Lincoln/Mercury Repair: cleaning fuel system, ford dealership, compression engine

Question
Hi Dinger,
  I read in one of your recent responses that you recommend "shell Premium" for cleaning your fuel system.  Would this work in a car that doesn't call for premium gas?  I have a 2003 Town Car, that calls for 87 octane & has a compression ratio of 9.4:1, and wondering if the burning of the combustion mixture would be as complete since the mixture never gets to the same pressure it would in a high compression engine. Or could there be any other adverse effects?
   
   My wife has a 2002 continental that calls for 91 octane & has a compression ratio of 9.8:1.  The owner of the Ford dealership where we bought the car said it would make no difference on performance or engine life using the 87 octane.  The service manager, same dealer, said he would use one tankful a month of 91 octane and rest 87 octane.  

     Would appreciate knowing your feeling on the above topics.

Thanks,
Harry

Answer
Hi Harry,

Yes, by all means and you will notice an increase in performance also. The 87 rating is a minimum octaine rating for your car. Not only will premium help clean your fuel system, but will clean the valves and cylinders as well. I must disagree with the service manager at your dealer in the respect the Ford gave it this rating for a reason and it does change perfomance, trust me! My owner's manual says that engine damage will occure if I use less than 91. I know as a matter of fact that using regular where premium is called for will cause damage to the engine. On the fuel door on your wife's car it probably has a warning label to use Premium only. Please remember my first sentence, 91 is the minimum octaine rating for her car.

One last note Harry, I have burned nothing but premium in my car and have tried many brands. My Navigator runs so good on Shell that I only use other brand's if it's an emergency. Citgo seems to be the worst. No, I am not on Shell's payroll! LOL Hope this helps. Happy motoring!