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Mercury 150 xri High Idle Overheating

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bshultzrn

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"A year ago I paid a mechanic

"A year ago I paid a mechanic $1100 to fix my motor...it would overheat at high idle...he found a hole in the divider plate, and a leaky head gasket. After the repair, the boat ran fine for 6 months. Now it's doing it again. At idle it runs at 140 degrees. At full throttle it runs at 140 degrees...but at high idle and planing speed 1200-2000 RPM...it runs hot as hell >180 degrees. I inspected the divider plate..looked fine...replaced what I thought was a leaky head gasket..and replaced the popet valve diaphragm, gasket and spring...still having the problem..boat runs great..clocks 63-65MPH and idles great...Water PSI 10-12 at full throttle...10 PSI at idle...I need help!!!"
 
"Blaine, the 140 degrees isn&#

"Blaine, the 140 degrees isn't totally out of whack - sounds close to about right.

Where you notice the high temp (if it's being measured accurately), in the 1200-2000 rpm range, at this point your thermostats should still be controlling the temp, with the bypass not quite kicking in yet.

So my question - when were the thermostats last changed/checked. They could be your problem (or part of it)..."
 
I changed both of them out and

I changed both of them out and even tried running without them...no difference...the idle temp is great...but it goes right up with cruising..but then cools of at WOT...also the water coming out of the piss hole is very hot when the temp gauge is at 180 degrees...one thing though that I noticed is that there is a "hook" at the back of the hull in front of the engine...which could cause turbulence...and the high pressure hoses may need to be replaced...
 
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