How long is too long for oil/fuel?

Looking for some info on how long is too long for oil to be sitting before you should change it, even if it only has a couple hours on it?

Say you did an oil change and didn't fly it afterwards - when would you consider the oil bad? What's driving that?

What about 100LL?

Thanks!

WingnutWick said:

Looking for some info on how long is too long for oil to be sitting before you should change it, even if it only has a couple hours on it?

Say you did an oil change and didn't fly it afterwards - when would you consider the oil bad? What's driving that?

What about 100LL?

Thanks!

Click to expand...

Oil is pretty cheap and it will take about 5 mins to remove it via the dipstick with a vacuum remover, either store-bought or a DIY (youtube vacuum oil extractor). If there is so little time on it no need to change the filter. If less than 6 months I wouldn't worry about it, but it does depend on humidity and what it looks like on the dipstick.

100LL - depends a lot on humidity where you are, and then your engine type, type of airport, flying someone else or alone, etc. Draining tanks is not that hard, but a hassle. 100LL is supposed to have a shelf life of about a year under ideal conditions. Less than ideal conditions makes you a test pilot.

What is it about the oil that goes bad when sitting in the engine vice the original oil container?

Who cares about the oil and gas when the engine is rusting away?

Oil goes bad

One main difference, is oil in an engine has an unlimited supply of new oxygen coming in contact with it, where as oil in an unopened container doesn’t. This oxygen interacts with oil additives, oxidizing them, or “using them up”. Oil with depleted additives no longer does its job of not only lubricating, but cleaning. There are also additives that counteract or neutralize the acids formed from combustion products. These combustion products interact with water to form the acids. These acids can corrode the components inside the engine. The water in the air, and the higher the humidity of the region the engine is in the more water there is in the air, the more water there is available to interact with the oil to make acids. These are some of the main reasons oil is recommended to be changed at six month intervals when inside the engine, whether the engine is run or not. Oil stored in an original unopened container, on the other hand, is good for many years…
Jim Baker
RV-6
N699JB
CFI-IA

100LL should last 1-year. Lycoming recommends oil changes every 4-months regardless of hours flown.

Oil manufacturers typically put a use by date on the oil they manufacture. Sometimes it is on the container or the cardboard box. IIRC, Aeroshell is 4-years use by date after manufacture.

Thanks all!