this is my first post on the forum. i have been lurking for a couple years and i have always been able to find answers by searching. i have been chasing a possible overheat issue on my boat for about a month. i have a 1991 wellcraft eclipse 233 with a mercruiser 5.7 v8 and alpha one outdrive. back at the beginning of the boating season the boat developed a vibration at low speeds when turning. it ended up being a bad u joint on the drive. i replaced both u joints, the gimbal bearing, all 3 bellows and an impeller since i had everything apart. i only replaced the impeller vane and not the upper and lower housing. everything looked like new in the housing. fast forward 2 months later, i was out cruising along and i happened to glance down at the gauges and i saw the temp gauge at almost 200 degrees. at the time i was at 4200 rpms around 33 mph. i backed down to about 3000 rpms and the temp came back down to around 150. if i went over 3500 rpms it started to climb again. first i tried a new thermostat and it made no change. then after reading on various forums and asking a few local boat mechanics everyone suggested that i replace the impeller again along with the upper and lower housing. i did that last week. when running the boat above 4000 rpms now, the temp gauge slowly starts to climb and levels off around 170-175 degrees, but when i back it down around 3000 rpms the gauge goes back down to 140-150. today while i was running it i monitored the engine temp with an infared laser thermometer. nowhere on the engine did the temp get over 140 degrees while above 4000 rpms while the gauge was showing around 170, but as soon as i back the throttle down the gauge goes back to 140. having the thermometer directly on the water temp sensor it never showed above 140. everything is pointing to a bad gauge but it makes no sense that it is only inaccurate above 4000 rpms. the water temp sensor is brand new, i just put it in today.
thanks for any help at all. this boat is driving me nuts!!!
thanks for any help at all. this boat is driving me nuts!!!