Re: Does heating oil go bad?
Heating oil is basically diesel fuel, with red dye added to show that you haven't paid highway taxes on it. (Don't put it any on-highway vehicle, you could get hit with huge fines and jail time.)
Over time, diesel fuel can start to gel as volatile compounds are lost, and that can clog filters and nozzles. But that takes many years; 18 months should be insignificant. As long as it's still liquid, you should be OK mixing it with fresh fuel and using it. Oil burning furnaces are usually more tolerant of bad fuel than a diesel engine would be.
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.