Gas Guage vs Fuel Tank

I've got a head unit that has a fuel gauge as well as the standard one in the instrument cluster. The two gauges, which my guess are feeding off the same sensor are never in agreement. I wouldn't think the truck has two fuel amount sensors in it. With a full tank the gauge on the instrument cluster reads above the full mark while the gauge in the head-unit reads 90%. At about half a tank on the instrument cluster gauge, the head-unit gauge is about 45%. I take both the gauges with a grain of salt and like a lot of folks in the frozen northlands, keep the tank at half or above in the winter months.

I take the fuel and range amounts shown on either gauge with a grain of salt and just use them to approximate when to fill-up versus trying run the tank down to the very bottom.

 

Just to make sure I understand this ('cause its new to me). The fuel pump, located in the tank, is submerged in the fuel, and with a fullish tank the fuel cools the pump better than if it were only partially submerged, which happens in low fuel situation. Is this correct?

 

…Yes, I have read through chunks of the manuals, which I have downloaded on my iPhone for reference, but reading them takes time (and understanding them takes experience).

Let’s face it, I look for answers as I go and missed the bit in the manual on the fuel gauge (or didn’t understand what I read).