No Telltale at Higher RPMs

[Sogden74]

I have a Mercury 2006 30hp 4 stroke that had an overheat alarm. The telltale runs strong at idle but quickly stops at higher rpms. New waterpump kits all OEM, which didn't help. Telltale starts almost immediately when dropped back to idle.

This condition has been repeatable on the lake and in water trough. Fresh water only motor. Don't know of this may be a clue to the problem but the telltale doesn't seem stop when up the idle speed when prop not engaged.

Other than this it starts excellent and runs like a sewing machine.

 

[Texasmark]

I don't have a 4 stroke. On my 2 stroke of that year area, larger engine I have a thermostat that controls block temp up to about 2500 RPMs and a larger diameter pop-off valve that unseats and allows uncontrolled water to bypass the stat and allow for larger volume. If you have such and the pop-off is stuck shut you will have your problem.....I did on mine after I bought it used and during the first outing. On the 2 stroke, the valves are under a scabbed on cover on the top rear of the rear water jacket cover which encircles the spark plugs.