OK, Carson, that idea grabbed me. Went right out and put my IR gun to work. (Unlike many, I have not had any trouble with my indicators.) (So far.) (Crossing my fingers while knocking on wood.) :
Sunny, Ambient temp = 79
Side wall of bay doors - white - of the MH was 95 in the sun - - 74 in the shade.
All tank contents were low. Might be different when fuller.
Propane- shady side: Gauge on tank reads a little over 1/4 tank. Inside indicator reads low. IR read 78.5 above level and 75 below. Agreed approximately with indicator and gauge. 3.5 deg difference, but sharply deliniated. I could tell where the top of the liquid probably was.
Water-shady side: Inside indicator reads low. Visual shows tank is about 1/6 th. IR reads 73.5 above and 71.5 below. Only two degrees difference. Might be different if there was more water. Doesn't matter as the water is visible through the tank wall.
Gray-sunny side: Inside indicator reads low. Should be low. IR indicates low. 73 above and 70 below. Note that on ths side, the higher temp is above the line, unlike the water temp on the other side. Not sure that's why, but it is different from the shady side.
Black-sunny side: Inside indicator reads half full. The yellow light is lit. 72.5 above and 70 below. The differential line indicates that the second sensor has just been submerged and should be lit, inside, which it is.
I like the idea. My differential is even less than Carson's, but repeated readings were pretty consistant and the line was fairly abrupt. I think this may work for some who are driven nuts by their indicators or have no indicators. Need more test results, from others, to add confidence but this shows promise.
Thanks, Carson.
Ray D ;D