Diesel Generator Longevity Guide with Tips To Increase Life

A generator’s longevity is an essential consideration when looking at options for backup or standby power. It is no coincidence that people prefer diesel generators in many industrial, medical, and commercial settings. Homeowners are increasingly opting for diesel generators as a standby because they have many advantages over other kinds.

With proper maintenance, portable diesel generators can last 10,000 to 25,000 hours, while stationary diesel generators can last 12,000 to 50,000+ hours. Diesel generators are incredibly durable and can last more than thirty years with frequent inspections, maintenance, servicing, and cleaning.

Diesel generators come in a variety of sizes to suit different power requirements. To ensure maximum longevity, purchase one that can easily handle the anticipated load because overloading shortens its lifespan. Like any machine, you must regularly and adequately maintain diesel generators to ensure they last as long as they should.

The Life Expectancy of Diesel Generators

Diesel Generator TypeEstimated LifespanEstimated Running Hours
Standby20-25+ years12,000-50,000+ hours
Portable10-20+ years10,000-25,000 hours

Diesel generators generally have a longer life expectancy than generators that run on other types of fuel. They run at lower revs per minute than gasoline and natural gas generators and have comparatively simple mechanisms that make maintenance easier. For these reasons, there is less wear and tear on the engine components than with other generator types.

Most diesel-powered generators are water-cooled and run at 1800 RPM. Generators that run on other fuel types are usually air-cooled, and the engine runs at 3600 RPM. This means that many diesel-powered generators can go for a minimum of twelve thousand hours before requiring an engine overhaul. Some of them can go for much longer – more than twenty thousand hours.

If you use a diesel generator for four hours a day, it will take fourteen years to hit the twenty thousand hour mark. However, these figures are just averages because a generator’s lifespan depends on its manufacturing, how it operates, environmental conditions, and maintenance.

Standby Diesel Generator Lifespan

The size of the generator also affects its lifespan, with smaller generators having shorter life expectancy than large ones. The generator’s environment will also affect its longevity by freezing temperatures, high humidity, salty air, and high dust levels.

Generally speaking, diesel-powered standby generators can run for between twelve thousand and fifty thousand hours before engine overhauls are required. Runtime depends on the quality and size of the generator and how you maintain and use it. It is necessary to exercise a diesel engine periodically to keep it in good shape.

A user should inspect the generator regularly and thoughtfully when it is operating and standing idle to ensure maximum lifespan. Many people install a standby generator and then forget about it until something goes wrong when they need it. This is not the right approach. You should treat your generator the same way you treat your car by regularly inspecting, checking, and servicing it.

Diesel engines are valued for their durability, reliability, and performance under load. Standby diesel generators can take on a full-rated load in under ten seconds and go for more than thirty thousand hours between major overhauls. This equates to between twenty and twenty-five years of use on average.

A backup generator for your home can last as long as forty years with proper care and maintenance.

Portable Diesel Generator Lifespan

Portable generators are smaller than stationary generators and don’t last as long. Depending on engine quality, they can last between ten thousand and twenty-five thousand hours if adequately cared for. They are much cheaper than a standby whole house generator but also less reliable. Portable diesel generators tend to outlast those that use other fuel types.

Unlike a standby generator, you’re not supposed to run portable generators for days on end without a break. A portable generator with a life expectancy of twenty thousand hours can last for over twenty years with proper maintenance and servicing. Using good quality fuel and oil and protecting it from moisture and dust will help give it a longer life.

Portable diesel generators, though available,  are relatively rare and most portable generators run on propane or gasoline. Diesel engines are usually heavier and noisy, so they are not always a popular choice in the portable generator market. They are also more expensive than their gasoline or propane equivalents.

If you need to put your portable diesel generator in storage for some reason, drain all of the fuel from it and ensure the engine’s insides are lubricated. Keep it in a dust-free, dry place and charge the battery regularly.

