Hi Mf,
I wouldn't put it into a car tank ,although I have used fuel like that in an old car with a carby if I was going to use all the fuel in the tank
that day.
I usually put a small amount on the ground and light it to see how it burns , if it burns I just use it in a Briggs 3.75 sprint with the primer
carby, if it doesn't burn you could mix it with 50 percent of new fuel and use it in the sprint 3.75.
Cheers
Max.