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  Water Temperature Sending Unit for Mercury

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Author Topic:   Water Temperature Sending Unit for Mercury
EyeDock posted 05-08-2009 09:43 PM ET (US)   Profile for EyeDock   Send Email to EyeDock  
To upgrade my instruments I bought a Teleflex Lido outboard water temperature guage which comes with the matched sending unit for my 1992 Mercury 115-HP two-cycle motor. I found and removed the existing sending unit, however the new Teleflex unit is just minimally too large (diameter) to go into the existing blind hole. Is it correct the the Teleflex gauge must be matched to the Teleflex sending unit? Would a Mercury sending unit work?

Teleflex was bought by VeeThree last March! Thanks

jimh posted 05-08-2009 11:39 PM ET (US)     Profile for jimh  Send Email to jimh     
Usually an electrically operated temperature gauge has to be matched to the sending unit. However, the Teleflex and Mercury units might be interchangeable. You'd have to compare the resistance of the sending unit. Check them with an ohmmeter.
davej14 posted 05-09-2009 12:34 AM ET (US)     Profile for davej14  Send Email to davej14     
It is not just the static resistance of the thermistor but also the change in resistance vs. temperature. The gauge is going to be matched to the thermistor resistance profile. If the manufacturers are not the same then it is probably not going to give you an accurate temperature reading.
jimh posted 05-09-2009 08:57 AM ET (US)     Profile for jimh  Send Email to jimh     
To "compare the resistance of the sending unit" you'll have to compare them at several places in the operating temperature range. The easiest way to do this is to immerse them in a pot of water and heat the water on the stove. Remove the two sending units and quickly measure their resistance at various temperatures. Or heat them up with a hair dryer to the same temperature. You could check them with an infrared temperature gun.

Or check with Teleflex to make sure you have the proper unit for your motor.

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