Johnson 75 cooling water

[ericulvila]

First post from new user; Eric

I was beginning to see what looked like temperature creep based on my gauge. Gauge has no actual temperature readings. Just a dummy gauge with cold to hot scale. Motor has been running great for the last three seasons. Its a 1981 Johnson 75 HP with low hours used in saltwater.

I replaced the pump and the thermostat and I checked the relief valves. Everything looked good and no sign of corrosion inside thermostat housing After testing the new pump the gauge shot right up to about half way. I started to suspect that something may have changed in the gage or sender, (resistance possibly). Normal readings on the gauge were usually only about 1/8 off the low point.

I verified that the cylinder head temps were around 125 to 135 at idle using temp gun. Water is coming out the tell tale, the front of the lower unit and the six holes above the gear case. There is also water coming out little hole on the lower unit and no water out the propeller hub. Does any of this sound unusual? Do gauges and senders go bad giving a false reading? Does anyone recommend pulling the head or head cover for further inspection. I have never had the high temp horn go off.

 

[johnnygjr]

check the middle housing for excessive temperature.

 

[ericulvila]

do you mean the cylinder wall?

 

[johnnygjr]

no,exterior of motor,midshaft housing area. where exhaust runs through!

 

[ericulvila]

what is excessive temp readings there? what would temp would you expect there? I replaced the water pump recently and found the exhaust seal gasket on the lower unit partially melted, not to bad.

 

[johnnygjr]

Check wiring for loose, corroded connections at gauge& sender,clean them up.check your wiring disconnected with an ohm meter from sender to gauge. try another gauge.