Thread: 500 Caddy/G Body Swap

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I found out a couple of things over the last couple of weeks, one is they are now using 10% ethanol here year around now. The cars that I have never had any vapor lock/heat soak problems with don’t like it very much, especially the heat soak thing. It hasn’t been bad enough so far to leave me walking, but it is aggravating. I think it’s a combination of the heat (a tad over 100 degrees) living 4500 feet and the poor gas. I remember reading a while back that they are proposing an even higher percentage of ethanol so I suspect things will only get worse.

Anyway this led me to start considering what besides the obvious things like fuel line routing, 1” Phenolic spacer and good fuel pump(s) I would need for this project. One of the almost sure cures I’ve used in the past is to run a return line to the tank so the fuel is constantly in motion and doesn’t have a chance to heat soak

I’m going to rebuild and use the original Q Jet from the Caddy so I took a look at it. One thing I had never really noticed on these before is that many have an aluminum soft plug located in a cast boss at the front of the filter housing.

I thought this would be an ideal place to put a fitting for a return line. I’m planning on running an electric pump located at the tank in conjunction with a stock mechanical pump on the engine. My thought is even in a situation where the engine is shut off and the fuel in the lines heat soaks, running the electric pump for a few seconds should clear any vapor and hot fuel from the line clear to the carburetor.

I went ahead and drilled an 1/8” hole in the plug and used a small body work slide hammer to pop out the plug. The resulting hole was just right to run a 1/4” pipe tap thru without any further drilling.