Narrative:

Aircraft left [departure airport] with 104 gallons [of] fuel on board (6 hours). Landed at [first destination] after [a] 40 minute flight. Departed for kdpa with 5 hours 15 minutes fuel on board. Flight plan was for 3 hours 45 minutes flight to dpa.conditions for dpa at arrival were forecast to be above minimums. [A nearby alternate was selected]; which was forecast to be MVFR upon arrival.actual flight time to dpa was 4 hours 6 minutes; which was 20 minutes beyond plan. The plane would burn less than 5 gallons of fuel at that time; since I pull back on the power upon nearing destination so as to not shock cool the engine.prior to receiving vectors for intercepting ILS 2L for dpa; the mvp-50 engine monitor gauge was flashing 0.0 gallons; and the starboard side gauge was flashing 4.5 gallons. My calculations for the flight time was that we had 17-19 gallons of fuel left. The mvp-50 was showing 20.5 gallons left in total.I intercepted ILS 02L and descended to 2500 ft. To spnce. After spnce I started descent to 1500 ft. I thought I saw the REIL and kept descending to 1350 ft.; shortly after which the tower informed me that I had descended below minimum. I then lost sight of the runway REIL.I was extremely stressed because of the conflicting information I was receiving from the fuel gauges and felt I needed to get down. I informed the tower that I needed to get down quickly; because the gauges were indicting I was very low on fuel. I asked for a circling approach and the tower gave me instructions to climb to 3;000 feet. With a heading. I was passed over to ATC.when I switched over to ATC; the controller asked if I needed help finding another airport. I informed him I was low on fuel; and asked if he could direct me to an airport that was well above minimums. ATC started giving me alternate airports; and then I spotted a sizable opening in the clouds; and asked if he could point out airports in that vicinity. He gave me a new heading and 2 airports. I spotted the second airport visually and proceeded to land there in VFR conditions.prior to leaving 2 days later; I had the general manager of [the diversion airport] stand with me while I fueled the plane to the tips. The plane took 94.6 gallons; which meant that there were 10 gallons left in the plane upon landing (usable fuel capacity is 104.6 gallons). We flew 16 minutes from dpa; which would have consumed about 4-5 gallons; which matched up perfectly with my calculations.

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Original NASA ASRS Text

Title: M-20K pilot reported low fuel level indications causing a descent below minimums on approach.

Narrative: Aircraft left [departure airport] with 104 gallons [of] fuel on board (6 hours). Landed at [first destination] after [a] 40 minute flight. Departed for KDPA with 5 hours 15 minutes fuel on board. Flight plan was for 3 hours 45 minutes flight to DPA.Conditions for DPA at arrival were forecast to be above minimums. [A nearby alternate was selected]; which was forecast to be MVFR upon arrival.Actual flight time to DPA was 4 hours 6 minutes; which was 20 minutes beyond plan. The plane would burn less than 5 gallons of fuel at that time; since I pull back on the power upon nearing destination so as to not shock cool the engine.Prior to receiving vectors for intercepting ILS 2L for DPA; the MVP-50 engine monitor gauge was flashing 0.0 gallons; and the starboard side gauge was flashing 4.5 gallons. My calculations for the flight time was that we had 17-19 gallons of fuel left. The MVP-50 was showing 20.5 gallons left in total.I intercepted ILS 02L and descended to 2500 ft. to SPNCE. After SPNCE I started descent to 1500 ft. I thought I saw the REIL and kept descending to 1350 ft.; shortly after which the tower informed me that I had descended below minimum. I then lost sight of the runway REIL.I was extremely stressed because of the conflicting information I was receiving from the fuel gauges and felt I needed to get down. I informed the tower that I needed to get down quickly; because the gauges were indicting I was very low on fuel. I asked for a circling approach and the tower gave me instructions to climb to 3;000 feet. with a heading. I was passed over to ATC.When I switched over to ATC; the controller asked if I needed help finding another airport. I informed him I was low on fuel; and asked if he could direct me to an airport that was well above minimums. ATC started giving me alternate airports; and then I spotted a sizable opening in the clouds; and asked if he could point out airports in that vicinity. He gave me a new heading and 2 airports. I spotted the second airport visually and proceeded to land there in VFR conditions.Prior to leaving 2 days later; I had the general manager of [the diversion airport] stand with me while I fueled the plane to the tips. The plane took 94.6 gallons; which meant that there were 10 gallons left in the plane upon landing (usable fuel capacity is 104.6 gallons). We flew 16 minutes from DPA; which would have consumed about 4-5 gallons; which matched up perfectly with my calculations.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.