Regardless of what the dealership's mechanic had to say.... in all probability, that water pump could be five years old... OR... new when you bought it, however regardless of how old it is..... that water pump is weak, failing, and about to let you down. Your explanation of the problem is exactly how a engine acts when the water pump "starts to go" as the saying goes.

The engine is an excellent design, but as with anything mechanical... problems will eventually arise. It's just difficult to have someone local to handle the problem efficiently the first time around.

I suggest that you have a compression check and a spark test performed, either by your self (doesn't require rocket-ship mentality)... OR... by a trusted mechanic WITH you standing there watching.

Compression should be 100+ on all cylinders and fairly even on all cylinders.

Spark (with s/plugs removed) should jump a 7/16" gap with a strong blue lightning like flame... a real SNAP!

(Spark Tester - Home Made)
(J. Reeves)

Most auto part stores have "air gap" spark testers... OR..........

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

Hi Joe and thanks for your reply. I took the boat out this weekend after picking it up from the dealer. Within 7 minutes, the overheat alarm went off again. All in all, it went off 6 times in an hour. One thing I did notice, when I trim the motor up after I get on plane, the motor does NOT overheat. When I run the motor all the way down (not trimmed), the alarm will go off all the time. Shouldn't this motor be able to be run without trimming it up? If so, what does the mechanic need to do to solve this problem?

Normally it would be the complete opposite of what you've just explained, that is tilting the engine too high... near the surface, grabbing air.

I can only guess that perhaps the engine is tilting too far in and when full throttle is given, that extreme angle is actually raising the transom up... OR... something on the hull or transom is throwing a air pocket into the water intake area when at that angle.

When the engine is perfectly vertical, the cavitation plate just about the propeller being parallel with the keel..... where is that cavitation plate in relation to the keel at the transom... higher, lower... by how much in which direction?

Hi Joe.
I looked at the motor this weekend and the cavitation plate is about even with the bottom of the "V" of the boat. Maybe a tad lower but not by much.

Tom

When I first started off in the marine line with OMC, that's exactly where I was taught to have the cavitation plate... slightly below the keel at the transom, not to exceed 1"... 3/4" below seemed to average out for me.

Frankly I'm at a loss to explain the cause of your problem other than the possibilities I've already mentioned.

If the engine tilts/trims too far in which would result in the cavitation plate exceeding a parallel with the keel, that would have a tendency not only to push the boat forward but also to push the transom upwards to lower the bow quickly. Whether that would throw a air pocket into the propeller... I really don't know.

Joe,
Would it make sense to lower the motor one "notch" or hole to see if the issue resolves itself? Currently, the motor is mounted in the center of three holes.

Tom

During my last 12 years with OMC, I worked with a outfit in Tampa that specialized in fast Ba$$ Boats. I noticed the rigging department installed many V6 engine with the cavitation "above the keel at the transom. Rigging was not within my job description so I never got involved in any discussion of why a engine would be installed in that manner but I a$$ume it would be speed related. Why those installation setups did not overheat... I don't know.

In your case, if it were me, yes, I would drop the engine one hole just to see what happens.