My car ran out of petrol (faulty gauge) and the only spare fuel I had in the boot was a 1:50 premix for my boat’s two-stroke outboard engine. Could I have used that to get me to the next station? Harry.
Yes. Your initial restart might take a moment longer and you might not get the sweetest smelling exhaust fumes, but the car’s four-stroke petrol engine would probably run well enough on a 1:50 mix to get you to a petrol pump, and in many engines would cause no immediate harm and not need purging.
If you don’t put too much mix in the empty tank, by the time you completely refill with clean petrol the proportion of oil would be negligible and would not cause long-term carbon deposits in the combustion chamber.
But that solution is still an “emergencies only” option. Ensuring the fuel you use is as pure and clean as possible is an important discipline – especially with diesel engines.
Oil and petrol are completely miscible. Your boat’s 1:50 mix is relatively lean on oil. The tiny “seagull” outboards ran on 1:10 (smoked a lot and lasted forever). Other two-stroke engines like strimmers, chainsaws and lawnmowers run on mixes between 1:20 and 1:30.
Some people occasionally put a bit of oil in their petrol when they fill (but with something nearer a 1:100 mix – very lean) in hopes that it will give better lubrication to the fuel tank and delivery system, and perhaps a slight gain in power.
Those side effects are somewhere between improbable and unnoticeable in ordinary motoring. It is most unlikely to improve fuel economy, as the nature of the fuel burn that spark-ignition petrol engines are designed to optimise would be slightly compromised.
Contrary to myth the mix is more likely to reduce than increase the fuel’s octane rating, whose job is to resist (!) spontaneous combustion until there is a spark (in contrast to diesel engines which measure a “cetane” rating that encourages combustion under pressure...without a spark).
Octane and cetane are not only equivalents - they are opposites. The “power” potential of different fuels is a measure of their latent energy, usually calibrated in British Thermal Units (BTUs) or metric joules.
