Temp Gauge Repair

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Original Submission by T Oct 29th 2006;

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HZ Fuel and Temperature Gauge. Photo by Onlyholden. Click to Enlargen.

Faulty Temperature Gauge:

If the Thermal Temperature Gauge on an HQ - WB or up to a VK Commodore doesn't read correctly the problem can be that the Gauge's internal resistor has blown.

Temperature Gauge Under Reads:

Adding a Resistor in Parallel:

 

Symptoms:

Symptoms are that the Gauge will show a positive deflection if the Sender wire is connected to ground but the Gauge itself barely moves when connected to the Temperature Sender even if the Engine is up to Temperature. Replacing the Temperature Sender does not fix the problem.

HZ Temperature Gauge showing the internal 36 ohm 1 watt bias Resistor. Photo by Red Seat. Click to Enlargen.
HZ Temperature Gauge showing the internal 68 ohm 1 watt Resistor. Photo by Red Seat. Click to Enlargen.
HZ Temperature Gauges. Left Panel Van, right Sedan. Photo by Jesse Hughes. Click to Enlargen.
 
Aftermarket Temperature Gauge and Sender (left) HQ Dash Light Sender (right). Click to Enlargen. Photo by SeanWalsh.
HZ Temperature Gauges. Left Panel Van, right Sedan. Photo by Jesse Hughes. Click to Enlargen.
 
Gauge type Temperature Sensor Adaptor for red Engines. Image by MyEHHolden. Click to Enlargen.
 
Gauge type Temperature Sensor on a 202 UC (top right). Note that the Sensor is screwed into the Adaptor. Click to Enlargen. Photo by T.
 
On blue/black Engines the Dash Gauge Temperature Sender is mounted at the rear of the Engine on the offside. Click to Enlargen. Photo by Phillip Gard. 
 

 

The Cause:

The problem is caused by a failure of the Temperature Gauge's internal Resistor.
This Resistor can fail with age but is often caused to fail because it shares a harness with the pink supply line that leads to various parts of the Engine. The pink supply carries 12 Volts and is fed from the Ignition Switch. Sometimes the pink wire can come in contact with the Temperature Sender Wire and push 12 Volts directly into it.
The result is that the Internal Resistor in the Temperature Gauge becomes blown by the excessive power through it.
The Resistor is there to provide a bias current for the Gauge. Without bias current the Gauge will heavily under-read.

The Fix:

The fix is to fit an external Resistor in parallel with the Temperature Sender Wire. This Resistor should be 36 Ohms 1 Watt. 33 and 39 ohm 1 Watt Resistors will work too. TemperatureGaugeRepair1.jpg
Use a red Crimp Lug on each end of the Resistor. Connect one end to a good earth on the chassis and the other end to the Temperature Sender Wire.

Gauge Type Temp Sender:

Hi Guys. The original Holden temp sender units were made by a company called Flexdrive, who made many gauges & senders for Holden over many years. Equivalent VDO temp senders are still available for all models except HD/HR X2. The VDO part number for the HJ/X/Z temp sender is 320.003. The adaptor from 1/2"NPT to 1/8" NPT is 320.053. Both these are currently available. Both threads are NPT NOT BSP. BSP is close, but not close enough for a good fit. Dr Terry.  

Calibration:

Don't heat the Sender above 100 deg C.

 
Temperature
 Resistance
52 deg C
 282 ohms
  60 deg C  217 +-36 ohms
 100 deg C  67 +- 11 ohms
 123 deg C  40 ohms
   
 
 Gauge Needle Position  Resistance
Cold 
282 Ohms
 Half  74 Ohms
 Hot  40 Ohms
   

 

Voltage Regulator:

The factory fitted Dash Voltage Regulator is a Thermal BiMetal Strip type Device that can burn out. When it does burn out, the Temp and Fuel Gauges permanently read Zero. The factory Regulator can be replaced by a 7805 Solid State Regulator which is much more reliable and easily bought from Jaycar Electronics. Details for wiring the 7805 are in the Photoshoot. Many thanks to OH Member Onlyholden for testing and fine tuning the Gauges using a 7805 and posting up this info.

G,day all, i,am at it again the electric regulator needed for the hz looks to be the 7805 5 volt output, installed today gauges seem to be on the mark End of submission by Onlyholden.

Temperature Gauge Misreads:

See the Electrical Gauge Calibration page for details on how to remedy this.

Links:

See the Fuel Gauge Page for how to repair the Voltage Regulator

Temperature Indication:Faulty

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Terms:

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