[C320-list] Engine water temp problem

[Graeme Clark]

First time I run the engine this year the water temp gauge goes off the clock!
I therefore bought a point and shoot laser thermometer and sure enough the engine temp ( measured where the sensor is and also at fuel injector points) is around 170f whereas gauge is showing 280-290f

So it's the sensor or the gauge. How do I test the sensor. There is only a single terminal so I'm guessing the resistance changes with temp. Does anyone know what resistance should be at say, 170f ?

Or is there a simple way to test gauge

I did have the instrument panel out this winter to repair the lid so it could be a dodgy connection I guess. I'll check everything again but any more info would be handy as I'm stuck on boat with limited internet access!

Graeme
#366, 1996 running Yanmar 3GM30F


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[Allan S Field]

Our boat was about 10 years old when the temp sender unit failed. A
replacement was ordered from Yanmar for about $20 US 7 years ago and
installed in about 10 minutes. Problem fixed.

Allan S. Field
Sea Shadow - C387, #103
Columbia, MD

[Jeff Hare]

Allan, you might want to check whether you actually got it from Yanmar or
from Seaward...

The standard Yanmar one for the 3GM30F engine isn't (typically) compatible
with the Catalina engine instrument pod's temp gauge. The stock yanmar
sender unit is typically compatible with the stock yanmar engine panel's
temp gauge. The one on Catalina yachts is typically a Stuart Warner unit
with a max temp of 240 degrees. The resistance range is 240ohms -> 33ohms.

Catalina Direct carries it as does Doug Igarashi (diga...@earthlink.net)
who as far as I know still sells the original Seaward line of products. I
rather suspect CD gets them from Doug...

Worth looking into before running down to your local yanmar dealer (who will
almost certainly sell you the wrong part).

-Jeff Hare

[Allan S Field]

Ouch! You are right - it came from Seaward.

[Graeme Clark]

Jeff
Am I right in assuming the resistance decreases with temperature it is it the other way round
Immediately after I shit down the engine the resistance across the sender was about 35 ohms. The gauge was off the high end of the scale at that point!
Graeme

Sent from mobile: please excuse typos etc.!

[Jeff Hare]

Yup, you're excused. Autocorrect is hilarious. 😊 Anyway, sounds like bad sender. You can pretty easily check it using the procedure on our website.

http://c320.org/article.php/2012072022490543

-Jeff

[Onat Dogruer]

On a side note, I just replaced the 18 year-old Johnson water pump (with same model Johnson pump) on our Yanmar and the temperature is not going above 160. It used to hover around 170F. I wonder if they improved somehow the efficiency.
-OnatKittiwake #546, 1998

[Rick Sulewski]

Graeme,
If you did anything with your wiring over layup you could have a sensor lead grounding and pegging your gauge. For example, several years ago I had my valve cover off to adjust my Westerbeke valves and inadvertently pinched the temp sensor lead when the cover was reinstalled and that caused my temp gauge to peg.
Rick

[Graeme Clark]

Rick
Thanks for the tip but the gauge does "climb" as the engine warms? it doesn't go straight to max reading!
I haven't yet had a chance to troubleshoot further. Possibly tomorrow if it's fine weather as I want to start by cleaning up all contacts.
My gut feeling is the most likely reason for a problem is because of something I did rather than a random failure whilst the boat was laid up over winter - it would be odd for a temp sender to fail when it sits in an unused engine for six months, surely!
All options will be explored though!
Graeme

Sent from mobile: please excuse typos etc.!

[Jon Vez]

Graham,
An easy way to test if the sender is good is to put it in a pot of water with thermometer and bring the pot to 170-180F and you can see it pop open if it's good.....

Sent from my iPad

[Jeff Hare]

Wouldn't that be the test procedure for the thermostat? I suppose you could
test the sender that way also, as the water heats, you should see the
resistance on the sender drop as well.

[Jon Vez]

Sorry, yes I was referring to the thermostat....

Sent from my iPad

[Rick Sulewski]

Graeme,
I recall that some aging antifreeze over time could tilt toward becoming
acidic and even attack certain metals, seals or gaskets and that activity
could introduce some gunk into the engine cooling system and increase engine
temps. Given the small cost of a sender, I replaced mine before I discovered
that I had pinched the lead and that was causing the gauge to peg. The new
sender began to read an even lower temp once I discovered the cause of my
gauge pegging.
To reduce cooling system issues I try to replace/refresh a portion of the
antifreeze every three years.

[Graeme Clark]

Nothing wrong with gauge
Nothing wrong with sender
I bought a new terminal connector block, cut back all the wires 1/4 inch and bared new copper and remade all the connections (finishing by applying a conductive non soluble gel [contralube 779] to protect from future corrosion)
I also cleaned and remade several connections to instrument terminals
All now working fine - boat electrics remind me of old VW cars - it's usually a corroded contact!
I also took the opportunity to fit a new ignition switch that has an Accessory position as well as an ON position. To the ACC terminal I wired the blower, so now I can run that when the engine is off without the low oil pressure alarm screaming at me!
Anyway - moral of the story is this:-
If you disconnect something to work on it and when you reconnect it it doesn't work properly then FIRST thing is check integrity of electrical connections!

Graeme
#366, 1996, Jaskar

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