Merc 470 temperature gauge

[Ppichey]

Hello,I have a 1980 mercruiser 470 and as soon as I turn the key on my temperature gauge pegs out at 240 with the engine being stone cold.any idea what could be causing this?thanks

 

[Bondo]

Ayuh,..... Welcome Aboard,...... My Guess is, either the sender is goin' to ground, or the wire 'tween the gauge, 'n sender is grounded out,.....

Disconnect the sender, 'n see what the gauge does,.....