Temp gauge started reading about 120

[Green_Giant]

Hi,

All of a sudden, the temp gauge started reading low, but the boat seems to be up to proper operating temp, based on feeling the engine and using the hot water shower full hot, so I'm pretty convinced this is a gauge thing. I pulled the cannon plug and cleaned / re-installed, no change.

I've isolated to the proper sender (red arrow in the picture) is this the sort of thing that goes partially bad all of a sudden? Any way to test using a multi-meter? (there are 2 wires for this one versus the standard one tan wire for the other temp sender. Hope it's a connection / sender versus the gauge. Any guidance on where the gauges are gounded out so I can check the ground? Other tips?

Thanks!

Edited June 29, 2008 by Green_Giant

[NorCaliBu]

1st thing I'd do is pull the sending unit to make sure that you don't have either corrosion build-up or even a small piece of debris acting as an insulator keeping the sending unit from transmitting the true temp.

[Green_Giant]

That was a good first place to check / easiest too. I pulled it and all seemed pretty clean. While off I brought it in and did a resistance check on it in cup of cold / warm / hot water using my wife's meat thermometer (shhhh) sending unit checks out fine.

Could try the cannon plug again, what do you guys do to clean those things out? There may be a little corrosion on the pins that I tried to scrape off with a small screwdriver. Anything to spray in there or any solution good for cleaning off mild corrosion?

[VinRLX]

Vinegar or Pepsi. Let is soak.

[NorCaliBu]

...Pepsi.

Ya, the corrosion will just melt away...just like Jack's teeth did.

Let is soak.

[electricjohn]

The temp gauge and the oil pressure gauge operate at a lower voltage than everything else that passes thru the cannon plug. The voltage, only 5 volts, originates from the MMDC, not the battery's 12 volts. The current is very low too (millianps). These two points of the cannon plug need to be clean for a good sound electrical contact. Even though the voltage is much lower than the battery voltage, the senders are normal automotive senders and the MMDC is calibrated to work with them.

[VinRLX]

...Pepsi.

Ya, the corrosion will just melt away...just like Jack's teeth did.

Let is soak.

You're just jealous because I didn't have all my teeth knocked out in high school. . .

[NorCaliBu]

You're just jealous because I didn't have all my teeth knocked out in high school. . .

Only because you never made it out of 3rd grade.

[VinRLX]

Ok, now that's funny right there. I don't care who you are.

[Green_Giant]

that was funny.

Oh, and the vinegar fixed it. Back pegged on 160. :-)