What happened?

C

c-ness

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C Dory Year
2002
C Dory Model
24 Tomcat
Vessel Name
C-weetness
On the way home from Orcas Island to Bellingham today we came into Bellingham Bay and experienced the usual 2-3' following seas on a flood tide. Even though the Tomcat doesn't need much trim I decided to trim up the bow. After a minute or two the overheat alarm came on and the rev limiter took over. I shifted to neutral and after a couple of minutes i started up again, but the overheat alarm came back on. I adjusted the trim back to a more neutral position and limped back to Hilton Harbor at 8mph. As I approached the dock I tried the motors again and they revved up ok. What happened? Did I cavitate even though the engines seemed to be peeing ok? The seas were coming over the swim step and up the back of the Yammies.

Thanks!
 
Sounds like you will need a new thermostat. Easy to replace. I now carry a spare.
 
Was only one of the two motors overheating? If so, you could have picked up a plastic bag over the lower unit and water intake, which later fell off at lower speeds in the harbor or when you went into reverse.

On the other hand, if you really tilted the engines back a lot to lift up the bow, the water intakes could have been tilted up out of the water stream, and sucking air in the choppy conditions. Air intermittently in the cooling system might give you a continuous "pee" stream depending on the plumbing geometry, but not cool the engines properly, with the air/water mixture going out the underwater exhaust port unseen. At least, I think that's possible.

Joe. :teeth :thup
 
It depends on how much "Trim up" you gave. As you come on a plane, the boat rises, and the intake is more in a turbulent flow pattern. I run outboards trimmed up in shoal water, but never on a plane. I always watch the cooling water flow carefully.

After a high temp alarm--take the boat to an idle, trim the engines to mid range, and put them in reverse. It is not unusual to get a small piece of weed or kelp (or plastic bag) over an intake. Look to see if there is any debris. I have had this happen many times. Then slowly go back up to speed with the engines in mid position.

The Tom Cat handles following seas well; sometimes an adjustment of the angle of attach is necessary, but we have not had any problems in similar conditions.
 
Thanks for the insights everyone. I don't think the issue is a thermostat because I replaced both of them in May. One thing I was confused about when the incident happened was that both engines were rev limited. I assumed that both were over heating (and maybe they were) but when I read the manual it stated that if one engine overhears both will be rev limited. I assume that this occurs to keep rpms about the same on both engines.

In the meantime I'm going to assume that I over trimmed and that caused at least one engine to overheat. Lesson learned.
 
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