This Is How To Drain Oil From a Generator

When your generator has been running and providing power to your home for a long time, during emergencies, or to help your power bill go down, you need to maintain it. Changing the oil for your generator can either be extremely easy or be one of the more complicated things you can do.

To drain the oil from a generator, place the generator on raised blocks and start the engine to heat the oil. Once the engine is warm, remove both the oil cap and dipstick. Place a catch pan under the generator, and allow the oil to drain out of the system until the generator’s oil tank is empty.

In theory, it sounds straightforward to have your generator drained from its oil; however, each type of generator has its way of being drained. Further, we recommend knowing all the reasons you should drain the oil, how to do it perfectly, and which oils are the most commonly used.

How Do You Drain Oil From a Generator?

These are the steps you will follow to remove the oil from your generator; they are generally the same for all machines and can transfer them. We have listed each step all on their own, allowing you to easily follow along with each one when you have to start removing the oil.

Removing the oil in your generator is only something that should sound daunting if you have not done it in several years. However, if you do it regularly, not only will the oil draining process be quick and painless, but your generator will also last longer than even you will.

Warm Up the Engine

We will need to heat the oil stuck throughout your generator before we do anything with the generator, including moving it. Cold or even room temperature oil will not simply flow out of the generator, leaving a lot of the oil behind in the engine and the oil pan.

The engine needs to be at operating temperature but not so hot that you start sweating just when you are near it. Usually, a generator will reach this temperature after 10 to 15 minutes of running, even if not put under load. However, it’s best to put a light load on it.

Lifting the Generator

You will find many people choosing not to do this; however, it is a lot easier moving an empty oil catcher than one filled with old oil. Lift the generator onto wooden blocks, a workspace that gives easy access, or even lifts it with a car jack and put it on jack stands.

Not only will this make the entire process easier, but it will also save you the headache of trying to move an oil catch pan filled to the brim. Many people underestimate just how much your generator, even a small one, can hold when filled.

Get Oil Trap Ready

Now that the generator is both warmed up and lifted into the right position, we need to get the oil trap ready, whether using the nearest bucket or a dedicated oil pan. You must place the bucket under that generator with the bolt on the oil pan straight above the oil trap.

Your oil trap should preferably be large and flat and able to hold anything from 10 to 30 liters of oil, with larger generators usually filling much larger oil traps. The most common thing we’ve seen people use oil traps that are too small only to have to change it out as it starts overflowing rapidly.

Undo Bolt and Remove Oil Dipstick

As soon as you remove the bolt from the oil pan, it will start draining hot oil, which means you need to be ready. Remove the oil dipstick first; if your generator has one, then use a ratchet or spanner set to remove the bolt located at the bottom of the oil pan of your generator.

You will notice that as you turn the bolt, it will become easier to remove the spanner or socket and turn it with your hand. Be ready to twist it fast and remove it and your hand as fast as possible, as the oil will be hot and can burn your hand if you are not fast enough.

Wait For Oil to Drain Out

You may be surprised, but even if the oil is perfectly hot, but the oil can take a while to drain out of your generator completely. It should take between five to twenty minutes for all the oil to drain out of your generator; you will not have to shake or apply any pressure to push out all the oil.

Many people take this moment to check the quality of their oil, checking if there are any flakes of metal in the oil. You should consider sending the generator in for a complete repair and check if you see any impurities or debris in the oil.

Reinstall Oil Plug

Once the oil is no longer flowing out from the generator, you can close the plug; many people prefer to put a drop of blue Loctite on the plug. This will not make it impossible to remove the plug later, but it will prevent it from being shaken loose as the machine is running.

However, please use a torque wrench when reinstalling the oil plug; every oil plug needs to be tightened only to a specific level. If you overtighten the plug, you will have no oil leak in the immediate problem, but you will strip the bolt, causing hours of headaches when it becomes completely stuck.

Replace Oil Filter

Once you install the bolt, we need to start replacing other parts of the oil system for your generator, mainly the oil filter. You should do this while the engine has no oil in it, or else you will be overwhelmed with the oil suddenly flowing out of the generator.

Most smaller generators will not have large oil filters, but you should still replace the small ones found on them. Ensure to lubricate the seals on the oil filter before tightening it; never tighten your oil filter any more than hand tightening, as the threads on the filter can easily strip.

