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My civic is still overheating even after replacing the ect switch and thermostat (the fan never comes on).

Shorting the ect switch by putting a paper clip in the connector causes the fan to come on.

What other troubleshooting steps can I take?

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  • Need some more info. Are you loosing coolant? Does the heat work? Is it overheating while sitting, driving, highway, always? When you were checking for the fans to come on, was it overheating?
    – rpmerf
    Jun 1 '16 at 15:14
  • Yes, I am loosing coolant. Heat works. it overheats when I drive 25mph. It did not overheat when I started and had it idle.
    – AWippler
    Jun 1 '16 at 16:37
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    Thanks. You do not need to worry about the fans coming on until it is past half the gauge. Loosing coolant is a big deal and needs to be dealt with first. If you are loosing coolant, then there is a leak. With a leak, you will not be able to build pressure in the coolant system, and your boiling point will be much lower.
    – rpmerf
    Jun 1 '16 at 17:22
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The fact that the fan comes on when the switch is jumped is very useful since this tests the power source, relays and fan motor.

The fans can be activated by either the switch in the water passage near the thermostat housing or the coolant temperature sensor via the PCM (powertrain control module) located in the cylinder head below the distributor. So testing of both sensor and switch may be needed.

The switch should close and turn on the fans at about 199 deg F. Regardless of what the sensor is telling the PCM about the engine temperature. A simple scan tool would be helpful; it would display engine temperature.

Either the new switch is bad or the coolant around it is not getting to 200 degrees. A low temperature in this area could be caused by poor flow in the system.

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  • It is poor flow in the system - head gasket is bad.
    – AWippler
    Jun 3 '16 at 16:20
  • @AWippler Glad to hear you found the problem. Jun 3 '16 at 17:06
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Best recommendation:

  • Purchase a $30 Haynes or Chilton repair manual from your local autoparts store. Best money spent ever. Then follow the troubleshooting guide in your book for "poor cooling".
  • If indeed shorting out that Engine Coolant Temperature (ECT) switch starts the fan and it never works otherwise, then the switch probably needs replacing.
  • For general troubleshooting, a multimeter comes in very handy for all things electrical. You don't have to spend a lot of money on one. You will need this to properly test all things electrical (generally by unplugging a sending unit, and testing for a particular resistance.) The book will tell you how.
  • There are a whole lot of other ideas on troubleshooting engine cooling systems in this forum. Search for [overheating], [coolant], or [cooling-system].

Edit / Update:

So that sending unit isn't an on / off switch, it should be a variable resistance device. Here's an overview.

engine coolant temperature sender

When you read the resistance across the unit, what do you see (in Ohms?) Does that match the chart (in YOUR new service manual) for the current temperature? There are more things than just that sender in the system. When you short it, you are telling the coolant fan control system that the engine coolant is at extremely high temperature, so that really is a lousy test. Its possible the old sender was good, but the control device has problems. (And that would mean, you just wasted good money for nothing.)

Step #1. Buy the manual.

Step #2. Do a methodical test of everything in the system according to the manual.

(I will say, its not clear from your comment. Do you already have the service manual for your car: Make, Model and Year? Do you have a multimeter? If so, apologies from me for assuming that you did not. The service manual will tell you how to accurately verify the correct reading from a temp sensor. Generally you will measure resistance across the terminals when the unit is disconnected from the wiring harness, but follow the instructions in your manual. These all vary a little bit. )

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  • I already replaced the switch. Any chance you could give the voltages they should be? Doesn't seem to be in the service manual.
    – AWippler
    Jun 1 '16 at 5:37
  • @AWippler it's a switch it closes when it hits a pre defined temperature. you'll have ignition voltage on one pin ground on the other.
    – Ben
    Jun 1 '16 at 10:35
  • @zipzit on that year and engine they use a sensor on the radiator and a switch by the thermostat. in this case he's talking about the switch by the thermostat.
    – Ben
    Jun 1 '16 at 10:37

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