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  • Radiator Fan

    Looking for some advise. I have wired my fan up as per the diagram by James in New Zealand. The fan switces off as soon as I turn of the ignition, is this supposed to happen ??
    Last edited by Dopeshow; 25-09-2020, 10:09 AM.

  • #2
    No. It should be on a permanent feed with a relay switched by the thermostat. Did mine by the same diagram and works fine.

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    • #3
      Originally posted by smiffy85 View Post
      No. It should be on a permanent feed with a relay switched by the thermostat. Did mine by the same diagram and works fine.
      Just semantics, but it's controlled by a thermo switch, not the thermostat. I use this one ( Mishimoto Fan Switch 80C - MMFAN-SWITCH ) that comes on at 176 degrees F
      Attached Files

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      • #4
        Sorry. Rushing to reply as tea was ready. Temp sensor operates the fan via the relay was what I was meaning to post.

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        • #5
          Originally posted by smiffy85 View Post
          Sorry. Rushing to reply as tea was ready. Temp sensor operates the fan via the relay was what I was meaning to post.
          I have it wired to a perminant feed, however its switched via an earth through the water temp switch, but also from the ECU from A12. As the ECU turns the fan off as soon as you get over a set speed, this must be another earth trigger point, so I was assuming when I turn off the ignition I lose the earth hence the fan switching off.

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          • #6
            Originally posted by Dopeshow View Post

            I have it wired to a perminant feed, however its switched via an earth through the water temp switch, but also from the ECU from A12. As the ECU turns the fan off as soon as you get over a set speed, this must be another earth trigger point, so I was assuming when I turn off the ignition I lose the earth hence the fan switching off.
            Gents, thanks for your replies. I've finaly got my head round this. So accoriding to the Diagram the fan relay is switched via an earth which is wired through the water temp switch in your block and also from the ECU using A12. as i've only run the car ticking over I have the temp set to 175'f in the ECU, my temps while ticking over never exceed 180'c, hence why when i kill the engine I lose power to the ECU and I lose my earth and the fan switches off. The temp switch located in the head will trigger the fan at 196-203'f so the fan will only ever run when the engine has been killed at this temperature. The standard Honda thermostat doesnt open till around 180'f so im going to increse the fan switching temperature in my ECU. Not sure if this infomratin is helpful, but just thought I would share incase anyone wanted to know..

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            • #7
              Here’s my understanding of how the whole thing works.

              Honda engines normal operating range is around 88C 190C not the 165/175 of yester year. Also in their infinite wisdom Honda called both these components an ECT, the only difference: one is a switch the other a sensor.

              The ECT (Engine Coolant Temp Sensor) (a 2 pin connector) is located under the distributor, alongside the single pin connector for the temperature gauge. The 2 pin (ECT sensor) is used by the ECU on pin D13 which produces a produces a 5v reference signal to this sensor. The resistance in the sensor changes with temperature which changes the reference signal of the ECU. That changes the fuelling/timing MAP in the ECU. If this part fails it will throw a Fault Code 6. (six rapid blinks of the Check engine light).

              The other ECT (Engine coolant temp SWITCH) (also a 2 pin connector) is located on the Thermostat housing. It does not throw any fault codes if it fails. It trips between 91C & 95C (196-203F). That action grounds the coil of the fan relay. It also provides a signal to A12 of the ECU that the fan is running. The ECU is supposed to raise the RPM slightly to compensate for the current draw. Once the coolant temp drops by around 10F, it stops the fan as the ECT switch opens again.

              James wiring diagram uses a permanent power source which should continue to run the fan (once the switch is closed) even with the ignition switch off. Unlike HONDA, which wires the coil side of the relay through the ignition switch, so it only operates when the ignition is on and the ECT switch is closed.
              Last edited by 250ptm; 29-09-2020, 05:39 AM.
              It only took me 3 years to reach 100 posts and become a senior member!

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              • #8
                I find no sense in wiring the Fan relay from a permanent supply, I would never do it and would leave it the way you have it working.

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                • #9
                  Originally posted by 250ptm View Post
                  Here’s my understanding of how the whole thing works.

                  Honda engines normal operating range is around 88C 190C not the 165/175 of yester year. Also in their infinite wisdom Honda called both these components an ECT, the only difference: one is a switch the other a sensor.

                  The ECT (Engine Coolant Temp Sensor) (a 2 pin connector) is located under the distributor, alongside the single pin connector for the temperature gauge. The 2 pin (ECT sensor) is used by the ECU on pin D13 which produces a produces a 5v reference signal to this sensor. The resistance in the sensor changes with temperature which changes the reference signal of the ECU. That changes the fuelling/timing MAP in the ECU. If this part fails it will throw a Fault Code 6. (six rapid blinks of the Check engine light).

