce the risk of damage. If the heat is not properly removed from the generator system, the windings can quickly fail. Then there will be many problems affecting the normal operation. However, diesel generator cooling system can significantly reduce this heat that keep the generator cool and minimize the risk of damage to the generator itself.

Most diesel generators are air-cooled or liquid-cooled cooling method, and the cooling method is one of the basic design elements of generator manufacturing, is usually determined by the size and type of the generator. Air cooling systems are typically used on smaller diesel generators, while larger diesel generators require liquid cooling. For this reason, industrial large generator manufacturers are more liquid-cooled. Now, in this article, BISON diesel generator manufacturers take you to learn more about difference between air-cooled and liquid-cooled generators.

Air cooling system

This cooling system uses air circulation to reduce the temperature. In an air-cooled system, the BISON engine takes cool air from the atmosphere and blows it through the different parts of the generator set. This prevents the generator from overheating.

Air-cooled systems are commonly used for portable generator sets and backup generators up to 22 kW. Air cooling system can be used for open frame or enclosed diesel generator sets. In an open ventilation system, the atmosphere is used with a type of exhaust system. This allows the air to be released back into the atmosphere immediately. It sucks in air and pushes it back into the surrounding area. In a closed system, air can be kept in place. What it does is recirculate the air. At the same time, the air is cooled, thus keeping the BISON generator cool.

However, the air-cooled system may still overheat the generator when it is used for a long time, which means that the machine needs to stop working, that is, stop power supply, and wait for the temperature of the generator to drop.

Liquid cooling system

Sometimes called a water cooling system, is another option. In a liquid-cooled system, the generator uses oil or coolant to cool the internal parts. Liquid cooling uses radiators and water pumps. This pump uses hoses to distribute coolant to the engine block. Heat from the engine block is transferred to the coolant, which flows into the radiator where it is cooled. Generators above 22 kilowatts mostly use liquid cooling systems.

Liquid-cooled systems are more expensive to produce, but they are more durable and powerful than air-cooled systems and are the most common choice for commercial and industrial use.

The difference bewteen air cooling and liquid cooling diesel generator


Air-cooled diesel generator features an engine that uses a fan to force air through the engine to cool the engine. Therefore, generators with air-cooled engines can often be used for short-term power supply applications, they can still power your entire home during a power outage, so they're an ideal backup system.

On the other hand, a water-cooled engine contains a closed radiator system for cooling. This engine cooling system is similar to the systems in many automobiles. Liquid-cooled engines tend to be used in higher kilowatt generators as larger engines require higher power output levels and reduce the amount of heat generated by larger engines. As expected, the larger the engine, the longer it takes to cool down.

Larger homes can take advantage of the added horsepower of these liquid-cooled engines. Other common users of these engines include convenience stores, restaurants, offices, and many more industrial, large buildings, and applications. Always consider what application you intend to use the generator for, as this can change the amount you may end up spending.

Generator size

Compared with liquid-cooled generators, BISON air-cooled generators are smaller in size. It is easy to install and can be placed directly on soil or concrete blocks. Liquid generators weigh four times as much as air-cooled systems. Due to their large size, powered equipment is required to move them from one place to another. The system is placed on a prepared bed or pedestal.

Cost comparison

Speaking of cost, the price comes down to size and power. Liquid cooling systems are more complex and designed with more components. They are precision engineered to operate efficiently with heatsinks (and other components). They are overall stronger, more durable, but diesel water-cooled generators are also more expensive.

Although air-cooled systems are less efficient for larger generators. However, they are small and easily mobile, so they are often an affordable option for everyday users for importers looking for a simple system for a small generator.


Liquid-cooled generators are usually bulky and consist of complex mechanisms capable of generating large amounts of power, with cooling mechanisms that allow them to efficient function even in extremely hot weather. The air-cooled generator is not the same, the volume is lighter, the structure is simple, and the efficiency is low.


Air-cooled generators are often easier when maintenance is considered. Without the complicated work of a liquid-cooled engine, and without the mess of a cooling process, an air-cooled process is easy to maintain. Keep in mind that air cooled generators involve maintenance but are simpler and less time consuming than liquid cooled generators, for a business or shop all it requires is checking the oil level from time to time and making sure the alternator's batteries are There is voltage and everything is fine. It's simple and saves time, which is what every workplace wants because time is money.

However, the cooling process for a liquid-cooled engine on a generator is a little more complicated and therefore requires some monitoring by the generator owner. In addition to checking the antifreeze level, you must also ensure that the coolant is functioning properly, which may mean checking lines and connections, as well as checking for potential leaks. Liquid-cooled engines also require more frequent maintenance, as it's important to catch any potential problems promptly. This may be a disadvantage to some, but the extra maintenance is worth it for the efficiency and power of the liquid-cooled engine. Maintenance kits for these generator types are readily available and should be used on a regular basis.

Noise level

Another key consideration is noise levels. Depending on usage, air-cooled engines do produce a fair amount of noise, as the fan can be heard blowing air across the engine. Also, engine noise cannot be further reduced with an attenuating enclosure due to the airflow required to keep the engine cool. This can be annoying, especially when the air-cooled engine is powering the house 24/7. If the generator is being used as a backup, it shouldn't be a big deal. However, this is something suppliers need to be aware of, as noise is something that many people dislike about generators. Another consideration is how your local homeowners association or community might feel about noise levels.

On the other hand, liquid-cooled engines are very quiet compared to air-cooled generators because the sound they produce can be contained within an attenuated enclosure. This is often a very attractive factor for many, but price and overall needs should come before comfort and preference.

Air Cooling vs Liquid Cooling Diesel Generator

The air is cooled by the engine, simple system

Closed radiator system, more complicated

CostMore expensiveMore economically
EfficientHigh efficiency and more powerLess power
Noise LevelVery QuitLarge Noises

Short term household power supply

Long term industrial, large buildings and applications

Which system do you need?

Each system has advantages and disadvantages. Air-cooled systems are simpler, cheaper and less prone to maintenance issues than liquid-cooled systems. Liquid cooling systems are more powerful and efficient, but also more expensive. At the end of the day, you need to choose the right generator for your business that is good enough for your needs. Air-cooled systems are very capable in the range they are used. Most home generators will not have air cooling issues unless the ambient temperature is very high.

BISON manufacturers hopes this information will help you learn more about air and liquid cooled generators and help you get the best deal for your needs.

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