Water temp/ oil temp gauges fault finding

[williamp]

My car has both. The oil temp gauge has stopped working, but I dont know if it is the sensor (on the sump) or the gauge. So:


1) Can I swap the feeds into these dials, so the water temp shows oil temp and vice-versa? This way I could eliminate whether its the gauge, or the sensor. Will this work, or knacker both dials?

Both dials are smiths, by the way

[yellowvette]

Can't see how it would damage the gauge doing what you suggest. I would do it when cold then watch the gauge as the car warms up. On my Vette I know I can check the temp gauge by grounding the wire to the sensor - it gives a full reading - yours should be OK with this too, but of course I take no responsibility etc.etc.

[M3 Mitch]

In general, the sending unit fails much more often than the gauge. Pull the sending wire off the sending unit, and check resistance from the sending unit to ground, I will bet it has infinite resistance.

While you have the wire disconnected, connect a test light (just to provide some resistance, it's not really necessary) between the sending wire and a ground, then jump in the car and turn the key to "on" (no need to start the car). Unless the gauge itself is bad (again, this is rare) you'll see the gauge go upscale. As soon as you see the gauge move, you can rest assured the gauge is good and the sending unit is bad.

[williamp]

M3 Mitch said:

In general, the sending unit fails much more often than the gauge. Pull the sending wire off the sending unit, and check resistance from the sending unit to ground, I will bet it has infinite resistance. While you have the wire disconnected, connect a test light (just to provide some resistance, it's not really necessary) between the sending wire and a ground, then jump in the car and turn the key to "on" (no need to start the car). Unless the gauge itself is bad (again, this is rare) you'll see the gauge go upscale. As soon as you see the gauge move, you can rest assured the gauge is good and the sending unit is bad.

Thanks for this. I did as you advised, and you're right: the gauge is fine, but sender unit isnt. Many thanks