Groundbound,
In any C150/152 or 172, IGNORE the fuel gauges. I mean it!! On this thread somewhere I described how I took out a club C152 that was close to empty after I was told it had been filled after every flight. The gauges were showing over half full. I recently got a share in a C150. We filled it completely with fuel, and I was shown that one gauge showed three-quarters full and the other a quarter full!
It made the point for me - you cannot rely on these things AT ALL! As far as I remember, they work by float thingies in the tank, and these can stick...in virtually any position. Hopefully someone will tell me if I'm remembering that wrong, but the bottom line is: IGNORE THE GAUGES!!! Work out your fuel by some other means, or fill up completely if weight and balance means you can.