I ran out of oil in my home, and a plumber friend said that I could add diesel from the gas station while I wait for my oil delivery. Is he right?
Yes, no2 heating oil is pretty similar to diesel. Just less clean and usually dyed red.
So yes, it's ok to put diesel in your oil tank.
Yeah, it's perfectly fine to put diesel in your oil tank, but for legal/tax reasons, it's not ok to put home heating oil in your diesel engine
Yes, diesel will work fine in an oil heater.
But don't try to put heating oil in a diesel vehicle.
It's illegal and will get you slapped with a $10k fine if you get caught.
Heating oil has a horrible cetane rating (in addition to lack of detergents and poor lubrication properties, and possibly higher sulfur content) and will make your engine run horribly and may damage it.