Engine overheat only in neutral

[frankpiz]

I have a 2006 maxum 2400 sc3 I just got it. The boat has 91 hours. When I went on the sea trial it ran at a constant 175 degrees. when I got it home it would overheat at idle on the muffs or in the water. I haven't started troubleshooting yet but does anyone have any input I would appreciate it. Its has a 5.0 MFI engine

[Tomd8950]

Try replacing the raw water impeller.

[frankpiz]

Thanks thats #2 on my list first Im going to check the thermostat and I've been reading about a check valve possible in the thermostat housing.

[mmwjr]

Interesting as seldom does it over heat at a lower rpm as opposed to a higher rpm.

Are you judging this by the helm gauge or audio alarm?

I like troubleshooting with a handheld IR temp sensor to verify readings.

[frankpiz]

When I went on sea trial not a problem. Took it home 1 week later put rabbit ears on started to overheat, put it in the water it overheated at dock. the gauge and alarm indicated . turned it off waited for it to cool down then took it out for the day above 1000 rpm steady 175 degrees. It only overheats when I put in in neutral and rpm drops to 600. Im going to get an IR sensor.

[Phillbo]

Time for a new impeller. Replace it before it shreds and becomes a bigger issue.

[mmwjr]

I would start with the impeller as others have said.

I would not recommend running it at high rpms even though its not overheating as if vains break off they will clog the system and result in more issues plus if it just plain fails on the water you could toast the engine.