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Old 29-12-2007, 21:44   #1
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Temp Gauge/Sender ???

I just replaced the faulty temperature gauge on my Universal M18. The replacement part was a Westerbeek as the Universal part is no longer made. I tested the gauge and it works fine. The problem is, it appears to be reading very low. Is it typical that the temperature sender and the gauge need to be matched up? I'm wondering if the original sender is just not calibrated properly for the the new gauge. I assume that it is very unlikely that a diesel running for an hour would still be sitting at 120F... I have no baseline as the temp gauge wasn't working when I bought the boat.

BTW, Are there any charts that map ohms to temperature for sender units? If most senders were calibrated the same, I assume such a chart could exist?

Thanks!
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Old 29-12-2007, 22:35   #2
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Is your engine salt water cooled? I think most people are shooting for 140 degrees to prevent scaling on salt water cooled engines.


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Old 30-12-2007, 03:16   #3
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Yes, there are two general engine gauge & sender types; North American (open high ohms) and European (open low Ohms). See the Sender resistance chart, linked last.

Basic Engine Gauge Theory & Testing:
http://www.cruisersforum.com/forums/...sting-645.html

Wiring Diagrams:
http://www.cruisersforum.com/gallery...=500&userid=79

Testing Instructions:
http://www.cruisersforum.com/gallery...=500&userid=79

Sender Resistance:
http://www.cruisersforum.com/gallery/showimage.php?i=1624&c=500&userid=79
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Old 30-12-2007, 08:49   #4
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Originally Posted by cal40john View Post
Is your engine salt water cooled? I think most people are shooting for 140 degrees to prevent scaling on salt water cooled engines.


John
It is freshwater cooled.
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Old 30-12-2007, 09:09   #5
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Quote:
Originally Posted by GordMay View Post
Yes, there are two general engine gauge & sender types; North American (open high ohms) and European (open low Ohms). See the Sender resistance chart, linked last.

Basic Engine Gauge Theory & Testing:
http://www.cruisersforum.com/forums/...sting-645.html

Wiring Diagrams:
http://www.cruisersforum.com/gallery...=500&userid=79

Testing Instructions:
http://www.cruisersforum.com/gallery...=500&userid=79

Sender Resistance:
http://www.cruisersforum.com/gallery...=500&userid=79
Thanks Gord. The bottom 3 links didn't work but I found them searching. I guess my sender is bad based on the resistance table. Looking at it, it's hard to imagine a temperature sender failing...
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Old 30-12-2007, 11:13   #6
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Sometimes temp senders can get a little corrosion on them at the sender or the gauge increasing resistance. They can also get loose. Check your crimp connectors for resistance as well. Put an ohm meter across the circuit and see what you are getting.
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Old 13-01-2008, 09:47   #7
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Ok, I checked all the wiring and there were no problems. I replaced the sender... same problem. The highest temperature I could get the diesel up to was 125F (it is supposed to reach 170). This was idling. If the thermostat is stuck open, is it possible that diesel would not eventually warm up? I've had thermostats fail on cars but eventually, the engine does warm up.

Are there any other possible sources for the diesel not reaching operating temp?

Thanks.
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Old 13-01-2008, 11:58   #8
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Indeed. If the thermostat was faulty, the engine would easily not come to temperature. That would be my first place of try, before I suspect the gauge/sender. It is common for states to fail, far more common than the guage or sender.
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Old 13-01-2008, 12:20   #9
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Indeed. If the thermostat was faulty, the engine would easily not come to temperature. That would be my first place of try, before I suspect the gauge/sender. It is common for states to fail, far more common than the guage or sender.
Thanks Alan. It still amazes me how harsh the marine environment must be for the amount of stuff that fails on sail boats. If I replace the thermostat, that'll be the third component to have failed in the path to getting the temperature gauge functional. First, the gauge had a bad ground. Replaced the wire. Next, the gauge was faulty. Replaced the gauge. Then, the gauge finally started working but read low (125F max). I suspected a bad sender since it was all corroded. Well, that was a waste of money. Anyway, I hope a new thermostat solves the problem. After that, it'll probably be some oil pressure relief valve or something

Are these cascading failures signs of poor maintenance by the previous owner or just a signs of a 20 year old boat?
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Old 13-01-2008, 21:22   #10
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Are these cascading failures signs of poor maintenance by the previous owner or just a signs of a 20 year old boat?
A bit of both really. 20 yrs is a long time in a marine environment. Every single component on a boat, especially in the engien compartement, needs special regular attention to make it last 20yrs and beyond. The thermostat is just one of those things. So fail, some don't. Corrosion is poor maintenance. Faulty gauge is just one of those things also. The sender shouldn't have cost too much, so I don't think it is a wast of money. It does help solve the problem due to elimination. I bet you would ahve happily paid someone the coat of the sender if that was all it took to elliminate the possibilities.
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