I noticed that the previous owner of my 63 Coupe had condemned the Vapour return line (390 motor) by sealing it. Is this line necessary to be hooked up for proper functioning? Thanks.

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If you are talking about the smaller fuel line on top of the fuel filter housing, then yes, that is a fuel return line to the tank. It is not a necessity, but it does help with preventing vapor lock. 

Thank you Russ. What do you mean by vapor lock and what does it do? In the mean time I will start looking for the proper housing as the fuel housing on the car does not have the additional port to reconnect the hose.

Marcel, vapor lock is when the fuel in the fuel line becomes vaporize and blocks the flow of fuel. This happens in the engine compartment. The return line keeps the flow of fuel through the fuel lines and helps reduce the chances of vapor lock.

Depending in your climate, it may not be needed. Hotter climates tend to benefit from a return line.


Vapor lock is a condition that prevents you from being able to start the car caused by  a heat build  up in the engine to keep it simple 

My  64 gas return line has been disconnected for over 45 years with no issue at all effecting how the car performers 

My own opinion for what it’s worth is the return line is of no value  at all and not sure if it would prevent Vapor  lock  if that happened that I only experienced once I a 1952 Cadillac CDV that was my fathers 

I myself do not know of any other make or year cars that have the gas return line design  built into them but our year Cadillacs but that does not mean there are no others 

Your need to be stock above all could be a consideration depending on your own needs 

Your car and your call !


Thanks for the valuable information. The shop manual stipulates that super gas is recommended for fuel for the 63 Caddies. Now that was back in 1963. Is it safe to drive on regular gas now.  

Most of these cars will run fine on 92 or 93 Octane. Check out this Help Page link, listed under Octane for more info: http://6364cadillac.ning.com/photo/octane?context=user

Thanks Jason again great info.



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