                  The other ECT (Engine coolant temp SWITCH) (also a 2 pin connector) is located on the Thermostat housing. It does not throw any fault codes if it fails. It trips between 91C & 95C (196-203F). That action grounds the coil of the fan relay. It also provides a signal to A12 of the ECU that the fan is running. The ECU is supposed to raise the RPM slightly to compensate for the current draw. Once the coolant temp drops by around 10F, it stops the fan as the ECT switch opens again.

                  James wiring diagram uses a permanent power source which should continue to run the fan (once the switch is closed) even with the ignition switch off. Unlike HONDA, which wires the coil side of the relay through the ignition switch, so it only operates when the ignition is on and the ECT switch is closed.
                  Thanks 250PTM, this is also my understanding of how this works, just took me a while to get my head round it, just to make it even more complicated there also also a further temperature sender in the same location which gives a signal to your temperature gauge in your dash.
                  Last edited by Dopeshow; 01-10-2020, 10:47 AM.

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                  • #10
                    Originally posted by keitht View Post
                    I find no sense in wiring the Fan relay from a permanent supply, I would never do it and would leave it the way you have it working.
                    My guess is to bring it up to modern standards. All modern cars i have owned (I think) have fans that carry on running one the ignition is turned off.Obviously because it is earth switched the fan will turn off as soon as it reaches the lower threshold. I was thinking it would help my stop melting my carbon fibre bonnet.

                    I take it you have wired your fan relay to a switched feed ??

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                    • #11
                      Originally posted by Dopeshow View Post

                      My guess is to bring it up to modern standards. All modern cars i have owned (I think) have fans that carry on running one the ignition is turned off.Obviously because it is earth switched the fan will turn off as soon as it reaches the lower threshold. I was thinking it would help my stop melting my carbon fibre bonnet.

                      I take it you have wired your fan relay to a switched feed ??
                      All my modern cars are the same but it still makes no sense, Once the engine is switched off there is no coolant circulation so all it is doing is moving the heat aware from the radiator which will naturally diminish anyway, There may be further cooling depending on fan position but it is only designed for radiator air movement.

                      The really concerning bit is the only thing stopping the fan from running is a rubbish little temperature switch, if that fails the fan will run until the battery is flat. My fan is ECU controlled but I have assessed all power circuits and have the bare minimum on a permanent supply, I also use a wireless battery disconnect.

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                      • #12
                        Originally posted by keitht View Post

                        All my modern cars are the same but it still makes no sense, Once the engine is switched off there is no coolant circulation so all it is doing is moving the heat aware from the radiator which will naturally diminish anyway, There may be further cooling depending on fan position but it is only designed for radiator air movement.

                        The really concerning bit is the only thing stopping the fan from running is a rubbish little temperature switch, if that fails the fan will run until the battery is flat. My fan is ECU controlled but I have assessed all power circuits and have the bare minimum on a permanent supply, I also use a wireless battery disconnect.
                        Good point keith. I didn't really think about that fact there is no coolant circulation.

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                        • #13
                          But it does pull cooler air (slightly) thriugh the rad and across the front of the engine. And any coolant in the rad will cool down and pull heat from the system reducing the risk of any pressure building in the system no?

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                          • #14
                            Originally posted by Underhauled View Post
                            But it does pull cooler air (slightly) thriugh the rad and across the front of the engine. And any coolant in the rad will cool down and pull heat from the system reducing the risk of any pressure building in the system no?
                            It does move some air over the engine but isn't designed for this purpose and is application dependent, Once the engine is switched off the coolant pressure and temperature will naturally diminish without any assistance.

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                            • #15
                              IMHO the reason car manufacturers make the radiator fans come on after the engine stops is because they are concerned about the effect of Heat Soak.

                              Am Engine block and cylinder head retain heat for far longer (due to their thermal mass) and can actually raise the coolant temp to the trip point of the sensor even after the engine has stopped.

                              Also there is the question as to whether the aluminium cylinder heads could potentially warp due to this continually repeated heat cycle is another consideration.

                              As I said in an earlier post Honda did not wire in the ECT to a live feed, (at least on earlier models). I’m guessing they did not see a problem at that time.
                              If there is a concern about having the fan run until it drains the battery, then you could fit a 5 minute time delay relay, which is basically what the latest fan controllers are.
                              It only took me 3 years to reach 100 posts and become a senior member!

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