It is except you can't always trust the refiner, distributor, or the service station to deliver actual #1 or #2 for that matter. They are not against mixing or diluting to move excess or enhance a deficit.

 

It's used more as a heating fuel (furnace).

Good reading ~ http://en.wikipedia.org/wiki/Fuel_oil

 

Mine was over 3/4 tank when it gelled at -17. The fuel in the filter was liquid, I couldn't get it to the filter, but I dumped hot water over the filter, so I might have warmed it enough to put the waxes back in suspension.

To get mine running I pulled the filter line off the turbo, unhooked the heaters, hit the starter with a wrench and feed it ether. I'd say it might have taken 30 seconds to prime, I'm not sure just when it took, I think when it revved up for a moment. If you do it, don't go shooting a full stream straight into the intake. Start it cranking, then shoot a light stream across the opening and increase it til it runs.