1999 F100 Alarm - overheating

rmkjr

Recruit
Joined
Aug 19, 2006
Messages
1
Last season an alarm went off a couple of times. Neither the oil or temp indicator lit up. It would run OK after stopping the engine and immediately restarting it. This year the alarm is sounding more frequently and the telltale stream was very warm/hot. This symptom has progressed to where the telltale stops. Stopping the engine for a few minutes and restarting it would solve the problem some of the time. So, I checked the impeller - it is in great shape. I removed the thermostat and found a minute amount of algae/moss and cleaned it up. I removed the pressure control valve and found a minute amount of algae/moss and cleaned it up. Ran water through the flushing fitting for ten minutes. Got back on the water and NO telltale and the alarm sounds after three to four minutes. Stopping the engine and immediately restarting it stops the alarm but the telltale is still not present and seems to emit a little steam. I'm out of ideas. HELP!
 

rodbolt

Supreme Mariner
Joined
Sep 1, 2003
Messages
20,066
Re: 1999 F100 Alarm - overheating

do a leakdown test, that will locate any headgasket failures caused by an overheat.
if a leakdown passes replace the waterpump kit,clean the pressure valve pocket and install a new grommet and replace the t-stat.
also grab an 06 yamaha marine tech guide so you can properly test the alarm system. you will need a 220 Ohm 1/2 watt resistor to test the overheat alarm system.
if its overheat or oil pressure it should go into RPM reduction and give the proper indicator lamp, if the factory tach is used and properly set up.
 
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