Guys, I've said it before, but air in the heater puck is not what ruins the heater. It is a PTC (positive temperature coefficient) material heater coil, which means its own resistance increases in proportion to its own temperature. It does not care if the substance surrounding it is air or fuel! As it increases in temperature, the current flowing through it decreases and the coil's temperature levels off, no matter if you have it sitting on your workbench or submerged in fuel. Faulty manufacturing at the terminals is what causes overcurrent and burning.

Yes, dissection is in this unit's future. I'll have to see about getting the picture hosted...

FYI, the fuel heater is solid-state so the foregoing argument is null - consists of two lead-in wires crimped to two aluminum plates immersed (hopefully) in Diesel fuel - between the plates and held by simple dimensional tension are three solid-state 'coins', with specific coefficient of temperature properties, which heat when dc current is passed thru the coins via the wire\plate junctions - high-resistance when warm, low-resistance when cold, the coins not heat above ~45deg - the failure is in the two joints where the aluminum is crimped around the heat-proof wire - deterioration results in a resistive area(s) prior to the designed temperature-coefficient resistance heater coins between the plates, a resistance(s) which has no temperature coefficient, therefore proceeds to merrily toast the thermo-plastic surround, compromising the hermetic seal - if the designed plate-to-coin contact tension fails due to aluminum warpage, another non-tc resistive junction(s) develops, resulting in even more heat thru the aluminum plates to the aluminum-crimped lead-in wires - failure appears to be a design function......................

True, but catcrd musta missed it.................