late 80's early 90s 40 yamaha overheating alarm issue

[ctkiteboarding]

ok , my 40 Yamaha got hot this spring so i did the basic stuff impeller and thermostats

now the engine runs for a while and after i run it wot for a few minutes the motor bogs and then kicks back on then bogs,, the alarm light sometimes goes on and sometimes it just bogs,

its not super hot , i can hold my hand on the block for a minute or so,,,

then it will start to run fine for a few minutes , then bog ,bog and the lite goes on for second ,then off and it runs great again,,,

it does not get the boggin and alarm issue when at slow speeds,,,,

can the overheat sensor be screwed up and shut the motor down??

 

[Ray Neudecker]

Re: late 80's early 90s 40 yamaha overheating alarm issue

The sensor can be tested by placing in a pan of boiling water. the sensor should have a resistance of 3.0kto 3.4 k at 212 degrees and 128k at 40 degrees. You may need to pull the head to see if corrosion has blocked a passage or the gasket is leaking.