All Shell gasolines now have E10 mixed into it. One major problem is the gasoline will "expire" within a few WEEKS when left in the tank of a car. This results in poor running engine. Only fix for this is to drain the fuel tank and replace with "fresh" gasoline.

This is the exact same problem with my car. Since it is using Auto-LPG, the gasoline in the tank is not used up quickly, remaining in the tank of weeks to months.

Since you mentioned you rarely use those cars, it might be advisable to look for gasoline stations that sell non-E10 mixed gasolines. Currently I use Petron XCS since it doesn't have E10 (yet). I suggest you to do the same for those cars you have mentioned that you don't use often.

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You might also want to read the following thread:

E10 Ethanol and your engine [MERGED]
http://tsikot.yehey.com/forums/showt...=59222&page=48

Just back read it to the areas where it is useful for you.