Replacing coolant temperature gauge

[iframes]

Hi all, I hope somebody can help me out here.

I have a 1984 Thompson Cutlass with a Mercruiser 170 I/O. Really it's my father's boat but he leaves most of the repairs and running to me

One of the (many) issues I have is a temperature gauge that always reads at the bottom of the scale. I tried testing it according to the repair manual. First I disconnected the sender wire, this didn't change anything. Next I jumped the sender screw to the ground screw, this makes the gauge "jump" a tiny amount when I turn the ignition, but that's it. It doesn't go to full. The rest of my gauges work, and all their G and I studs are wired together.

I suspect the gauge itself is bad. I took it out of the console and looked at the model number, it's a "Medallion 8-84". Doing a Google search on this turned up an RPM gauge, which is not what I'm looking for. It appears that this "Medallion" company is long defunct.
My question is, how do I find a replacement part? I have no idea what kind of temperature sender I have, so I don't know what will compatible.

 

[mjf55]

Hello iframes, and welcome to iBoats.

I am not an expert here, but perhaps I can help.
The standard test for a fuel/temperature/oil gauge is to remove the 's' wire and turn on the ignition. The gauge should be to the left.
Now, put the 's' wire to ground and with the ignition back on, the gauge should move fully (peg) to the right. Based on the information you provided, I agree with you that the gauge is bad.

Now, Medallion gauges are NOT out of business ( http://www.medallionis.com/ ), they just see to be in the high end with no information on old products. Perhaps contacting them can shed some light on the gauge.

AS far as matching a gauge to a sender, I have read that is necessary for accurate readings, but I cannot believe that is in every case.. I would suggest that you look for a gauge that you like on iBoats, and call / ask via web if the OEM sender that you have in your Mercuriser would work.

Hope that helps some.