How Long Can An Engine Sit Without Being Started?

Good aircraft management can be relatively straightforward if you regularly fly. By keeping the oil temperature up and preventing a buildup of moisture, the plane can be ready and willing to be flown at short notice. 

However, if you do leave an engine to sit without starting it can prove problematic. This only gets worse the longer you leave it so it is a good idea to know how long you can leave it without being started and what you should do to get it back in ideal flying condition. 

How Long Can An Engine Sit Without Being Started?

In this guide, we will look at why you should not leave an engine sitting, why a plane cannot be left idle for too long, and the best way to fly a plane if it has been sitting idle. 

Why You Should Not Leave An Engine Sitting

Poor management of your engine can lead to increased maintenance and even malfunction so you should look after it properly. There may be some guidance from the plane’s manufacturer on how long you can leave the engine sitting. 

So how long can you leave an engine sitting? Well, some planes suggest as long as 60 days as a maximum with simply preservative oil.

There is also research from oil analysis that suggests a piston engine can be considered inactive with less than five hours of flying time every month. 

The period of time you can leave an engine sitting can depend on the conditions where the plane is kept. If the hangar can keep a level temperature, you should be confident that you can leave it for over a week.

However, a lot of the issues for a sitting engine are to do with moisture as this will need to be burned off during a flight and for the oil temperature to rise sufficiently for stable and efficient flying. 

Why You Should Not Leave A Plane Idle For Too Long

Not only should you not leave a plane idle for too long for the engine’s sake but also for other parts of the plane. Every time an aircraft is parked, a checklist is followed as storage can become complicated and constant maintenance is required for airworthiness.

This could be Active Parking which means minimal preservation to keep the aircraft airworthy by regularly starting the engines and rolling back and forth to prevent flat spots on the tires.

There is also Long-Term Storage which can last for over 120 days and even take a few days to complete to ensure that the engine is preserved and the interior is protected.

The Best Way To Fly A Plane After It Has Been Sitting Idle

The Best Way To Fly A Plane After It Has Been Sitting Idle

If you are aware that you may not be flying properly for a few months, you should find some benefit from ground-running your engine every couple of weeks. This can help keep the engine happy and lubricated which should prove ideal when you do get out to fly. 

A ground run should be just below run-up power or considered at a fast idle. You may also want to try taxiing around from the run-up pad and back simply to keep the components moving and the wheel bearings running.  

A ground run should be beneficial to the plane’s engine and you should follow certain guidelines. The engine oil should protect against corrosion and a ground run can help spread that clean oil across the engine and lubricate various parts. 

Take a ground run seriously and treat it just as you would any flight including the preflight as if you are taking it up.

If any issues have built up over the time the plane has sat idle then you may be able to pinpoint them during the ground run which can mitigate any serious issues early on.

Just like you would a car, you should look to preheat the engine gently so it will not be shocked. Gradually get the engine oil up to a running temperature and this should rid the engine of any moisture.

This should be a standard operating temperature which should be right in the center of the green arc and then kept there for at least 20 minutes.

That time at operating temperature is crucial as a shorter duration can cause wear by combustion blow-by which leaks around the piston rings that contain water. 

You should also be looking to perform a ground run that is long enough to recharge your battery. The ammeter or load meter should tell you whether the battery has been replenished before shutting down.

For this to happen, the engine needs to run at a sufficiently high RPM which should mean a fast idle at a long enough duration, perhaps half an hour to 90 minutes depending on the outside air temperature.

Ideally, only use around 50 to 60% of your engine’s maximum rated power during a ground run to allow the engine to burn cleaner. 

Final Thoughts

There may be situations where you cannot fly your plane and simply have to store it. Though this is not ideal for a lot of aircraft, knowing how long you should leave it and what to do after is important.

After all, you should treat a plane’s engine just like any if you want to maintain it and prevent malfunction.

Frequently Asked Questions

Can Short Flights Or ‘Quick Hops’ Be Considered Detrimental To An Engine?

Yes, while you should not leave your plane sitting for too long, it is important to get the oil temperature up. An airplane should ideally be flown regularly, once a week is the best policy but certainly over once a month. 

However, how long you fly the airplane is also crucial as you want it to fly long enough to burn off any moisture that may exist in the engine while it has been sitting idle.

A ‘quick hop’ or a flight that only lasts for 20 minutes can generate even more moisture in an engine without allowing any to be burned off. 

What Is Tarmac Delay?

There are occasions when your engine will be running but you cannot fly which you simply have to deal with as a pilot. One of those situations is known as Tarmac Delay and it can be truly frustrating.

This is where an airplane on the ground is forced to wait before takeoff or after landing while the passengers have to remain seated. 

At a busy airport, you could be waiting quite a while due to Tarmac Delay and that time can become annoying to you and your passengers. 

Jacob Stern
Latest posts by Jacob Stern (see all)