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Fleet Admiral
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- May 26, 2009
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I think I know the answer but thought I'd throw it out there:
this weekend my boat suddenly sounded the heat alarm; we stopped immediately. it would sound when you turned the key without starting; this continued about 5-10 minutes after the first time. Towed it to the house.
It just had a new water pump installed so that was a suspicion, but it pumped fine, ran at idle no problem (later). I removed the thermostat and water pumped out that hole; I replaced the thermostat anyway as it is at least several years old in high salt water.
after replacing the thermostat and having no issues at idle, I creek tested it. ran fine for a 5 minute run at about 3/4 speed (on a plane) but sounded off after a minute or so at high speed. Turns out the first time it did it was when my daughter, who was driving, ran it up to high speed. And before her incident I ran it about 3/4 speed for a 5 minute test run, no issues.
The next day I ran it about 20 minutes at mid speed, but on a plane, no issues (rather than tow from the house to the ramp I ran it with a second boat following to tow).
Like many coastal boaters I don't run WOT much and have a comfortable cruising speed with a "sweet spot" on the motor; however high speed isn't really screaming like an over-revved motor. No tach, not sure of the prop pitch but it's supposedly matched with the motor. No oil alarm. When the alarm went off it wailed and I shut down immediately but did not feel that "slowing down" that occurs with a bad overheat (BTDT).
Suggestions are to get a heat gun and see if it really is overheating or if the alarm is over-sensitive. Or maybe I should hook up the tach and see what's happening.
BTW the boat is left out of town and I am home so I can't go check it until next time I go there.
Johnson 70 from about 1987, run hard in salt water when used but only used about 8 x a year and mostly for short (20 minute) runs for transportation to an island and around the marsh. A beater motor on a beater boat.
My conclusion is that the higher RPM's are too high and causing it to approach overheat level. Solution is to reinstall and watch the tach, adjust the prop to keep within limits, test the alarm's sensitivity with a heat gun. Can you put a governor on an OB like that?
thanks in advance for your expertise!
this weekend my boat suddenly sounded the heat alarm; we stopped immediately. it would sound when you turned the key without starting; this continued about 5-10 minutes after the first time. Towed it to the house.
It just had a new water pump installed so that was a suspicion, but it pumped fine, ran at idle no problem (later). I removed the thermostat and water pumped out that hole; I replaced the thermostat anyway as it is at least several years old in high salt water.
after replacing the thermostat and having no issues at idle, I creek tested it. ran fine for a 5 minute run at about 3/4 speed (on a plane) but sounded off after a minute or so at high speed. Turns out the first time it did it was when my daughter, who was driving, ran it up to high speed. And before her incident I ran it about 3/4 speed for a 5 minute test run, no issues.
The next day I ran it about 20 minutes at mid speed, but on a plane, no issues (rather than tow from the house to the ramp I ran it with a second boat following to tow).
Like many coastal boaters I don't run WOT much and have a comfortable cruising speed with a "sweet spot" on the motor; however high speed isn't really screaming like an over-revved motor. No tach, not sure of the prop pitch but it's supposedly matched with the motor. No oil alarm. When the alarm went off it wailed and I shut down immediately but did not feel that "slowing down" that occurs with a bad overheat (BTDT).
Suggestions are to get a heat gun and see if it really is overheating or if the alarm is over-sensitive. Or maybe I should hook up the tach and see what's happening.
BTW the boat is left out of town and I am home so I can't go check it until next time I go there.
Johnson 70 from about 1987, run hard in salt water when used but only used about 8 x a year and mostly for short (20 minute) runs for transportation to an island and around the marsh. A beater motor on a beater boat.
My conclusion is that the higher RPM's are too high and causing it to approach overheat level. Solution is to reinstall and watch the tach, adjust the prop to keep within limits, test the alarm's sensitivity with a heat gun. Can you put a governor on an OB like that?
thanks in advance for your expertise!
