Looking for info about temperature gauge and sender

[dmjlambert]

I wonder if somebody here knows some info about temperature gauges and senders.

I have a 1969 CST/10 with the original 350 engine rebuilt and stock instrument cluster with gauges.

At first I thought my temperature gauge was dead, but I got to poking around, and after cleaning up the terminal at the temperature sender on the driver side near plug 1, I noticed the meter does move a little bit as the engine warms up. I touched the sender wire to ground and it pegs the gauge, as I expected.

When the engine is warmed up and I see coolant flowing in the radiator, the temperature gauge reads in the cold range, almost in low side of the normal range. I disconnected the sender wire, and connected an ohm meter between sender and ground and found it reads 200 ohms with the engine warm and running. Is that too many ohms to get a good middle reading on the temperature gauge?

I am thinking of removing the sender and doing a test with it with a pot of water on the stove, and see what it reads at various temperatures. It may be a sender for a different gauge, I don't know. What size and type of plug could I block the hole in the engine with, so I don't end up draining all my coolant just for some testing?

I'm not extremely familiar with my engine, as the thermostat was installed by the engine builder, and I have not pulled and tested that yet. But I plan to.

I'm just looking for snippets of information, and wondering if anybody has made a temperature to ohms chart for the stock setup of our trucks. Does anybody bother to test the temperature sender in a pot of hot water on the stove? Any tricks or tips to making sure the setup is good and ready to help me avoid overheating my engine?

[davepl]

I have both the factory one and the results from when I tested my own in a pan on the stove. Attached.

[dmjlambert]

Great! Thanks, that is fantastic info. I will measure the actual temperature of my coolant or engine and if it is actually running at about 180 to 200 degrees, I will replace that sender because 200 ohms would be wrong for that temperature. Look at that beautiful marble countertop!

[garyd1961]

Am I wrong or don't most run on the low side of normal? I know I have seen several trucks running like this.

[dmjlambert]

Perhaps. In my case the gauge reading is in the cold range and I can barely tell the gauge has a reading at all.