I cant believe your "mechanic" is mis-informing you so much. I would stop listening to him.
Ill just leave this here.
http://iqlearningsystems.com/ethanol...cteristics.pdf
and the highlight.
INCREASED ENGINE LIFE: Ethanol has a very high MON octane rating, allowing engine
builders to run higher compression ratios without fears of destructive detonation. It also has
a very high Latent Heat of Vaporization, so the engine is cooled far better than one running
on gasoline. This lowers bottom end and oiling system temperatures substantially.
Then ask him why General Motors and all major car manufacturers would design engines to run solely off of a "corrosive" fuel like E85 to damage the engine. Thats called a flex fuel vehicle. We owned one and I would purposely find E85 to run a tank of it about every 5 tank fulls to clean the fuel system out and more notably to clean the cylinders out. Ethanol removes carbon build up from the engine that is caused by petroleum based fuels. aka 91 octane pump gas.