Quote:
Originally Posted by G.M.
After many days of test driving my 39 with a return line after the pump back to the filler neck. The line has a 1lb check valve and a .070 restriction hole after the check valve. Line used was 3/16" OD steel brake line. Driven in temperatures over 90 degrees the car ran perfect, never skipped a beat and could idle without any signs of vapor lock. If the fuel pump temperature gets over 125 degrees the vapor lock starts, at 135 your into VL. When the engine is running with the return line even at idle the pump remains below 115. My car is black and gets real hot in the sun. A 39 has poor fan circulation due to the low location of the crankshaft mounted fan. The air is pushed into the front of the engine with very little or no air over the top of the engine. At driving speeds the air created by forward motion go's through the full surface of the radiator with some air over the top of the engine. Another problem with the 39 is no area at the rear in the firewall area for hot air to escape. As a result everything on or near the rear of the engine gets to over 135 degrees. Insulating fuel lines, raising the pump, heat sinks and other heat transfer method do nothing to reduce heat. The only thing that worked was a high speed computer fan over the pump with a funnel like duct directing air on the pump. Heat sinks eventually get to the same 135 degree temp. The return line keeps the pump cool at any engine speed as long as the engine is running. I had 2 occasions where it didn't start on the first turn of the engine after sitting for a while in the sun and had to turn over 6 or 8 turns and needed to be choked. Then on a 94 degree stop for lunch parked in the sun it wouldn't start after 8 or 10 turns of the engine. I got out and the glass bowl was just about empty, I grabbed the laser thermometer and the pump was 135. I removed the air cleaner and shot some either down the carb and it started and with a few more shots picked up fuel and was running. I checked the pump temperature as soon as it started and the temperature was falling and went right down to 116. I don't think this situation would happen very often with the return line but it can. I just happened to think of a cooling fluid that comes in spray cans for cooling electronic components when looking for over heating problems. This would cool the pump fast and as soon as the temperature drops to in the 120 range the engine will restart. I know the electric pumps work but I just don't like them. G.M.
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GM i have used this exact type of routing fuel lines and it always worked to stop vapor lock. I it did not work on a flathead it must be a Ford defect.