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Thread: 135 hp OPTIMAX overheating
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06-24-2016, 11:30 PM #1New Member
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135 hp OPTIMAX overheating
Hi all.
2003 135 OPTIMAX, 375 hours, pushing a 18' Boston Whaler. I'm getting high temp when running at low speeds (up to 175 degrees,@ 1500 RPM)
@ 1700 it drops to 120.
Two thermos today didn't change a thing. New impeller last fall.
Any good thoughts???????
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06-25-2016, 01:25 AM #25000 RPM
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use temp gun and narrow it down,l/r head or air pump?just impeller?after market pump?pinch a waterpump grommet?drop case inspect pump-th
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06-25-2016, 08:51 AM #3New Member
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OK
I'll start checking those out
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06-28-2016, 03:52 PM #45000 RPM
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If the engine cools down quickly when above 1600 rpm or so that's the poppet valve opening- so your high speed cooling system is OK. Overheating below 1600 rpm or so is usually caused by one of three things on an Opti. First is a bad impeller- or bad install on a replacement. Pressure at idle speed should be at least 1.5 psi on a new impeller(Opti's have a very low pressure cooling system at idle), and at least 1 psi on an old impeller. Second thing is failed thermostats- from clogging with dirt/weeds/etc. These are simple to just replace since it's a pain to blow them out and test them. Third thing is a clogged intake screen on the coolant hose going into the air compressor. Typically you have to drop the lower cowl to get to the fitting, which is close to the compressor housing.
Doug
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