1990 Johnson 70hp J70TLESB temperature sensor (switch) good/bad?

[Lakemichfish]

I checked the temperature switch (or sensor) on my 1990 Johnson 70hp by putting it in a pot of water. It was activated at 208F. This seems way too high. What temperature should it be triggered/activated at?

 

[flyingscott]

I believe that is correct.

 

[racerone]

Book says 203 +/- 6 degrees.----So why you say " seems way to high " here ??

 

[Lakemichfish]

It seems really close to boiling and much higher than operating temperature.

I moved the telltale hose to the top of the exhaust manifold. I have a good thermostat, impeller, water pressure (25psi), temp sensor but the overheat alarm still goes off after 1-2 minutes of running at 3000 rpm after a 2 mile WOT run.

 

[flyingscott]

Is the VRO still hooked up?

 

[Lakemichfish]

No, VRO is disconnected.

 

[oldboat1]

Is the motor that hot on top of the cylinder head? Wouldn't be able to touch it at that temp, but good idea to get the surface temp with an infrared tester.

 

[racerone]

He said he tested this switch in boiling water.----No damage will occur at 208 degrees F.----After all many automotive engines run with a cooling system that is pressure controlled.----Raising the pressure ( 12 PSI ) also raises the boiling point up to around 240 degrees F

 

[oldboat1]

But the whole point of a temperature sensor is to sense elevated engine temp. Start by determining engine temp by another method, then decide whether the sensor mechanism is doing its job.