pretty sure it is electrical....maybe...

[bob johnson]

1995 Johnson 115hp. I got a temp sender in each head they are identical .

I have one temp guage ( omc) and I have a Cotura on -off-on switch to use to send a signal from either head to the guage .

it had been working fine...but once in a while once side wont send....ie i am getting a no reading.

this weekend the one side that seems to always work was running up to about 215 degrees!!! i was worried i was over heating.. the other sending wasnt sending, when I switched it over...if i ideled the temp fell to about 180, if i ran about 2500 the temps went up to the 200-215 range, when i ran 4000 rpms or more, it fell back to 180ish..

but...

once the other sender started sending......the temps in the hot side, never went above 180 and both heads were running in the right range....160-180 ish

I had pulled the cover and checked each head with my hand when i was getting the 215 reading and they both seemed about the same...I could eaily touch but not hold it on for much time.

so when BOTH senders were sending fine..the temps were right, once one stopped sending( for what ever reason) the other one went high!!!!!!!

and when the second started again...the one that was high fell back to normal...

it is possible, I have a bad switch( thus electrical question)

I am thinking they are seperate....i have individual wires running from the senders to my switch....so one does not know what the other is doing!!

so i am thinking my senders are fine...and the guage reads ok when both are working.....

anyone run into something like this before?

thanks

bob

 

[wire2]

Re: pretty sure it is electrical....maybe...

If you have a volt-ohm meter, you can test the wiring and the senders. A temperature sender is a variable resistor that changes with temperature.

Put the tester on Ohms X 10, place 1 lead on ground, the other lead on the wire from 1 sender that's NOT switched on to the gauge, and with the key off. Then move the switch to the other bank and read the alternate sender. (with the switch on bank A, read sender B, then move the switch to bank B, read sender A)
The readings should be virtually identical. If not, undo the wires from the senders at the heads, take a reading from the sender posts to the head. Again, the 2 readings should be identical. An open, erratic, or shorted sender is defective.

 

[Tacklewasher]

Re: pretty sure it is electrical....maybe...

Sounds suspiciously like a ground problem to me.

Check the wiring and clean the connections.