I have a pair of 1988 Merc 135 outboards on 23' CC. Last summer, a couple trips after water pump impeller changes, I noticed that the starboard engine was showing higher temps than normal at mid range rpms(1000 to 2500rpm)- the port remained normal.<br /><br />I shut the engine down and let the other one push us home. The next day I fired them both up and found that at idle the starboard ran cool. At the mid range it showed hot but if I got up on plane at higher revs it cooled back down and showed normal.<br /><br />When the starboard engine shows high temps, I occasionally stop to check the pee hole water and find it 'touchable' - probably 110 or so - certainly not the high end temps being indicated and only very slightly warmer than its twin.<br /><br />As far as I can tell the temp sending units are small cylinder shaped items slightly smaller than a dime in diameter and about 1/2" tall. they appear to lightly touch the valve cover. The stamped detail on these items reads: 438106 33/03 12 volt. I can find no other senders. <br /><br />I'm reasonably confident that the overheating is not real but the false reading are driving me crazy. Can anyone help?
