Will it harm the engine running unleaded fuel in a leaded engine?
If it originally ran on leaded fuel, then it wouldn’t of come with a catalytic converter. If you did run leaded gas through a catalytic converter the converter would be ruined (in Ontario it’s an offence to use leaded fuel with a catalytic converter and an offence to run the engine even if you replace the fuel without repairing / replacing the cat). This clearly isn’t a problem though if the car was not manufactured with a catalytic converter. The lead was originally added to fuel as an ‘anti-knock’ agent. Some fuels (e.g., aircraft) still have this in their fuel, but in most parts of the modern world it has been completely banned for street vehicles. You can get additives you pour into your tank after the fact (as others have mentioned). When you go to fill your gas tank, you may notice that the nozzle doesn’t fit well either – that’s because unleaded fuel vehicles have a different aperture to prevent accidentally filling with leaded gas.
