I have a 1989 Mariner 100hp with a 16 pitch prop. Standard operating RPM 4800 to 5300. I have been dealing with an over heating alarm that only goes off when I am up on plane and running at 4800 rpm or higher. In order to reach 4800 rpm or higher I have to trim the engine up a little bit to gain that extra speed which is normal. Since I started getting this alarm at 4800 rpm or higher I have replaced water pump and bell housing, thermostat and poppet valve, and moved my transducer on the transom farther away from my water intakes. I do not however get an over heating alarm when I run 3/4 throttle while trimmed all the way down running at 4600 to 4700 RPM. I am running out of ideas as to what may be causing my issue, until the other day. I'm wondering if my engine is mounted too high on the transom. To the point that when I go full throttle and trimmed out that the water intakes are basically being blocked by the hull or the hull is creating cavitation with my water intakes sucking in small air pockets thus creating an over heat alarm under these conditions. Below are some pictures that I had recently taken. What do you think? I have two spots that I can lower the motor thus lowering the motor about and inch and a half to two inches. Does the engine look like it is mounted too high in conjunction with the bottom of my hull?
I bought this boat last year and the previous owner replaced the entire transom bracket. Im wondering if the knuckle head re mounted the motor to high...
I bought this boat last year and the previous owner replaced the entire transom bracket. Im wondering if the knuckle head re mounted the motor to high...
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