Some brands of portable generators are better than others, so always try to source one from a reputable brand. Not all portable generators are equal in quality, reliability, and longevity. You should never operate any portable generator indoors because the fumes can be deadly. To protect it from the weather and extend its lifespan, build an enclosure for it outside where there is plenty of ventilation.

Diesel Generator Operation and Maintenance

Specific components will wear out and have to be replaced from time to time, but this is a normal part of a maintenance program. Regular maintenance includes removing water from the fuel tank and replacing the filters. Diesel generators run at half the RPMs of a similar-sized gasoline-powered generator and last twice or three times longer.

Whole house and other larger diesel generators have special programs that turn them on automatically and run them for a specified period. These are called generator exercisers, and users should ensure that they are working correctly at all times. Regularly exercising a diesel generator ensures that engine components are kept lubricated, uses up the fuel before it degrades, and prevents the oxidation of electrical contacts.

Your diesel generator’s lifespan depends on how you use it. If you work it very hard or let it sit idle for months between uses, this will shorten its life expectancy. Buying a generator with too much power output for your power needs is inadvisable because they need more preventative maintenance to avoid deposits building up inside the parts. Some manufacturers say that using the generator too little can be even worse than overusing it.

A generator should be exercised at least once a month for thirty minutes or more at one-third or more of the maximum load. Running it without a load should be avoided because fuel and carbon deposits build up and clog the insides. This is known as “wet stacking,” as unburned fuel goes into the exhaust system.

Diesel generators tend to have a sweet spot at between fifty and seventy percent of maximum power load. The sweet spot is the optimal fuel consumption-to-workload ratio. Higher workloads burn fuel more efficiently, making running the generator on a heavier load than a lighter one can be cheaper. For long-term prime operation, an eighty percent load is the recommended maximum for a diesel generator.

Wet Stacking In Diesel Generators

Wet stacking is undesirable in diesel generators. A sign of wet stacking is when a dark, thick liquid resembling engine oil drips from the generator’s exhaust. It occurs when you operate the generator at a light load for long periods.

The diesel fuel burns off properly, and the soot and residual fuel end up in the exhaust system. When the load is consistently too light, the engine does not reach its optimum operating temperature. The engine runs hotter with heavier loads and therefore burns up all the fuel.

Wet stacking can occur when the generator is unused for long periods, has too little fuel, or has too much fuel. It can also happen if the load is less than 60% of the maximum or runs colder than its recommended operating temperature. Wet stacking may cause the engine to stutter or miss during operation.

The mixture of fuel and carbon deposits can build up around fuel injectors, causing them to deliver more fuel to the engine cylinders than they should. This causes more unburned fuel to build up in the exhaust system, and so it becomes a vicious cycle of wet stacking. It can eventually result in reduced performance and even permanent engine damage.

If the engine operates below its optimum temperature, the piston rings do not seal the gaps between the pistons and cylinder walls, leaving space for unburned fuel to leak into the oil pan. This causes the engine to wear. Exercising the generator for around 30 minutes a week on a heavy load prevents wet stacking.

Ensuring the generator is routinely serviced at least once a year is another way to prevent wet-stacking.

What Should Diesel Generator Users Do To Ensure Longevity?

If a generator sits for too long without running, the lubrication drains away or dries out, and the moving parts are more likely to experience increased friction when they startup. This increased friction adds to the wear and tear on engine components. Since diesel generators startup so fast, they can quickly go from very cold to very hot. Such rapid temperature changes are not good for the generator.

If you don’t use the generator often, you are also less likely to see problems that you need to address when they occur. When you use it regularly, you will quickly notice which operating patterns are standard and which ones aren’t. For instance, is it smoking more than usual, does the engine sound different, is the exhaust much louder, or is there increased vibration or oil consumption?

Suppliers of whole house generators usually offer a service that schedules regular preventive maintenance based on environmental conditions, and the generator’s load regularly runs. A generator that frequently operates in extreme weather conditions will need a more rigorous maintenance regime than one that runs only periodically and in relatively mild conditions.

