Temp gauge prob - 73 Johnson OB

[Fair Boater]

I have a 73 Johnson 115 OB with a temp gauge in the dash that doesn't register (stays at low-temp side of gauge). I assume (man, I HATE that word) the gauge to be original as it matches the others in the dash.<br />The gauge is properly grounded, as the running light operates. I have cleaned and reset all connections. Is there an easy way to test the gauge? <br />The gauge's "sender" wire is soldered to a wire that runs between two "temp-sensors" in the bottom two cylinders. <br />Can someone explain how the temp system is supposed to operate? The owner's manual states that the temp-sensors act as a switch for a temp alarm horn. If this is the case, how does the sending wire receive a variable reading for the gauge?<br />A voltmeter connected between the solder joint and ground (also between "sender" terminal of gauge and ground) reads +12V with the ignition on, motor running. This reading never changes.<br />Any help is appreciated in advance! Thanks for reading this novel!<br />Bob

 

[rwise]

Re: Temp gauge prob - 73 Johnson OB

Fair Boater <br />In general, the gauge will have power supplied to it from the battery, then run to the sending unit. The sending unit is open (will not pass current) until it heats up the it starts to pass some current, this causes the temp gauge to rise. If the send unit/s are not the correct type for the gauge they will not work correctly. If the sending unit is for an alarm it will close at a set temp. If you can remove the wire from the sending unit you can use an ohm metter to test it. With the engine cold you should get a high reading as the engine warms up the reading should change to a lower reading. Hope this helps!<br />Richard

 

[wilde1j]

Re: Temp gauge prob - 73 Johnson OB

The temperature gauge sender is almost always separate from the hot horn temp switches. The sender is usually threaded into a recess on one bank of a V4 or V6. Typically the sensor is a thermistor or thermocouple. It may be that the hot horn switches have gotten connected to your gauge, which is useless. Look for a sensor threaded into the cylinder head with nothing attached and check out the existing wiring, as your hot horn may not be functional. Most OMC V4 and V6's use tan wires from the hot switch to the horn. You can check operation by grounding either one (or both individually).<br /><br />The temp gauge sender is in addition to the hot horn switches.

 

[kart33]

Re: Temp gauge prob - 73 Johnson OB

Fair,<br /> Teleflex.com has a troubleshooting section online that is wonderful. It will tell you how to test the gauge and show you the needed sender.<br />My 1985 V4 90HP Rude has an external Z bracket mounted on a head bolt that the sender screws into. This set up is great and the sender is only $8.00 at your local OMC part dealer. Good Luck!

 

[Fair Boater]

Re: Temp gauge prob - 73 Johnson OB

Thanks to all for the help on this one! I'll check out the info I have gathered this weekend! <br />A special thanx for the Teleflex.com reference. The site is kind of tough to find things in, but the info is excellent once you find it!<br /><br />Bob