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Old 01-24-2016, 04:46 PM   #1
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Engine Compartment Fan Manual Switch

Here is how to install a switch that will allow manual control of the engine compartment fan.

This is not for the radiator fans at the front of the car but rather the fan that cools the engine compartment by drawing in air through the passenger side vent in the rear fender (engine intake is on drivers side, engine compartment fan is on the passenger side).

I wanted to manually control the fan at the race track on hot days to provide additional cooling to the engine and engine compartment after coming into the pits after a track session.

It is fairly easy to tap into the engine compartment fan relay. The difficulty in this job will come from deciding where to mount the switch and running the wires from the rear trunk to the switch location.

In the case of my Spec Boxster race car, I was fine with installing the switch in the rear relay tray. To switch the fan on at the track, I just open the rear trunk and hit the switch on or off.

Here is how the engine compartment fan works;

Engine Compartment Purge Fan
To reduce the temperature of the engine compartment, a fan actuated by the DME is installed behind the ventilation grille of the passenger side rear fender vent.

If the fan is active, fresh air is fed into the engine compartment. There is a temperature sensor mounted in the engine compartment to provide temperature input to the DME.

Standard Operation:
1. With engine running or ignition on:
If the engine temperature is higher than 102 C and the engine compartment temperature is higher than 60C, the engine compartment fan is switched on for 30 seconds by the DME control unit and the engine compartment is thus ventilated.
2. With the engine off and vehicle is stationary:
If the engine compartment temperature is higher than 60 C when the engine is switched off (ignition off) or if the engine stalls (engine speed: 0 rpm), the engine compartment fan is switched on for 20 mins.

Note: If the engine temperature has not dropped below 80.25C after the engine compartment fan has been running for 25 seconds, a fan fault is registered and the coolant level warning lamp is activated (flashes).

To install a manual control switch:

Open the rear trunk and locate the rear relay panel. It is tucked way, way, way up under the driver side fender. You will have to pull back the trunk carpet/lining and look inside the fender well to see it.


Remove the two screws holding the relay panel and slide it out towards the center of the trunk. It may take some pulling on each side to get the relay panel to slide out. Be careful not to break the plastic relay tray.



Continue to pull the relay tray from its sliders. Now the relay tray should be clearly in view.



The engine compartment fan is controlled by relay #8. This relay is a standard Type 53 used throughout the Boxster.



To test the engine compartment fan, simply jumper relay pins 30 and 87 as shown below. The engine compartment fan should turn on.



Remove the relay and install one pin tap at pin 30 and a pin tap at pin 87, bend over at 90 degrees so the blade will come out from the underside of the relay and re-install the relay. Here is an example of a pin tap on a fuse. They are easily modified for use on a relay.



Last attach two wires to the pin taps at the relay and then route the wires to the switch to activate or deactivate the engine compartment fan.

Alternatively, I could have figured out which pin is ground (30 or 87) and then you'd only need to run one wire from the relay (the non-ground pin) to the switch and the other wire could be grounded locally near the switch.

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Last edited by thstone; 01-24-2016 at 05:09 PM.
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Old 01-24-2016, 05:49 PM   #2
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Quick question, have you had an issues with manually triggering the fan causing the CEL to come on? You mentioned the possibility of a fault code.

Great job, and great post! I will be looking into this, my Boxster runs hotter than I would like in the summer.
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Old 01-24-2016, 07:27 PM   #3
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Nice.......... Tom!
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Old 01-25-2016, 05:38 AM   #4
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Never heard of pin taps. Who sells them?
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Old 01-25-2016, 06:35 AM   #5
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Never heard of pin taps. Who sells them?
Most auto parts stores stock them. Here are links to AutoZone and Amazon:

Dorman/Fuse and Accessories 85606 - Read Reviews on Dorman #85606

http://www.amazon.com/WirthCo-30001-Fuse-Tap-Fuses/dp/B000CQBNFI
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Last edited by thstone; 01-25-2016 at 06:37 AM.
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Old 10-27-2016, 11:29 AM   #6
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Why not tap into the harness wires with wiretaps?

Also, you mentioned this was only for cooling down engine bay AFTER the track session. Makes sense, but would there be a benefit in running it DURING the session to help cool airflow around the oil cooler and help keep oil temps down? How many CFMs is the fan?
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Old 10-27-2016, 11:58 AM   #7
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Quote:
Originally Posted by AZ986S View Post
Why not tap into the harness wires with wiretaps?

Also, you mentioned this was only for cooling down engine bay AFTER the track session. Makes sense, but would there be a benefit in running it DURING the session to help cool airflow around the oil cooler and help keep oil temps down? How many CFMs is the fan?
The oil cooler is cooled by engine coolant, not air flow. If you want to lower oil temps, use a larger cooler on a base car, or lower the coolant temperatures.
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Old 11-03-2016, 05:40 PM   #8
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Originally Posted by AZ986S View Post
Why not tap into the harness wires with wiretaps?
My solution simply adds a manual switch to command "On" the relay.

Using wiretaps and a switch to go direct to the fan would bypass the relay which is not a very good approach. Relays exist for a reason.

How To Use Relays and Why You Need Them
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Old 11-09-2017, 08:09 PM   #9
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Why not put in an adjustable thermostatically driven relay?

Any time you get 60C or more the fan goes on until it comes down to 60C.

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