With smaller portable diesel generators, engine repairs, unplanned maintenance, and you should have qualified professionals perform overhauls. Users can conduct basic inspections that include checking oil, fuel, coolant levels, and battery terminals’ connections. When it comes to more technical interventions, it’s best to call in the experts.

Preventive maintenance is critical to maximizing a generator’s lifespan. The frequency of services will depend on usage, environmental conditions, and running time. As a general rule, you should service the generator once every six months. If you live on the coast, ensure that the generator enclosure does not allow sand and saltwater to contact the machine. These are contaminants that will shorten the generator’s lifespan by causing damage to its components.

You should locate a standby generator in a protected but not enclosed area where you can ensure weathering to the generator is minimal. These days many of them come with cabinets or enclosures that help reduce noise levels. Its location should be easily accessible for inspections, maintenance refueling, and servicing.

Remove insects, ant nests, and rodents from the generator’s enclosure as soon as you see signs of their presence. Don’t allow dead leaves and other garden debris to accumulate around the generator, and try to keep it free of snow.

It is best if oil changes occur after every one hundred hours of use, but when in doubt, check the operator or service manual supplied by the manufacturer of your particular unit.

Spark plugs will also need changing periodically, depending on how long the generator has been running. Some say you should switch spark plugs out after every two hundred hours of operation, while others say you should replace them annually.

Diesel Generator Preventive Maintenance

Mechanical problems can create hazardous conditions when the generator is running, and preventive maintenance is vital to ensure a generator’s longevity. If you address a problem as soon as you become aware of it, you reduce the risk of it compounding over time and causing even more damage.

Preventive maintenance of a diesel generator includes –

  • general inspection,
  • checking the cooling system,
  • ensuring the engine is well lubricated,  
  • checking the alternator for dirt
  • ensuring fuel lines are securely attached and undamaged and
  • testing and servicing the starter battery.

A general inspection should cover the electrical system, the exhaust, the fuel feeds, the alternator, and the engine. The exhaust system consists of the exhaust pipe, muffler, and exhaust manifold. All joints, gaskets, and welds in these areas must be regularly checked for leaks and repaired immediately.

Also, ensure that the exhaust pipe is not causing surrounding parts to overheat. You should inspect the exhaust system with the generator running to identify any leakages or overheating. Generators with control panels will sometimes have diagnostic programs that alert you to potential problems or specific areas that you should check.

Inspect the fuel filters, fuel supply lines, and fittings for any cracks, damage, or blockages in the fuel system. The fuel lines should not be rubbing against any other parts because this could eventually cause them to split or break. It is best to do this while the generator is operating.

Inspect the battery terminals if the generator has an electrical starting system (they usually all do except the smallest portable generators). The connections should be clean and tight. If they are corroded or loose, the generator may not start when you need it.

As far as the engine is concerned, you should regularly check the fuel, coolant, and oil levels. If there is a potential problem with the engine, you can usually hear it when the generator is running because the regular sound changes. The engine may be misfiring or using more fuel or oil than usual. Excessive vibration and more exhaust smoke are also signs that there could be an engine problem.

A diesel generator needs proper lubrication at all times to avoid excessive wear and tear. This means that regular oil changes and replacing the oil filter are necessary. You should check the oil level while the generator is off. The manufacturer will usually provide instructions on how to change the oil filter and drain the oil. Always use the oil type recommended by the manufacturer of your specific generator.

Larger diesel generators use a coolant mixture of antifreeze, water, and coolant additives. You should check the manufacturer’s recommendations to see which type of coolant to use. If your generator has a radiator, inspect it for dirt and foreign substances and remove them with a cloth or soft brush. Be gentle so you don’t damage the radiator fins.

You can use compressed air or a jet of water to blow unwanted material out of the radiator. After the engine has cooled, you should remove the radiator cap to check the coolant level. Generally speaking, it should be three-quarters of an inch below the radiator cap, so you may need to top it up.

Water vapor accumulates in the fuel tank and then condenses, which means water builds up inside the tank over time, along with other sediments. It is therefore essential to drain the fuel tank periodically and check the fuel filters. Ideally, you should use diesel within a year of purchase, so exercising the generator set helps use up the fuel before it deteriorates.

