2000 Johnson 150 HP overheat alarm

I have a Johnson 150 HP. While going out last week, the overheat alarm came on. I went to the back and looked at the stream coming out of the motor, it appeared the water pump was running just fine. <br /><br />Thing is, I was idling through a no wake zone when this first happened. I turned the motor off and immediately back on and the warning went away. About 10 minutes later, it came on again. This time, turning it off then on didn't fix it, so I waited about 2 minutes, and it ran again at full speed for about another 40 minutes before the alarm came on again.<br /><br />It does not appear to be overheating. Any ideas what could be causing this, or whether or not it really is overheating? I believe it's not overheating, because I don't think 2 minutes of downtime is enough to dissipate the heat from a motor.

Re: 2000 Johnson 150 HP overheat alarm

I did the same thing once in a really merky lake. The alarm came on and even though the tell tale hose still weeped water I found that the water intake was a little plugged with sludge. I cleand it and no more problem. Remember, the tell tale hole doesn't really represent the water pressure in the engine and in fact, the amount of water discharged won't change much when the pressure is low. As far as two minutes cooling down... sure. There may not be a lot of historesis on the thermostat. It sort of makes sense that the thing would not alarm for the 40 minutes at full speed because it was drawing more water than when at idle, just not enough to keep the engine cool when used harder. I would trust the alarm and take a look at the condition of the impeller. Some people recomend changing it once a year if the motor is used heavily or often in sandy water. I replace mine every two years; they're inexpensive.

Re: 2000 Johnson 150 HP overheat alarm

Yeah, the impeller was my first thought. I will replace that next week. Since you mention murky and sandy water, I remember it DID land in some unseen sand bars about 2 weeks ago...I blackflushed the cooling system and ran it with the muffs and had no problems until the next time I went out. It only overheated once then...and I was out for over a tank of gas...all day. Could the sand have made its way into the cooling line and eaten my pump?

Re: 2000 Johnson 150 HP overheat alarm

Sure... sand can be rough on the impeller. When you take the thing apart inspect the pump housing closely for wear. Replace the housing if you have to. You can buy the impeller 3 ways... alone, with gasket and o-rings, and with the housing.

Re: 2000 Johnson 150 HP overheat alarm

thanks, I think I'll be safe and go with the one with the housing and give it a try...probably should change the thermostats too.

Re: 2000 Johnson 150 HP overheat alarm

Make sure that you really get all of the sand out (can be tricky).<br />Had to flush mine several times and also did put the stats out cause i found some sand stuck there to, flush it with the stats out to be sure.