Offshoreonly.com - Mercruiser 7.4 LX MPI Intermittent Overheat

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Mercruiser 7.4 LX MPI Intermittent Overheat

I am having an issue with my 7.4 LX MPI intermittently overheating. I purchased the boat about 8 weeks ago with a bad transom. I had the transom replaced and got the boat back for Labor Day weekend. While in the shop I had them replace the impellers while the motors were out of the boat. I ran the boat for a couple of hours last Friday with no problems. I returned to the water on Saturday and ran it for a couple hours without any problems. Saturday evening while headed back to the launch the motor climbed to about 210 degrees. I took the boat home and replaced the thermostat I went back out Sunday and put 70 miles on the boat between Sunday and Monday with no problems. So then yesterday we went out motor ran great again. In the evening when we headed back to the launch I noticed the motor climbed again to 210. At idle the boat runs cool and the motor only overheats at cruising speed. I am stumped anybody have any thoughts?

I agree to backflush - I would also check the wires on the temp and temp sending unit.

Most likely there is a little something that's blocking the water flow

all the best

3pointstar

Rule #1 is to check frt (inlet) of oil cooler. Pieces of impeller and other misc things have a habit of getting stuck there...right against the inlet of the tubes.