My VO gathering and filtering goes on in the winter but living in Minnesota I am unable to use it as much as I do in the summer so it starts to back up. It is fully ready to pour into my tank but has been sitting for about 8 months now. Is it still good? Thanks, Joe

If it's kept dry, and was well filtered, and hasn't been exposed to too much air, then it should only need a final filtering to use in your vehicle.

If it was stored in conditions that might have accelerated deterioration, then it should be checked.

Conditions that accelerate deterioration: food residue, water, sunlight, air, heat, rust, bare iron, copper, or brass. In the most extreme case of all these things being present, veg oil will start to oxidize, polymerize and grow bacteria within days, turning into a stinking, viscous goo within a month.

Conditions that slow deterioration: purity, dryness, darkness, airtightness, cold, plastic container. Really well stored veg oil can be kept useable for a couple years. In theory, if kept frozen, it might last indefinitely.

Most storage conditions are somewhere in the middle. If it was dried and filtered, then stored in a sealed plastic tote or drum over winter, it might have a little sedimentation or high melting point fats to avoid on the bottom, but will otherwise be ready to use as fuel.

To test it, first check for a "paint" odor. That will appear before the viscosity starts to increase. That odor is the result of oxidation and polymerization starting.

If it smells rancid ("RDV", or Rancid Dog Vomit), it had water present and has a bacterial growth. It can probably be salvaged by drying and filtering. Water washing or mist washing seems to be a successful treatment to strip out the nasty parts.

To check gross viscosity, half-fill a pop bottle with the suspect oil, and half-fill another bottle with fresh oil AT THE SAME TEMPERATURE. Tip both upside down, then right side up and observe how quickly the oil flows back down. If the suspect oil is a lot slower, then it's probably worth trying Tilly's Viscometer (hint - it uses a pop bottle with a hole in the lid, and a watch that counts seconds). I doubt that a single winter's storage will harm your oil. These are just suggestions in case you are concerned that your oil might not be up to yoru own standards.

Finally, I've used "old" oil to make into biodiesel, with no obvious problem. Even high-viscosity semi-polymerized oil makes perfectly good biodiesel. The unknown aspect is how long the biodiesel will last in storage - it might have an accelerated aging effect.

In early winter, I dry and filter oil for storage in a plastic tote. In mid-winter, I dump the collected, dirty, wet, semi-solid grease into a drum in the shade, where it stays solid until spring. Solidified wet dirty oil keeps just fine, until it liquifies, then the clock starts ticking again.

Cheers,
JohnO

Joe - Go ahead and use it. I've used oil up to 3 yrs old and if stored well, no signs of turning rancid. Settled/dried and filtered and you're good to go.

8 months is a drop in the ocean. I use oil older than that ( on purpose) every tank full.
I concur with keeping the oil in an airtight container and making sure it is dry at least before you use it.