It is also necessary to check the engine air intake and replace used filters. The conditions that you operate your generator in will dictate the required frequency of these checks. Dusty conditions will necessitate more frequent cleaning of air intakes and air filter replacement. Sometimes an air filter can just be cleaned off and reused if undamaged.

Batteries deteriorate over time and can lose their charging capacity. You should replace them when they can no longer hold a charge because they will no longer start the generator. Regular inspection and testing of the generator under load can reveal potential battery problems. Some generators have built-in programs that test the batteries when the generator starts, but it will be necessary to use a manual battery load tester for others.

If there is a build-up of dirt on the batteries, you should wipe them down with a damp cloth. Corrosion on the battery terminals can be dissolved by removing them and cleaning them in a solution of a quarter-pound of baking soda to one quart of water. Rinse them in clean water, dry them off and then re-attach them to the battery. The experts recommend that you coat them lightly with petroleum jelly to prevent further corrosion.

You should check the battery cells every two hundred hours, and if the electrolyte level is low, top it up with distilled water.

Diesel Generator Maintenance Checklist

It is helpful to keep a maintenance checklist that records when you last changed the oil and swapped out the spark plugs, etc. You can break a maintenance checklist down into weekly, monthly and annual procedures. Your standby generator will usually require maintenance by the supplier or technicians trained on that specific brand of generator.

If your generator comes with a maintenance or service plan, you should always check with the supplier what you should be doing to maintain the generator. Your primary responsibility may be to make sure that services take place regularly and inspect the generator visually. Every time the generator starts up, you should pay attention to how it sounds, and of course, you should ensure that the exerciser is always on.

The checklist below gives you an idea of the things that you should do for preventive maintenance. Some of these procedures should only be done by experts.

Weekly Procedures

  • Visual inspection for loose connections, damage, leaks, wear, and corrosion
  • Check oil levels – top up if too low
  • Check coolant levels – top up if necessary
  • Clear air inlets and outlets of all debris
  • Verify battery voltage and operation
  • Clear enclosure of dead leaves, insects, ants nests, and rodents – call pest removal if necessary as rodents can do a lot of damage to wiring and clog the exhaust and air inlets
  • Run the generator for ten minutes or until it heats up to its optimum operating temperature
  • Ensure that it is in auto mode for automatic startup
  • Make sure the circuit breaker is closed
  • Check for fluid leaks

Monthly Procedures

  • Automatically start and run the generator for at least 30 minutes on 60% load or higher.
  • Examine the engine for leaks, abnormal engine noise, or smoke emissions
  • Check the wiring to make sure electrical connections are tight and that there is no corrosion
  • Check the engine coolant thermal protection level
  • Check the battery electrolyte level and top it up with distilled water if necessary
  • Inspect the battery posts, cables, and charger for proper operation, connections, and battery load
  • Check engine drive belts and fan belts for tension, wear, damage, and cracking
  • Examine fuel lines and fuel hoses, and connectors for breaks and leaks
  • Inspect the exhaust pipe, muffler, and exhaust manifold
  • Check the control panel for any alerts

Annual Procedures

  • Change and replace engine oil and oil filters
  • Change the air filter
  • Change and replace drive belts and fan belts where worn or damaged
  • Flush the cooling system and check the coolant concentration
  • Replace spark plugs
  • Replace engine air filters
  • Clean the crankcase breather
  • Exercise the generator for at least one hour at maximum load.
  • Remove water from the fuel tank
  • Fuel testing and reconditioning


Diesel generators have some of the longest lifespans of all generator types, but they must be appropriately and regularly maintained. Don’t overload them, don’t run light loads all the time, prevent wet stacking, exercise them frequently, and they will reward your investment for decades to come.


Hubert Miles

I've been conducting home inspections since 2002. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and an FHA 203k Consultant. I started PickGenerators.com to help people better understand whole-house and portable generators.

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