Classic/Antique Car Repair: Motor Oil, storage environment, motor oil

Question
Mr. Bullock,

My question pertains to motor oil, and specifically old, never used oil.  After my dad passed away I was cleaning out his garage and found 2 cases of Castroil GTX motor oil, one case was 10W-40, and the other 20W-50.  I know this oil is at least 10 years old, and probably a lot older than that.  

Does motor oil have an expiration date?  These cases are unopened so I would like to either sell them or use them, but I really don't think I could use the 20W-50.

What is your opinion?

Thanks,
Gary in WV

Answer
Hi Gary:
Most oil companies recommend the shelf life of oil to be 5 years.
However, a lot depends on the storage environment. In a controlled
storage where the temperature and humidity remains constant, oil can last
indefinitely. However, the changing conditions in a standard garage
over many years and seasons will cause the oil to eventually break down.

If it was kept in a standard garage under the changing conditions of winters,
summers, snow and rain, it's a pretty good guess it is bad, but the only way
to know for sure is to open it. You will most likely find the 20W-50 in better
condition than the 10W-40, because it can withstand a higher degree of heat and cold.

Even if it looked good, you wouldn't want to trust it in your car engine,
but maybe an old lawn mower.