Temperature Gauge Question [Archive] - Chevelle Tech

: Temperature Gauge Question

Jun 16th, 10, 11:03 AM
Posted this problem inside another thread, but it is most appropriate here.

The temperature gauge on my '67 SS is not working properly. We grounded it out and the gauge responds properly so we believe it is the sending unit. The needle on the gauge barely gets past the 'C' when hot. Where should it be for a normally functioning unit at normal operating temperatures (1/4, 1/2, 3/4 or ?).

Also, the hot engine light on the dash is faintly on. We were thinking that there is possibly a grounding issue where the light is getting a small amount of power enough to glow it a bit. Is there any possibility that the sending unit could be affecting this? On other cars I have seen two sending units, one on the block and one on head. Does a '67 have this or is it only one that runs both the guage and the light?


Jun 16th, 10, 2:07 PM
Most stock thermostats are rated at 195*. So if you can judge where that reading would be at on your gauge that is where your avg temp reading should be.

Jun 16th, 10, 3:09 PM
Make sure the sending unit is making good connect with the head, assume that's where it's mounted. If you wrapped the sending unit up in teflon tape or something it may not be making good contact.

Jun 16th, 10, 3:58 PM
There are no numbers on the stock gauge, so I can not tell what temperature the needle represents, regardless of where it shows. This is why I am asking where do normal ones sit. So if the car is running normally and I can measure the temperature of the area around the sending unit using an infrared temperature tool, let's say that turns out to be 195F, on a gauge with no numbers, where would the needle normally point (middle of the graduated area, lower half, upper half, etc. )?

The sending unit I'm talking about is the one mounted in the intake. I've looked all around and see no other sending unit. I just got the car and I have no idea whether this is a stock setup or whether people have changed things. I just wanted to know if stock setups use one or two sending units and which one runs the gauge and which one runs the warning light, if it is set up that way.

Thanks again.

Jun 16th, 10, 4:24 PM
The 67 temp sender is mounted on the intake manifold. The sender didn't move to the cylinder head until the 1968 model year. With a factory gauge setup normal operating temp would be between 1/4 and 1/2 up the scale depending on the thermostat you have (160, 180, or 195).

As noted above, there should be tape or sealant on the threads of the sending unit or the hole that would cause the sending unit NOT to ground as it should. Here's an excellent explanation of how an electric temp gauge works.

Basically, an electric temperature gauge is a voltmeter. The scale on the gauge face is reading temperature but the instrument itself is reading voltage. The gauge itself is comprised of a bimetallic (two different metals fastened together) "hairpin" assembly. This assembly is attached to the needle.
The gauge requires an electric circuit and a sending unit in order to read temperature. The sending unit is a temperature-sensitive material that is part of a variable resistance, water-sealed unit that sits in the coolant stream in the engine. As the engine warms up the resistance in the sending unit is lowered gradually until the system reaches maximum heat. The sending unit is the "ground" portion of the circuit.
In the completed circuit the battery voltage passes from one side of the gauge, through the bimetallic spring and onward to the sending unit, which is grounded to the engine. When the engine is cold the resistance is high, so little current passes through the gauge. This small current doesn't heat up the bimetallic spring, so the gauge reads a low temperature. As the engine warms and the sending unit's resistance lowers more current passes through the gauge and the needle reads higher and higher because the bimetallic spring expands further. Electric gauges can fail to read accurately because the sending units fatigue or rust over, or simply lose their connection to ground. The bimetallic spring can also fatigue over time, rendering the gauge inaccurate or inoperable.

Reference page http://www.secondchancegarage.com/public/653.cfm.

I believe the sending unit for a warning lamp is different from a sending unit for the electric gauge so it may have the wrong sending unit. The correct gauge sending unit fits 66-68 regardless of V8 engine size as the gauge option could be ordered with any V8 - did NOT have to an SS396 to order gauges.

Jun 16th, 10, 5:12 PM
1967 cars used a 180 degree thermostat. Generally the temp needle will position itself about the middle of the gauge when completely warmed up. This is assuming the gauge and sending unit are working properly. You could have a sending unit going bad.

Jun 16th, 10, 5:50 PM
The factory gauges worked poorly in both my 69 Malibu and my 64 C10. I was using sending units bought at local auto part stores. Based on advice I got here at TC, I bought new sending units from Lectric Limited, and now both gauges work perfectly.

Jun 16th, 10, 8:24 PM
1967 cars used a 180 degree thermostat.

According to my 1967 references, non A.I.R. Chevelles came with 180 stats while those with A.I.R. came with 195. :)

Jun 16th, 10, 11:36 PM
Can someone look at this and tell me if it looks like the right one. When I go Ecklers website, for example, it show the sending unit with a horizontal flat disk at the top for a car with gauges. It shows the one that I have with the vertical flat tab for the cars without gauges. So it looks like this the one I have is the wrong one.

However, when I look at the wire connector for this, I can not see how the connector on the wire will connect to the sending unit with the flat disc at the top. Do I have the right wire connector?


Jun 16th, 10, 11:56 PM
Judging from the type of fitting on the temp wire, you need a sending unit that uses the post, and not the spade.

Jun 17th, 10, 1:00 AM
Got some answers in the archives. The sending unit is wrong and so is the connector. The sending unit that I need has the "nail head" type terminal at the top and I need a different connector to connect to it.

I know what to do now. Thanks for the help.