Although motor oil has a viscosity which would seem to make it suitable for chain use. the molecular structure of engine oil is designed to resist high sheer loads in an engine. On a chain you do not have sheer but rotational friction inside the roller at the pin. That is actually the place that the lubrication is necessary. The very reason why chain lubricants are made to penetrate is the outside needs no lubrication.
Remember engine oil is designed to film away from components to remove dirt and impurities which are taken to the filter as such your chain will likely fling it away, along with any lubrication properties.
Simply not a good idea, they are designed for different purposes.
UTTER BOLLOX!
Engine oil will do a perfectly good job of lubricating your chain. It does however have a big undesireable side effect. It is sticky! Sticky in a way that even after your engine has been parked up motionless for a few weeks there is still an adequate film covering your engines internals to provide some level of protection at start-up. This means that it will attract and hold any dirt particles that come into contact with the chain. Engine oil holds contaminants and carries them to the filter by FLUSHING, not by being so p*ss thin that every drop runs to the sump. Also, if you are flinging the oil off your chain then you must have a pedaling cadence of more than 9,000-10,000rpm because engine oil is designed to work at such high rotational velocities.
In my experience car engine oil is a good chain lubricant for an MTB that is exposed to lots of mud and water as it does the job but is eventually washed/carried away by the mud and water. When used on road bikes I found it to simply accumulate any muck from the road, which builds up to leave a very gunky chain. This is where a specific cycle chain oil is best.
