Mariner 30HP 4S - Overheating

[tobybudd]

Hi all,

I have an oldish 30HP Mariner four stroke, year unknown.

Had an overheating problem, replaced thermostat and tested it using a multimeter on the temp sensor and confirmed it is opening at the correct temp. But it is still overheating.

Remove thermostat and run engine and no overheating.

Tel tale is running clear when engine runs.

Thoughts appreciated.

Toby

 

[Texasmark]

Possibly a bad stat out of the box. Bottom of the pellet the same temp stamped as your old one? 30 hp surely doesn't have/need a high flow popoff valve so engine block flow is only limited by the stat and it's flow path. You tested the flow path by the fact that no stat and no alarm so it must be open.

Carefully insert a string between the moving parts and put it on the stove in a pot of water with a candy thermometer (has enough heat range to detect temp required). Heat the water while holding the stat off the bottom of the pot with the string and monitoring the thermometer. Stat should fall free within 10% of the number stamped on the bottom of the pellet.