Temp gage

Jan 27, 2008
3,045
ODay 35 Beaufort, NC
I posted this on the ask all sailors forum but am copying it here for you guys with the same boats.

I've recently upgraded my heat exchanger in my Universal M25 engine to the recommended 3" diameter. I also just installed a new exhaust riser and water injection pipe. After powering for about 12 miles on Friday in zero wind my temperature gage was rock steady at 160 degrees (the thermostat setting on the M25).

Leaving the anchorage on Saturday motor was running fine and we were creeping along avoiding other boats and I looked at the temperature gage and it was pinned on the max side of the gage. Needless to say I almost had a heart attack, as we were in close proximity to other boats and entering the channel to leave the anchorage. The engine showed no signs of overheating, meaning no steam in the exhaust, no black or gray smoke, I felt the coolant cap and it wasn't hot so I opened it and there was no sign the coolant was anything other than normal. I had excellent cooling water flow out the exhaust. We powered at low speed to the end of the channel and I hoisted a jib and killed the motor. For the next ten miles the gage stayed pinned at the max. When I turned on the key periodically to power the gage it would tend to move toward the high side but never indicated the engine was cooling down. Entering our inlet I started it (the engine) up and it started fine and ran fine back to our slip, about another 2 miles. The gage just stays pinned at the max.

So my question to the experts here, is the gage fried? Do I need a new temp sender? I read in the archives a temp gage is like an ohm meter, could it just be a bad connection somewhere causing extreme resistance driving the gage to infinity? I see in West I can get a gage and sender for about 50 bucks but will need to see if the sizes will match. As additional information, the gage has had some condensation in it for a while, while running there is some mist on the inside lens of the gage that disappears when not running, so I know the gage is not hermetically sealed.

Any thoughts on this conundrum?
 
Mar 11, 2015
357
Hunter 33.5 Tacoma, WA
As I said earlier, get a laser temp probe to measure the REAL temperature (point it at thermostat housing). Right now you are just guessing. Yes, you most likely have a bad connection (heat induced).
 
Jan 27, 2008
3,045
ODay 35 Beaufort, NC
I updated troubleshooting info on the ask all sailors post. The laser IR probe is an excellent idea. I'll pick one up ASAP.