I have a Westerbeke
on a 42' sailboat. Last weekend, about 30 minutes after leaving the mooring
, I noticed the temp gauge was reading about 230 (but not pegged). We usually run at 190 on the gauge. The audible high temp alarm
had not sounded (it's supposed to sound an alarm
I shut down the engine
, checked the strainer (which was clear), checked the coolant
level (fine). I started the engine
and confirmed that the usual amount of cooling water
was being pumped out of the exhaust
Shut it down again, and sailed most of the way back to the mooring
. The last bit is a narrow channel with the wind
on the nose, so we started the engine and idled back in. The temp gauge started about 150 (the engine had cooled while we were sailing), but climbed back up above 220.
Once back at the mooring, we checked the gauge (shorted the S pin to ground, it pegged to the right; disconnected S, pegged to the left). It seems the gauge has not failed catastrophically, if it has failed.
Next, I removed the wire from the temp alarm switch and shorted it to ground, and the alarm sounded properly. Of course this doesn't prove that the switch is OK, but it eliminates the alarm buzzer.
Next, I disconnected the gauge at the temp sender on the engine and started the engine, and measured the resistance to ground as the engine warmed up (at 1000 rpm
or so in neutral, not loaded). I took temperature measurements on the engine using a laser infrared thermometer, at the block next to the temp sender and at the thermostat cover. As expected, the temp vs. resistance curve was a nice logarithmic curve. The temp readings never went over 177, even after 20 minutes or so (when it leveled off). The highest temp I could find on the engine was the oil
pan, which was 188 (by the way, all of this argues for taking these readings on your engine before something goes wrong, so you have a baseline!).
Here are my conclusions, and I'm hoping for confirmation or an explanation of why I'm wrong:
1. The engine isn't overheating
. The block next to the temp sender was 175 degrees. The alarm didn't go off. Plenty of coolant
, and plenty of sea water
2. The gauge or the sender is bad. I wish I had more confidence about this. My thought is that when either of these fail, they fail completely. I haven't been able to find an exact temp vs. resistance curve for my sender. The only one that I found was similar to my curve, but shifted (it had a lower temp for same resistance). My plan is to replace the sender as a first step.
Could it be something completely different, like a thermostat problem or an air bubble somewhere?
The engine has been working fine all season, and I haven't done anything to it that would have caused this. Two years ago I had the heat exchanger
off and flushed the cooling
system, so I would think that any air bubbles would have worked their way through the system by now.
Any ideas are much appreciated. Also, when I replace the sender, do I have to worry about air getting into the system?