I found old steel jerrycans holding ~50 gallons (~200 liters) of heating oil. They were stored in a place where temperature can go below -5°C.
Is it safe to use it for heating?
If so, should I mix one can at a time into the main tank (in order to maximize the dilution of the "bad" oil into the "good" one), or should I pour everything in my nearly-empty tank (to avoid wasting one full tank of "good" oil) ?
Should I filter this and how?
Thank you very much!
Storage temperature (especially in the low direction) does not matter much; cold would actually be beneficial.
If the cans were clean when filled and sealed, the fuel oil may be fine - if it has a biotic slime, it may be practically unusable, or at least require a lot of processing (biocide and filtering) before use. I think @FiascoLabs means (and what I know is) that old diesel (fuel oil - same thing, different taxes) WITH slime Bacteria is notorious for clogging filters. You also do NOT want to start a slime bacteria colony in your (presumably clean) fuel tank.
Clean old oil can be fine - folks have reported successfully using old caches (sealed drums) from WWII era 50+ years later.
I suppose the better safe than sorry approach would be to purchase some biocide and treat each can as if it were contaminated, give that time to work, then run it through a funnel with filter to visually examine the extent (or lack) of evident contamination. If it appears to be clean, proceed with use; if not, deposit at an oil recycling facility. If that seems like too much bother, proceed directly to the oil recycling facility.
