Johnson 1995 100 hp overheat alarm

My boat has been in storage for the past year while I was activated to military service. I recently returned home and got the boat out of storage. The Johnson 1995 100 HP is a V-4 with VRO system and it has a V-6 lower unit. It is a commerical 100. Anyway, the overheat alarm has tripped off after about 3 minutes of less than 2000 RPM. It has never done that before. The boat was stored in an area where the weather was below freezing on occasion. I thought I flushed all the sea water out. Prior to the engine check, the water pump was examined and it was functional. The alarm went off when I did a engine check while on the trailer. The eninge was "spitting" just fine. Would the thermostat be bad or is it one of the heat sensors? I did not see any water leaking from the power head. I did not see any loose, broken, or frayed wires so shorts may be out. Any ideas?

Re: Johnson 1995 100 hp overheat alarm

Welcome to iboats.

If in fact it is NOT overheating, you may need to test the heat sensors as per your manual.

If it is overheating, may be the water pump/impeller, t stats sticking closed, or a restriction in the cooling circuit.

BTW, thanks for your service overseas

Re: Johnson 1995 100 hp overheat alarm

Chris,

Thanks for the advice. I disassembled the t-stat housing and pulled them. They were corroded and stuck open. I also found quite a bit of calcium carbonate buildup inside the hoses and into the power heads. I've ordered new t-stats, gaskets, and will attempt to make the full repair and test within the next month. So much to do, so little time. Anyway, I'll let you know how it turned out.

Re: Johnson 1995 100 hp overheat alarm

Chris,

I finally was able to install the new t-stats and gets some fresh gas through the motor. The engine started just fine and after 10 minutes the over-heat alarm went off again. I did not shut off the motor but let it keep running. I checked for leaks, water pump injection (spitting at orifice), and the new t-stat housing & install. I also checked the sensor wiring and made sure all the connections were good. After about 15 seconds the alarm went off and the engine ran just fine. I think there was significant calcium carbonate buildup on the sensor and the long term storage may have corrupted the sensors. Fresh sea water in the cooling system may have solved the problem. The end result is the engine was idling great, the temp was normal, and no alarms.