Thermostat Issue with 2005 90 Hp Johnson

[leadhead]

my 2005 Johnson 90 HP outboard (J90PLSO) over heat alarm went off at the begining of a fishing trip about 2 weeks ago --- I pulled the thermostats and fished the rest of the day without them without a problem --- then ordered two new BRP Part # 435491 thermostats to replace them --- installed the thermostats and had the very same issue on the next trip --- I again pulled the thermostats and continued my trip --- the next day I placed the new thermostats in a water filled glass pot I have along with an old thermostat that still works --- I heated the water slowly to a temp of about 170 F --- both of the new thermostats did not open until temps in the pot of water exceeded 155 F --- the old thermostat started to open at about 100 F to 110 F and was fully open at about 135 F --- when the new thermostats did open they only opened about half as much as the old thermostat --- I'm not positive but I believe this motor is supposed to run at around 140 F --- the water pump is not new but is only 2 seasons old and I almost never wear them out ---I usually replace the pump every 5 years while they are still working --- I'm always in deep (salt) water and never suck sand or other bottom materials up into the lower unit --- the motor is always flushed with fresh water at the end of the day or the very next day --- looks like the new thermostats are bad to me but thats why I'm posting --- any ideas ? ? ?

[boats.net]

The thermostats are suppose to start opening at 143 F and fully open at 170 F. You should change your water pump impeller every 2-3 years, but sound like your impeller is not supplying enough water to the engine (I recommend replacing).

[leadhead]

Hi Boat.net

Thanks for your response ! ! !

I can change impeller but why don't the new thermostats open at a lower temp like older thermostat around 100 F 110 F --- my service guy says motor should run at 140 F --- it will run hotter then 140 F if the thermostats don't even start to open until 155 F and do not open as much as the older one even at 170 F

Thanks for your time
leadhead

[boats.net]

I cannot answer why the old thermostats open so early, could have a week spring. The service manual is where I got the information.