Using gas mixed with oil or old gas in a car

I have gas/oil 50:1 mix leftover from summer boating (2-stroke outboard).

Can I use this mix up in my car over the winter at a ratio of of say 1/2 gal gas mix per tankful of regular?

Will this lead or 1) excessive smoking 2) carbon buildup 3) something else?

Same question for some old gas/oil mix that has been sitting in the shed for >20 yrs.

Same answer: no.

Why risk screwing up your modern car with oil in the gas…ore even worse, with oil in 20 year old gas? Oxygen sensors and catalytic converters do not take well to burning oil. And engines don’t run well on 20 year old gas.

If you have a very old Saab (2cycle) or an East German Trabant, yes you can. For any other car this is not only illegal, but a really stupid idea to try to save a few dollars. Here we take it to the local landfill which has a big tank labeled “old gas”, as well as a “used oil” tank. If the gas is not suited for your 2 stroke outboard next spring, it is certainly not suited for your 4 stroke car now. Read your instruction manual, and if it calls for oil in the gas, you can do it!!!