An infrared temperature gun scanned over the side of the tank will detect a surface temperature change between the transition from liquid to air/gas inside the tank. Seems to work best in the morning after an overnight change in ambient temperature.
Yup! I use one. For me, I found that best time to tell is after engines have run for an hour or so; tanks are close by so their top area with vapor becomes notably warmer than lower portion with liquid. Still, I'm not always sure I'm getting accurate readings even then, and, its a pia to stop and open salon sole in midst of cruise for fuel-level check. In morning I'm suspect of readings; temps seem to have equalized. Keeping tanks topped off is always a sure way to have ample fuel... but with today's ethanol %age and fuel separation factor I'd like to not leave full tanks for too long a period. 2013 and likely 14 are reduced boat-time due to our 90yr Matriarch needing family company and care. Boat's docked 100 miles away in covered berth and great swimming areas; we go out for days each time... if near-by I'd/we'd be on her way more often for day jaunts... even with Nana’s needs.
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