Erratic temperature gauge

[HerbertFriedman]

While motoring for about 30 mins with the temperature stable at 140 deg, suddenly the temperature gauge shot up to 200 degrees and then bounced quickly and erratically between 200 and 220 (pegged). I shut down the engine immediately and sailed for about 10 mins, then restated the engine. It ran perfectly at low rpm for another 30 mins until I got to the dock. Water was flowing out of the exhaust (raw water cooled engine).

I did not want to rev up the engine until I checked it out. I checked the connection on the temp sender and inspected the impeller, all OK. Maybe some junk covering the intake port? Does not feel like normal overheating since this was not gradual but very sudden and sharp movements of the temp gauge. Any thoughts?

[Kelly]

Just a thought: I think you're right when you say that this does not sound like "normal" overheating. I don't think you would see the temperature "suddenly shoot-up" as overheating does take some time (minutes). And "bouncing erratically" sounds more like an electrical problem than a temperature problem.

Problem with the gauge? With the sender? With the wiring?

Seeing normal flow from the exhaust is a very good sign:)

Kelly

[tenders]

This happened to me a few years ago. I never figured out why, but it sure freaked me out, especially since I run without a thermostat and have blocked off the bypass and the engine normally runs quite cold. I did an acid flush and installed a high temperature alarm. It hasn't happened since and with the alarm I don't worry about it.

[HerbertFriedman]

I ran the engine this weekend at the dock for 30 mins at mid throttle, no problem. My erratic temperature guage may have been caused by some junk getting sucked against the cooling water intake.