Erratic Temperature Gauge

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Oct 15, 2007
Vessel Make
Ocean Alexander 38'
Our*starboard temp. gauges (both upper and lower) *have been problematic ovet the last 2 years.* Once the engine reaches operating temp., around 185-190, the guage will register there for a short time and them steadily climb all the way past 220, where it will stay until we shut it down.* Using a infared temp. tester, we determined the engine was not actually overheating.* I replaced the temp. sending unit and same problem.* I also switched the leads from starboard to port and got normal reading on the port gauges.* Any suggestions on how I can test the starboard gauge to determine if it is faulty?* Possibly a short?* Anyone else ever have this issue?
>"Any suggestions on how I can test the starboard gauge to determine if it is faulty? "

It sounds like you just did. If you fed the signal from the starboard sensor to the port gauge and got a normal reading then it would seem to me that the starboard gauge is faulty. I don't know what kind of gauges your boat is fitted with but most boats, particularly older ones, have pretty inexpensive gauges. If they go south it's generally not worth trying to fix them---- it's much easier to simply replace them.

I have not had the problem you describe with our boat, but I have with a vehicle. If the temperature exceeds a certain amount, as when going up a grade, the temp gauge will sometimes climb to its maximum reading.* A whack on the gauge brings it back down to the proper reading.* In this case (a 1973 Land Rover), the problem is apparently an iffy instrument voltage stabilizer. In the Land Rover, this is a separate little component that's mounted to one of the instruments in the panel. I have no idea if boat instruments use a separate voltage stabilizer for the instruments, if each instrument has its own stabilizer built-in, or if voltage stabilizers are even used at all.

In any case, since none of your other instruments seem to be affected, I would think replacement or your one bad gauge would be your best solution.

-- Edited by Marin at 15:06, 2007-12-26
Hmmm.. electrical in a 1973 Land Rover.

Sounds like Lucas - Prince of Darkness...
I have owned two British vehicles since new--- the 1973 Land Rover and a 1991 Range Rover. Other than the intermittent instrument voltage stabilizer problem, I have had zero problems with the electrical system in the Land Rover in the last 34 years. The only electrical components in the Range Rover that have given any trouble so far were made in Germany by Siemens. Go figure......
Just a shot in the dark on this, but in my experience a short is a quick one time abnormal movement. A bad ground is the slow moving, dim light, sometimes it does it sometimes it doesn't problem.

If it were me I'd loosen the mounting nuts on the guage, wiggle it around a little to scrape a clean surface, then retighten and see if that makes it all better. Changing the wires to the other guage and it then working properly tells you the problem is the particular guage. Working OK sometimes and not others says there is a variable in the mix.

Do you notice that it goes off scale when the cabin gets warmed up? That could be the guage expanding a little and losing it's only little spot that it is grounding in. Could it be that it acts up only after you turn on another item? Are they grounded together causing the problem?

Guages that act up only when warm can be "simulated" with a hair dryer to warm them up and cause the fault without running for 1/2 hour or whatever. Just let the engine run in the slip, in gear will bring the temp up faster, but in either case use the hairdryer to heat up the guage and see if you can't make it peg even before the engine is warm.

Ken Buck
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