Refill Oil Through Oil Dipstick Hole

Once everything has been closed, you will need to refill the oil in the generator; unlike engines that have dedicated oil fill holes, generators use the dipstick hole. You should preferably use a funnel to ensure that you are not spilling oil all over the generator, engine, and floor.

Fill the oil tank until you see the oil coming up to the threads of the hole or until it reaches the maximum level indicated on the dipstick. We recommend running the generator a bit once it has reached this level and to measure again. Adding a bit more oil when you notice it dropping too far; be sure the generator is not running when adding more oil to the system.

Where Is The Oil Drain Plug On a Generator?

The drain plug on a generator is usually on the bottom of the unit, underneath the engine. The plug is typically metal, steel, or aluminum to prevent it from deforming from the generator’s heat.

The oil plug will always be at the lowest point of your generator engine to ensure that the oil can be drained and allow the pistons to dip in it. This location also serves to help the oil keep any metal flakes or broken parts away from the rest of the engine while it is working.

Oil cannot suspend contaminants properly if there is nowhere it can safely place all the oil that contains the contaminants. There are many more reasons why the oil pan and the oil drain plug are at the uttermost bottom part of the generator, but they are not crucial for draining it.

Why Should You Drain The Oil From a Generator?

Now that you know exactly how to replace your generator oil, it is also vital to understand why you should be replacing the oil in your generator. There are several reasons that your generator needs to have the old oil removed and why you need to replace the oil with something new and clean.

We have several reasons you need to change your oil regularly, ranging from age to how often you use the generator. You need to be aware of these issues as you can be ignorant of many of them, causing long-term damage to your generator that can cause a lot of damage to your system.

  • Old Oil: The easiest reason to understand why you should be changing the oil in your generator is that it is simply too old. Oil does not last forever, and the heat produced from a generator causing the oil to degrade slightly faster than normal.
  • Broken Parts: If something in your generator has broken, aged, or being worn out, the oil will naturally start to catch all of this. You will need to replace the oil completely once you have fixed everything inside the generator; the oil that held onto all the junk needs to be replaced.
  • Maintenance: Just general maintenance of running your generator throughout the year or when the machine has been running for more than 100 hours. The oil will be one of the most important things to your regular maintenance, keeping everything running smoothly.
  • New Oil: Older generators or systems that have been in storage will usually benefit from newer oil technology. As the chemicals are increasing and improving the way that the oil can work with the machine, helping to clean it and keep everything running smoothly.
  • Wrong Oil: It may seem odd, but the wrong oil can be in your generator, and you will have to remove as much of it as possible before extensively running your machine. Oil created for diesel generators is entirely different than oil made for petrol generators.
  • Coolant Leaks: If your generator is leaking any fluid into the oil, then it will be extremely detrimental to the quality of the oil in your generator. You will need to ensure that the generator is not leaking unwanted fluids like coolant or gas into the oil.

What Are the Types of Oil You Should Get for Your Generator?

When you are busy getting everything ready to have your generator oil changed, you will eventually find the problem of choosing the best oil for your machine. Simply putting into the search of any website or google will, however, flood you with every type of oil ever made.

We have sifted through several of the available oils for your generator, choosing five that are the best for every type of generator. Each one will help you have the best possible lubrication inside your machine.

Castrol EDGE

The standard oil that you will find at every auto parts store and website that you can imagine. It is a fully synthetic oil with several iterations aimed at either petrol engines, diesel engines, or older engines running on lead replacement fuel.

In your generator, it will last the standard 100 hours and may even be able to handle a bit more if you are lagging in doing your generator services. We will mention that EDGE is better to use than the Mobil-1 variant from Castrol as it can handle much higher temperatures.

Honda SAE

If you have a Honda-powered generator, the simple truth is that you can settle for the regular Honda SAE oil that the company provides. The Honda SAE line of oils can help their diesel and petrol engines run smoothly and handle the much higher temperatures these engines run at.

However, it’s important to note that the oil only comes in 32-ounce bottles, which means you need to buy several bottles when you need to do maintenance. We recommend that you have only use the Honda SAE if you have a portable generator as it will use less oil overall.

Briggs & Stratton Oil

Another manufacturer of petrol and diesel engines, Briggs & Stratton, is easily one of the more reliable engine manufacturers. With a part of the company focusing on making engines for generators, they have also made servicing their engines much easier.

