by: Richard Schmidt
TROUBLE SHOOTING EGT and WATER TEMP
A high quality volt/ohm meter is required for these test. Especially for the calibration check.
EGT
No or low readings
A. To check the sender,
1. Make certain all connections are clean secure.
2. Reverse connections to see if this is the problem.
3. Disconnect sender from gauge, check the resistance of the sender. A cold probe on the sender should be
approx, EGT 2.5 ohms.
NOTE: be sure to zero out your ohm meter if possible. If not, note the actual reading when you short the ohm meter leads together. You will most likely see about 0.3 to 0.5 ohms with the leads shorted. When you measure your probe, subtract the residual reading from the probe resistance.
4. Use the ohm meter to check for wiring shorts to the probe housing. Most probes are not the shorted kind,
so you should get infinity ohms between both probe leads and the probe housing.
NOTE: when checking for shorts, with the meter connected, move the probe wires around were they exit the probe to check for intermittent shorts.
B. To check the gauge. Note: this applies to non-electronic gauges. However it should work for electronic gauges as well. USE OHM METER ONLY FOR THIS TEST!
1. Disconnect the gauge from the sender, check the resistance of the gauge. Depending on the scale sent on the meter, the resistance will be between 8 - 15 ohm. You will also notice a needle deflection on the unit.
To check probe accuracy.
Tools needed:
Propane torch
Digital volt meter with test leads
In order to measure the probe and gauge accuracy, you will need to find a way to connect to meter leads to the EGT probe wires while the probe is still connected to the gauge. You may find it helpful to get some of these:
- EZ hook.PNG (88.94 KiB) Viewed 10949 times
1. Remove the probe from it’s location in the exhaust pipe.
2. Set the digital volt meter to read Milliavolts, DC. (Direct Current)
3. Connect the volt meter leads to the probe connector at the gauge. With a digital meter, polarity will not mater, however if you have the leads reversed, the meter will read in the negative direction. It does not matter, the voltage reading will still be accurate.
4. Power up the gauge
5. Start the propane torch and set it to a medium flame.
6. While watching the meter, slowly bring the probe into the flame of the torch.
7. Use the chart below to determine if the probe/gauge is operating properly.
PROBE TEMP (°F) . . . . VOLTAGE (MV)
200 = = = = = = = = = = = = = 2.87
600 = = = = = = = = = = = = = 11.91
800 = = = = = = = = = == = = 16.58
1000 = = = = = = = = = = = = 21.31
1200 = = = = = = = = = = = = 26.03
1400 = = = = = = = = = = = = 30.70
Disclaimer: As with any use of open flame in a shop, one must be very careful around flammable materials.
NOTE: Some times the EGT probe and the connections to the display gauge can be crossed up causing no end of confusion. A simple way to check to see if your left cylinder and the left display are connected properly is to disconnect the probe wires from the display and then run the engine. You should only see any increase in displayed temp on the right cylinder.
WATER TEMP
A. To check the sender.
1. Make certain all connections are clean and secure.
2. Disconnect the sender leads from the gauge, cool or heat the probe to a known temperature, the check the resistance. See chart below.
Water Temp (°F). . . . . . Probe resistance (ohms)
32 = = = = = = = = = = = = = 9800
70 = = = = = = = = = = = = = 3570
100 = = = = = = = = = = = = 1740
150 = = = = = = = = = = = = = 615
212 = = = = = = = = = = = = = 212
B. To test the operation of the unit, disconnect the sender leads from the gauge and substitute the sender with a resistor of the appropriate value that you wish to check from the list above. Such as 615 ohms is 150°F
C. If the sender lead goes to ground, the gauge should peg full scale.
D. If the sender lead is open (broken) or the sender is open internally, the gauge should go to full scale. Slight gauge indication to the lowest reading is normal when the temperature is below the starting point of the gauge.