I've been reading other posts about Inaccurate or Fluctuating readings of Liquid Filled Fuel pressure gauges that are mounted in the engine compartments due to engine heat. I want to know if even though the gauges Fluctuate because of the heat, is the Actual fuel pressure still the 12psi that it reads when the engine's cold? In Extreme Engine Heat my Summit Gauge shows fuel pressure readings as low as 7.5 psi but, the engine still runs fine at all times.

 

I would say it is the 12 you see when the engine is cold.

 

That is correct, the actual pressure remains constant. It's just that the fluid in the gauge and/or the gauge line starts to try to expand as warm fluids do. As they do expand the gauge shows less difference between the actual fp and the pressure of the fluid in the gauge. The gauge shows the pressure difference between the two fluids.