The Pantera Place
"Your de Tomaso Connection"

The Pantera Water Temperature Gauges

 By Bill Taylor

Traditional electrical meter movements consist of a pointer attached to a coil of wire which is suspended in a permanent magnet field and positioned at zero by a spring. As current flows thru the coil of wire in proportion to the parameter being measured, the magnetic field in the coil of wire interacts with the permanent magnet field to move the pointer against the pressure of the spring.

 SOBill Veglia Temp Fig 1.JPG (62816 bytes)

(Fig. 1)

 The early Pantera, 230 degree, temperature gauge shown in Fig.1 operates in a completely different fashion.

 SOBill Veglia Temp Fig 2.JPG (43580 bytes)

 (Fig. 2)

A disassembled Pantera temperature gauge is shown in Fig. 2. The internals of the gauge consist of two coils of wire, oriented at 90 degrees to each other, and a pointer with a small bow-tie shaped magnet attached.

 SOBill Veglia Temp Fig 3.jpg (84861 bytes)

 (Fig.3)

The circuitry of the Pantera temperature gauge used in early cars is shown in Fig. 3. Battery power is applied via the terminal marked “+” to the end of one coil, the opposite end of which is connected to one end of the second coil. The opposite end of the second coil is connected to chassis ground. The point where the two coils are connected together is brought out of the gauge on the terminal marked “TERM.” The terminal marked “TERM” is wired to the temperature sensor in the engine water supply. With the temperature sensor disconnected from the gauge and the battery voltage applied, the terminal marked “TERM” will have a voltage of approximately +5.3 VDC (~45% of the battery voltage). With the temperature sensor connected to the terminal marked “TERM” and the battery voltage applied, the terminal marked “TERM” will have approximately +3.6VDC when the engine is cold.

 Since the two coils are oriented at 90 degrees to each other the current passing thru the coils establishes a magnetic field orientation which determines the position of the pointer. As water temperature in the engine rises, the resistance of the temperature sensor decreases. This sensor resistance decrease causes more current to flow thru the first coil and less current to flow thru the second coil. This change in relative coil currents causes the combined magnetic field of the two coils to rotate. The pointer follows the movement of the magnetic field.

 The following data was measured on an early Pantera 230 Degree temperature gauge:

 Gauge          Sensor Current       “TERM” Voltage       Sensor Resistance

 90 F                .0333 Amps               +3.36 Volts DC         100.1 Ohms
Mark #2          .0443                          +2.71                          59.9
160 F              .0581                          +1.89                          31.1
Mark #4          .0700                          +1.17                          14.8
230 F              .0800                          +0.56                          7.0

 SOBill Veglia Temp Fig 4.JPG (51231 bytes)

 (Fig. 4)

 A late Pantera, 260 degree, temperature gauge is shown in Fig. 4.

 SOBill Veglia Temp Fig 5.jpg (90244 bytes)

(Fig 5)

The circuitry of the Pantera temperature gauge used in later cars is shown in Fig. 5.  The later version Pantera temperature gauges reads to 260 degrees full scale. In addition, the later gauge has had a 10 Ohms resistor added to the chassis wiring between the “TERM” terminal and the  temperature sensor in the engine.

 The following data was measured on a late car, 260 deg temperature gauge:

Gauge            Sensor Current         “Term” Voltage     Sensor Resistance + 10 Ohms

Mark #1          .0392 Amps               +2.99 Volts DC         77.3 Ohms
Mark #2          .0457                          +2.54                          55.6 
190 F              .0597                          +1.62                          27.1
Mark #4          .0648                          +1.27                          19.6
260 F              .0679                          +1.04                          15.3

The following data was measured on a second late car, 260 deg temperature gauge:

 Gauge                        Sensor Current         “Term” Voltage         Sensor Resistance + 10 Ohms

Mark #1          .0332 Amps               +3.32 Volts DC         100.0 Ohms
Mark #2          .0407                          +2.790                         69.0  
190 F              .0578                          +1.766                         30.5
Mark #4          .0646                          +1.31                          20.3
260 F              .0692                          +0.984                         14.2

 Based on a sample of two items, the data shows that individual temperature gauges can vary by approximately 20 % in the current required to indicate the same temperature on the dial. In addition, the “Term” voltage applied to the sensor can vary approximately 11%. The combination of these variables resulted in 29% higher sensor resistance required for the second gauge to indicate an identical temperature as the first gauge.

 Temperature sensors of the following brands were acquired for the following 351C equipped cars :

 Niehoff  TS25571 1973 Torino (Kragens)

Niehoff  TS 25621 1973 Cougar (Kragens)

BWD      WT386  1973 Torino (Pep Boys)

Borg-Warner WT324  (link via Amazon .com)

The four sensors were tested in an oven over the range of 78 to 260 degrees F. and the results, with the data from an OEM Pantera (Ford?) sensor, are plotted in Fig. 6.

 SOBill Veglia Temp Fig 6.jpg (81087 bytes)

 (Fig. 6)

The OEM Pantera sensor was tested over the range of 75 to 207 degrees F. at an earlier date. The upper temperature was limited to 207 because that was the boiling point of water under the conditions of the test.

In addition, Fig. 5 shows the OEM sensor plus 10 ohm resistance and the resistance requirements for the Veglia 260 degree temperature gauge.

The results of this testing show that the OEM sensor, even with the 10 ohm in-line resistor is a very poor match to the Veglia gauge. The OEM sensor with the 10 ohm in-line resistor causes the gauge to read lower than the actual temperature up to approximately 180 degrees F. and then causes the gauge to read higher than the actual temperature. Without the 10 ohm in-line resistor, the OEM sensor is an even worse match to the Veglia gauge.

The TS25621 and TW368 are completely unsuited to the Veglia gauge as they will make the gauge read low with respect to the true temperature over the full range of interest.

Note that even though the TS25571 and the WT386 are listed for a 1973 Torino 351C engine, they have grossly different characteristics.

The WT324 and the TS25571 are available replacement sensors which provide a good match for the requirements of the 260 degree Veglia gauge if the 10 ohm resistor in-line with the gauge is removed. With either the WT324 or the TS25571, the gauge will read lower than the actual temperature until approximately 145 degrees F. and then the gauge will read approximately the correct temperature to 260 degrees F. Accurate gauge readings with the WT324 or TS25571 require that the 10 ohm in-line resistor be removed. If the 10 ohm in line resistor is not removed, the gauge will read colder than the actual temperature over the full range of interest.