Coming in several sizes, we recommend getting the 48-ounce bottle to have your generator serviced at home properly. Further, using the engine manufacturer’s oil means that you can safely have the oil running in your generator without having to stress about whether or not the oil will be right.

Shell Rotella Oil

Mainly aimed at diesel engines, the Shell Rotella oil from one of the largest fuel producers in the world is perfect if you need something that will always be the same. Available in 5-gallon buckets or just 1-gallon buckets, the oil is refined to help you safely keep your generator perfectly maintained.

Remember that the Rotella oil line from Shell is for diesel engines, and you cannot use it with your typical standby generator. However, if you have a larger diesel engine generator, you can comfortably use it to keep your machine running perfectly.

Pennzoil Ultra Platinum

Oddly enough, we have seen many people prefer to use Pennzoil when they are not sure about which oils will work with their generators. This is because the oil is better known in the United States than some competing oils that will work the same or better than Pennzoil.

However, like some other oils, this is not available in larger packs as you’re supposed to use it only for smaller engine systems. We recommend only using it for your smaller, portable generator as it will easily have your generator lubricated and running when you need it in the middle of nowhere.

How Much Oil Does a Generator Take?

Generally, a generator will need around 1.1 to 1.9 quarts filled with oil if it is a portable or normal standby generator. However, if you have a larger standby generator, it can easily use over 5-quarts of oil to fill the engine and oil pan.

As your generator grows in size, the amount of oil that it needs will drastically increase; however, the more oil a generator hold, the longer the oil can last as well. Further, if your generator is small, then you can expect the oil to need replacing a lot faster.

We have seen several people who assume their portable handheld generator that can fit the passenger seat needs new oil rarely. However, these generators are usually much easier to fix and give new oil to as they only require a few quarts of oil every few hundred hours.

What Happens When a Generator Runs Out of Oil?

Despite everything that people may assume when your generator runs out of oil or uses old oil, it will not simply survive a bit longer. However, it will greatly damage the generator and greatly impact the overall functionality of your generator, with most completely failing if left for too long.

Your generator needs lubrication to work properly, getting the generator to run as smoothly as possible without almost literally destroying itself. Generally, four things will happen as your generator starts to run without any oil to suspend problematic substances.


There is nothing to prevent the parts from rubbing against each other, causing the machine will overheat, regardless of its coolant levels. When you run your generator with not enough oil or with no oil at all, the pistons inside the generator’s engine cause them to start melting due to friction.

Often people assume that the only thing that oil does is prevent damaged parts from creating problems. However, this is not true; instead, the oil helps to suspend everything inside the engine, ensuring that the only heat generated is the heat from the internal combustion.


The extension of not being able to cool everything, the pistons will start rubbing against the sides of the engine block. As the engine moves, it becomes hotter and hotter as the suspended components heat themselves until the engine parts literally melt together into one solid piece.

You need to ensure that the generator has enough oil and that it is of high enough quality to properly work for the hours upon hours you may need it to. Several people become confused when their generator suddenly refuses to even turn after running without oil for hours.


This can happen slowly, usually deforming some of the sensitive parts within the generator first, like the oil rings or the seals around the engine. When this happens, it is an immediate sign that you need to immediately replace the oil, install a new filter, and have everything working as properly as possible.

If running for too long, the pistons will start to melt inside the generator, usually becoming warped and inefficient if caught in time. However, it’s important to note that all heating problems caused by insufficient oil in the generator will cause damage.

Complete Failure

If the generator is run for too long or repeatedly started without any oil, the entire system will fail. Unlike other failures that you can quickly repair, there is no actual way to fix an engine that has seized owing to having old oil or not having any oil at all.

You will need to replace almost your entire engine, have the engine blocked bored out to fix the warping, fix cracks in the engine block, and replace all the parts attached to the pistons. You need to ensure that your generator is always running with fresh and enough oil to save thousands.


Your generator needs to have fresh oil installed at least every 100 hours, and you can do the entire process in your backyard. The process is only daunting when you try and do it the first time; fortunately, short of reading no instructions, it is rather difficult to do wrong.

Always remember, a few minutes of reading instructions saves months of headaches of trying to fix it!


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 to help people better understand whole-house and portable generators.

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