Temp gauge on 3YM20 inoperative (B-1 panel)

SFS

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Aug 18, 2015
2,066
Currently Boatless Okinawa
My temp gauge stopped working (stuck on coldest temp, far left side of the gauge) a few days ago. On the day after it stopped, it did show a rise in temperature once during the day, but never a steady temperature. Instead, it was a "jittery" readout, with the needle shaking quite a bit.

I have pulled out the service manual, verified the wire involved, and find no issues with the connections at the engine end. Since 90% of electrical issues are connections, I plan to open up the instrument panel tomorrow and check those connections.

1) Does anyone have any ideas on other things to check?
2) Any pitfalls to avoid when opening up the panel?
 
May 24, 2004
7,129
CC 30 South Florida
The pin connectors for the harness wiring from engine to control panel are usually the culprits. The harness wiring itself can also chafe usually as it gets routed around sharp fiberglass corners. Check voltage and continuity for the connectors and a visual inspection of the harness insulation specially around bends.
 
May 12, 2004
1,502
Hunter Cherubini 30 New Port Richey
I also have the 3YM20 Yanmar that came with the B-1 panel but my panel only has idiot lights. Did yours' come with the gauges or were they added?
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
@SFS think it is a sign of Global Warming. The Gulf stream has finally changed. Look out for icebergs.
 

SFS

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Aug 18, 2015
2,066
Currently Boatless Okinawa
I also have the 3YM20 Yanmar that came with the B-1 panel but my panel only has idiot lights. Did yours' come with the gauges or were they added?
The PO put this engine in, and she wasn't the kind to spend more than the minimum. That being said, it has the optional 80A alternator, rather than the standard 60A, and it has the temp gauge. No oil pressure gauge, so I suspect the temp gauge was left over from the previous engine, and the mechanic used it again.
 

SFS

.
Aug 18, 2015
2,066
Currently Boatless Okinawa
I didn't find any issues with connectors, or connections with the panel out. Everything was tight, no corrosion anywhere. I didn't spend a ton of time troubleshooting with my voltmeter. I'll have to dig more deeply another day.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Know you have a Hunter. Can not find what Hunter has done with their install. The Catalina folk go into the difference between a "Yanmar and a Catalina Yanmar" install.
This custom made temperature sender is used exclusively in Yanmar Diesel engines aboard boats built by Catalina Yachts. The standard Yanmar engine uses a sender with nonstandard threads and an impedance matched to European instruments. In order to use American instruments aboard your Catalina, the engine distributors had to replace the standard temperature senders with this custom sender before the engine was shipped to Catalina Yachts.

These replacement senders are machined to fit Yanmar's metric threads and the impedance matches that of our #Z2650 temperature gauge shown below with a maximum reading of 240 degrees. The original senders can be identified by the green seal that surrounds the electrical connection on the sender, shown below in "More Images:." Current senders have a black seal as shown above.

Important notes:
1) Unless they are intimately familiar with Yanmar engines installed on Catalinas, it is highly unlikely anyone will be aware of this custom part. Speak to any normal Yanmar parts source either at a boat yard or any of Yanmar's many distributors across the country and it is likely you will receive incorrect information due to the specialized nature of this information.

2) It is rumored that at some point (reportedly in 2000 and 2001 but the exact years are questionable) the employee responsible for preparing the engines before forwarding them on to Catalina Yachts ran out of these custom senders. The engines were shipped to Catalina with Yanmar's standard senders installed without anyone knowing it. This might explain why some owners report problems with their temperature gauges on Yanmar equipped boats.

Check the color of the seal surrounding the center electrode. If it is green it is likely (but not guaranteed to be) correct. If it is other than green and you are having issues with your temperature gauge and have ruled out the wiring and gauge itself, then you should replace the sender. Current senders are supplied with a black seal.​
You are going to need to check threads is you are going to replace the sender. You will want to have the sender match the gauge to get the proper resistance - temp report on the gauge.

SBO has some sensors. Cost appear to be about $16. The Special Catalina sensor cost is about $36 direct.
 
Jun 11, 2011
1,243
Hunter 41 Lewes
I'm pretty sure if you put an alligator clipped wire on that sending stud and the other end to ground the gauge should pin to hot. If it does the sender is bad, if you have the panel open and you can read continuity to ground with the alligator clip on then the wire is good and most likely the gauge is bad.
 

SFS

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Aug 18, 2015
2,066
Currently Boatless Okinawa
Well, I found the problem, admittedly by accident, and while working on something else. While inspecting the impeller, I looked up and saw a wire terminal askew on a stud, and the nut backed off A LOT. Tightened it down, looked at the wires involved, and went, yep, that's the circuit. Sure enough, gauge works fine today.
 
Oct 22, 2014
20,995
CAL 35 Cruiser #21 moored EVERETT WA
Oh wow. The theory works. It’s a miracle.
The problem is identified and solved the last place you look.
I love it.
Congratulations @SFS for your success.
 

SFS

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Aug 18, 2015
2,066
Currently Boatless Okinawa
Thanks John. I knew it had to be a connection, as I stated in the OP. I just (unknowingly) hadn't traced ALL of the wiring to ALL of the components. DOH!
 
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