I was out on the water last weekend and noticed my port temp gauge acting weird. Started out fine, warmed up to 170 degrees, idled around for a while and all was good. Then rather abruptly, the gauge went to all the way to cold...slowly climbed back to 170 and repeated the process over and over. It never climbed past 170, the raw water was warm coming out the exhaust, there was no signs of overheating. Everything was fine except the way the gauge was operating. New bravo pump housing and impeller, circulating pump, thermostat and risers & manifolds last year. It's been acting fine otherwise. Any ideas? Temp sending units? Gauge?