Chilling a Gasoline Return Line.

Here is an interesting scenario. On rainy days or mornings, my fuel gauge reads significantly higher than warmer days. Where I live a cold day is actually 27 Celsius.

Could it be that the lower temperature effectively lowers the vapor pressure of the gasoline in the tank? Therefore there is a better ratio of liquid to vapor during those cool times?

My car tank is 45 litres however when I full up from empty, the most I can put is 33 litres. I apparently have 12 litres in reserve and at 12km/l fuel economy, I can drive significant distance in my island home using that reserve volume. I want to be able to register more volume on my fuel gauge without having to modify the fuel sending unit.

Also, the vapor vent line has been clogged for the past 10 years. I have tried to fix it but it is permanently clogged due to a defective roll over valve in the fuel tank.

I want to get more fuel consumed between fill ups. Here is my experiment to lower the vapor pressure in the fuel tank without introducing liquid or vapor leaks.

This line is connected between the fuel pressure regulator and the return line to the tank.

The suction line on my car's air conditioning is very cold and gets as low as 8 Celsius within the engine bay.

For the purpose of this experiment, I used a length of aluminium tubing to allow return fuel to flow.

I used cable ties to secure the tubing to the air conditioning suction line. This way there will be some heat exchange when the air conditioning is running.

I turned on the engine to verify all connections are liquid tight. I used a piece of paper towel to check for leak at each new connection I made.

Using my seek thermal infrared camera, I started the engine and measured the return line temperature after 10 minutes. It read approximately 33 Celsius.

Putting the air conditioning on, I tried measuring the same line after 10 minutes. Due to thermal bloom from a nearby power steering engine hose, it was difficult to get a good reading. The tubing however got cold to touch but since it is shiny, my thermal camera is useless to measure it. The air conditioning return line got predictably cold.