'67 L79 Temperature Sensor

[Mark S.]

1967 Convertible, 327, 350 hp, 4 speed, No A/C

I am searching for the correct temperature sensor that reads the proper temperature on the gauge. This is the brass sensor that screws into the intake manifold. Can anyone recommend a vendor and a part number?

Thanks in Advance.

[Douglas L.]

Re: '67 L79 Temperature Sensor

Mark - I have found the best are used originals.

[Larry L.]

Re: '67 L79 Temperature Sensor

This has been kicked around for a long time. Before you decide that your sensor is incorrect. Sneek the boss's candy thermometer out and see what the temperature of the coolant really is. Better yet get an optical pyrometer that can read the temperature of an object with out contact. A good thermocouple and calibrated meter work well. Before you shot gun the problem find out what the temperature really is.

If the collant temperature is too high or low get a new thermostat.

Next get a fixed resistor, connect it between the green resistor and ground. This will tell you if your gauge is good.
If the gauge reads correctly - you need a new sending unit.

I will send you the sensor tests and you can pick a fixed resistor that coresponds to a fixed temperature. Use a 2 Watt resistor. You will need three values because the gauge is non linear as the sensor is non linear.

The bad news is that you cannot take a resistamce reading of a sensor at anything but 180 def F and expect it to give you a good reading in the car. In the tests you will notice that the resistance at 94 deg F (hand temperature) does not corralate with the a good / bad sensor.

A while back I tested a bunch of sending units, measured the resistance every 10 deg F, plotted the data and they were all over the map. A know orig. that reads correctly in an orig. car, and several reproductions, some non AC units and some collected from the junk yards. The best was a junk yard find out of an early GMC truck. It worked exactly like the orig in the orig car.

Never use Teflon tape on the senosr because it requires a good ground to operate properly. Try some leak lock or white pipe sealer on first two threads and install it dry. Try not to over torque it.

One other thing to remember is that the sensor contains a thick black oil (I don't know what it is but it looks like oil) so don't immerse it or check the temperature upside down. Normally the sensor is sealed but sometimes they leak when not in the vertical position.

There have been numberous articles and a detailed analysis of the GM source control drawing - that show the allowable characteristics. The therory is correct but the practice some times did not match the drawings.

This is one of the most common problems with the temperature gauges in the early cars.

[Mark S.]

Re: '67 L79 Temperature Sensor

My temp gauge barely moves off the cold position when engine is fully warmed up. I touched the sensor wire to ground with the key on and the gauge went to full hot. I believe that means that the gauge is working.

I bought an Echlin TS6469 temp sensor at NAPA. I have not installed it and I am considering returning it.

Thanks again.

[Jack H.]

Re: '67 L79 Temperature Sensor

Yep, that test proves the gauge is working, but it doesn't prove the gauge is actually calibrated properly... There are many threads on this 'problem' in the archieves but most folks jump to the conclusion ALL of their problems lie in the temp sender.

It takes two to tango...

You need a properly calibrated temp gauge AND you need a temp sender that's within original factory specs. When the temp gauge came off the assy line, it went to a final calibration station where a test operator connected it to a 'ding ding' box (controlled voltage + controlled current), allowed the center shaft to turn and THEN installed the pointer needle to a specific position at the high end of the gauge (red zone, overheat area).

On later temp gauges, the pointer needle was installed during gauge assy and the final test/cal operator picked from a selection of precision wire wound resistors to 'trim' the guage for accurate readings at the high end of the dial. At our shop the first thing we check is the accuracy of the temp guage before diving into replace temp senders by hit/miss...