Strange Temp Issue

[stinger222]

Fresh 489 engine with 10 hrs been running great since last Fall, dead on 160 deg, but running about 30 mph yesterday, noticed temp gauge no longer registering anything. Come down off plane, noticed risers still cool to the touch. Drive 7 mi back to marina, shut off engine, ground sender wire, key back on, gauge pegs, so I figure bad sender. However when I hook wire back to sender, gauge then works, registering 210 deg. Top end of engine feels hot. Start engine, temp gauge goes back to 120. Replace sender, same behavior. Temp registers around 210 but only when stopped in the slip with key on, no reading when engine running.

Removed thermostat, tested it in pot at home, opened up perfect at 160.

Raw water impeller new in Feb, water circ pump new in Feb also. Have been hanging out at this sandbar that I have never been to for the last 5 weekends. Pulled hose off at oil cooler, n restrictions, no mud that I could see. pulled petcocks from block, clean water drained out, no sand. I 'm stumped.

 

[Grub54891]

Re: Strange Temp Issue

Bad sender wire connection? Check em all,even under the dash.
Grub

 

[stinger222]

Re: Strange Temp Issue

replaced the gauge, same result, replaced wire from sender to gauge and replaced thermostat with a new 143 deg thermostat, still same behavior. Replaced thermo housing gasket with the correct gasket with brass rivets. Replaced sending unit. Same result. However the new quicksilver sending unit came with some red sealant on the threads. Should I have removed it? Why would they put thread sealer on there and risk messing up the ground connection.