Proper Engine Winterization Ensures Reliability Come Spring

By Brad Murphy

Spark Plug

Many of us have already started to prepare for winter. We bundle up with heavier gear to ensure our bodies stay protected and warm against winter’s chill. But we aren’t the only ones that need protection against nature’s harsher elements.

For many contractors, equipment is used very little during the winter season — and in some areas of the country, not at all. If a piece of equipment will sit idle 30 days or more, it’s necessary to winterize the engine.

This is the time of year when equipment owners begin to ask themselves, “How do I prepare my engine for the winter?” But first, it’s important to understand why you should winterize. Winter brings freezing and — even worse — below-freezing temperatures. In order to avoid damage to the engine and other important components of the machine, it’s essential to winterize. Four primary areas must be addressed to ensure reliable operation come spring.

1. Clean and inspect

The first step in preparing an engine for winter storage is to give both the engine and the machine it is powering a good cleaning. Shut down the engine and allow ample cooling time, then simply wipe the entire unit clean with a towel. Leaves, grass or other debris should also be removed at this time. An air compressor may be used to dislodge any particles that can’t be reached by hand.

Checking the condition of the air filter is another important practice that can prevent significant damage. A clogged, wet or damaged air filter can lead to a loss in power, or it might cause an engine to not run altogether — resulting in downtime from idle equipment and wasted time troubleshooting. Worse yet, a neglected filter may shorten the life of an engine by allowing dirt or water into sensitive areas. Therefore, the air filter should be cleaned or changed, if necessary, before putting equipment away for the winter.

A paper air filter should always be changed prior to winterization. However, if a foam filter is relatively new it can be cleaned and reused. Use hot soapy water, and let the filter drip dry before putting about one ounce of oil on it. Squeeze the filter to saturate, and then blot with a paper towel before reinstalling.

2. Fuel considerations

Now that the engine has been thoroughly inspected and cleaned, it’s time to consider the fuel. One of the primary reasons engines must be winterized if idle for more than 30 days is because that’s the point when fuel begins to go stale. Stale fuel leads to residue build-up, which can plug the small fuel jets in the carburetor and cause major headaches — and costly repairs. There are two primary methods to address this problem.

The best approach is to drain all the fuel out of the gas tank, then start the engine and run it for a few minutes to ensure the fuel lines and carburetor are free. This option eliminates any potential issues with stale fuel down the road.

Another acceptable approach is to completely fill the tank and then add fuel stabilizer. Especially in extremely cold climates, a half-full tank leaves room for condensation build-up. This can quickly cause rust to form inside the tank, so it’s important to ensure the tank is completely full. However, it’s only wise to go this route if the engine has a fuel shut-off valve. Upon filling the tank, shut off the valve and run the engine until it dies. Doing so ensures the carburetor is dry and leaves no chance for moisture accumulation.

3. Oil adjustment

It’s common knowledge that oil is essential to engine operation for many reasons. In day-to-day operations, changing the oil is considered a routine part of a maintenance program; in winterization, attention to oil is just as crucial.

Oil becomes contaminated from normal engine combustion during operation. Acid builds and, if left to sit during winter, might cause corrosion. The same is true of water and other particles that can contaminate oil during typical operation. Also, oil that sits for too long can become thick and gummy, preventing a smooth start come spring. Be sure the engine has fresh oil before storing the equipment.

Because colder temperatures might still be present when it’s time to start up the equipment in the spring, it’s also a good idea to adjust viscosity at this time. Multi-viscosity oil is a great option — especially in areas with unpredictable or harsh temperatures because it recognizes outdoor temperature and adjusts to proper viscosity.

4. Spark plug check

Finally, it’s important to replace spark plugs prior to winterization, as dirty or damaged plugs can cause a decrease in power and lead to poor starting performance come spring.

Remove the existing spark plugs, and then put a teaspoon of oil into the plug. Pull the recoil over a few times until resistance reaches its maximum. It’s at this point, top dead center, that both the intake and exhaust valves close, leaving no room for moisture, debris — or even a pest — to get inside. This process also provides the dual benefit of distributing the oil across the head, rings and valves, while preventing moisture and rust in the combustion chamber.

Upon replacing with a new spark plug, set the gap as instructed in the owner’s manual, and replace.

Spring troubleshooting

Spending just a few minutes to winterize an engine can ultimately save operators a lot of time and frustration in the future. But even the best-laid plans can go awry. So if the engine wasn’t properly winterized, wasn’t winterized at all, or if something simply went wrong, here are a few strategies to help troubleshoot if engine issues show up come spring.

After taking an engine out of winter storage, the most obvious problem is that it won’t start. And even if it does start, the operator may notice a reduction in power. If either of these are the case, the first step is to do all of the traditional pre-winter maintenance tasks again. This includes cleaning the machine, checking and possibly replacing the air filter, and checking the spark plug. In addition, the oil should be changed and fuel replaced.

That being said, it’s understandable that most people don’t have the time or simply don’t want to spend the time re-doing all of the maintenance steps. So for those looking to save some time, focus on the three major things that an engine needs to run: gas, spark and good airflow.

The first area to check is the fuel and its filter. Stale fuel makes starting the engine difficult, if not impossible, once the machine is taken out of storage. To get the engine up and running again, first drain out the existing fuel. The filter should then be removed and shaken out over a clean cloth to displace any remaining fuel, then a cloth can be used to wipe away any residue from the outside of the filter.

If that doesn’t solve the problem, the next area to check for quick troubleshooting is the spark plug. The oil that was added to the cylinder before the machine was stored may have fouled it. Clean or replace the spark plug before attempting to start the engine again.

The final area to check is the engine’s air filter. An air filter is a very inexpensive component that has to do a tremendous amount of work. And when it works, all is well. But, when it doesn’t, it can lead to costly problems, as equipment needs clean air to efficiently burn fuel. If the engine isn’t running at the optimum level or still doesn’t start, check the air filter and clean or replace as necessary.

If the engine still refuses to start, the carburetor likely needs cleaning. It might seem a bit intimidating to clean a carburetor, but it’s a fairly simple process. However, it’s also perfectly acceptable to take it to a professional for cleaning.

To clean the carburetor, remove the bowl and locate the main jet, usually on the bottom of the bowl. When the main jet is located, spray a fine wire with carburetor cleaner and use to clean out any gunk or debris. If this at-home cleaning process doesn’t work, the carburetor should be taken in for further analysis and adequate service.

Another problem that could occur once an engine comes out of winter storage is recoil issues or hard engine starts. Both can also be attributed to corrosion issues. If the pre-winter spark plug process was neglected or done incorrectly, the oil may not have been distributed, potentially causing corrosion and rust to form, and making it difficult, if not impossible, to pull the recoil. Be sure that the recoil is properly lubricated.

If it ends up the recoil is in fact properly lubricated but hard starts continue, it’s best to take the engine in for service. Fixing the recoil is a specialized, and potentially dangerous, process that is best left to professionals.

Understanding the primary areas to address before storing an engine for winter will further helps to identify and fix any problems that crop up come spring. Although it might appear time consuming to prepare an engine for storage, most steps are fairly quick and easy to perform. And a few minutes spent on proper maintenance before winter is a small investment to make for big returns come spring.

Brad Murphy is executive vice-president and COO for Subaru Industrial Power Products, and an expert on proper maintenance and winterization of small, air-cooled engines. For more information, contact Murphy at

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