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Electric Cooling Fan Problems Part 6

It's not quite summer yet and I'm seeing cars come in with overheating problems. Here is how you can avoid coming into my shop with this problem.
» Part 1: Getting Hot Out
» Part 2: How They Work
» Part 3: Now What?
» Part 4: The Fan Motors
» Part 5: Coolant Switch
» Part 6: Coolant Sensor
» Part 7: Cooling Fan Relay

You have to check it with an ohmmeter. The thermistor has lower resistance at higher temperatures and higher resistance at lower temperatures. If the CTS has a resistance of 1500 ohms with the engine at normal operating temperature, the CTS is out of calibration and needs to be replaced. Service manuals will have a chart as to what the resistance should be at different temperatures.

For example, from the 1995 Chevrolet Lumina V-6 3.4 liter DOHC service manual:

Engine Coolant Temperature (ECT) Sensor
100°C (212°F)177 Ohms
90°C (194°F)241 Ohms
80°C (176°F)332 Ohms
70°C (158°F)467 Ohms
60°C (140°F)667 Ohms
50°C (122°F)973 Ohms
40°C (104°F)1,459 Ohms
30°C (86°F)2,238 Ohms
20°C (68°F)3,520 Ohms
10°C (50°F)5,670 Ohms
0°C (32°F)9,420 Ohms
-10°C (14°F)16,180 Ohms
-20°C (-4°F)28,680 Ohms
-30°C (-22°F)52,700 Ohms
-40°C (-40°F)100,700 Ohms

» Part 1       » Part 2       » Part 3       » Part 4
Part 5       » Part 6       » Part 7
Additional Information provided courtesy of and Warranty Direct
© 2000-2007 Vincent T. Ciulla

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