Yes, it is a simple concept. The fuel tank will act as a partial heat sink, more so when it’s cold. But over time the tank will heat up and lose effectiveness. It will take more time with a full tank, but none the less it will heat up and not do much to cool the fuel.
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Take a look at the fuel cup I’m speaking about. The return line (right) literally dumps hot fuel right back into the pickup (left) while being supplemented by fresh fuel from the bottom. The ratio of fresh fuel to recycled hot fuel is determined by the flow rate of the pump, and unknown:
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The cup clips into the sending unit/bowl cover:
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And then the bowl covers the entire assembly:
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As you can see, the little cup is the biggest enemy to the fuel tank heat sink effectiveness. If you separated the return line and dumped the fuel elsewhere in the tank the concept would work better. But then you’d have fuel starvation problems when the tank runs low.
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I’d love to see your extensive testing/data linking fuel tank volume, and fuel temperature, while also noting air temp, and engine run time. Fuel volume WILL certainly have an effect, but it will not be substantial. I’d be interested to be proven wrong or right either way as these are just my own observations.
(Please note that although this IS a factory Duramax fuel tank pickup assembly, I have modified the mounting flange and hoses to suit my installation. That's why it looks strange)
