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Old 09-24-2014, 04:24 AM   #1
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Engine compartment fan

Hello guys,
wondering if anyone of you have done or thought of that.
I'd like to place a switch to manually power the fan in the engine compartment.
This way I could better control and decrease the engine temp while in traffic and/or hot weather.
Any schematics?
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Old 09-24-2014, 09:11 AM   #2
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As soon as you disconnect the engine bay fan from the wiring harness, the car will start throwing codes as the DME thinks the fan has failed.
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Old 09-24-2014, 12:04 PM   #3
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If you find the relay (probably next to the other fan relays near drivers left foot), you can just wire a switch in parallel to the ECU signal wire. This way, the ecu will control the compartment fan as normal, and if you want to turn the fan on manually, you can.
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Old 09-24-2014, 01:09 PM   #4
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If you find the relay (probably next to the other fan relays near drivers left foot), you can just wire a switch in parallel to the ECU signal wire. This way, the ecu will control the compartment fan as normal, and if you want to turn the fan on manually, you can.
And the DME will see the fan running when it should not be and still code.....

They did not make this easy.
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Old 09-24-2014, 01:16 PM   #5
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Well, if that's true, which would be odd that they are wasting CPU time to check for a fan to be on that they did not turn on (avoiding proper coding technique discussion), then you could route your own power to the fan (annoying) and a few diodes later then fan would be under your control without letting the ECU know about it.

Then again, that's all probably a huge waste of time and you should rather implement an engine misting feature which lightly mists the engine to shed more heat
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Old 09-24-2014, 02:31 PM   #6
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Well, if that's true, which would be odd that they are wasting CPU time to check for a fan to be on that they did not turn on (avoiding proper coding technique discussion), then you could route your own power to the fan (annoying) and a few diodes later then fan would be under your control without letting the ECU know about it.

Then again, that's all probably a huge waste of time and you should rather implement an engine misting feature which lightly mists the engine to shed more heat
Unfortunately, the DME controls both the coolant fans and the engine bay fan, which is why they are so hard to alter the on/off temperatures. But because they are controlled this way, a Porsche diagnostic tool can test and even activate them at a keystroke, which makes trouble shooting a bit easier.
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Old 09-24-2014, 02:32 PM   #7
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Would there not be a way to change the temp threshold that activates the fan?

Just thinking out loud
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Old 09-24-2014, 03:39 PM   #8
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Well, no, and that is JFPs point. I agree it would be hard to try and manipulate anything the DME has info/control over.

BUT, why not tap the data for coolant temp (or get crazy and add your own temp probe [easy]) and then simply make yourself look like the DME (activate the signal pin of the relay that the DME normally controls). I have tested this for the coolant fans and it works as I described.

You use your own control logic to activate the existing (well built) circuit/relay, and have the added benefit of the DME still controlling the fans if its (the stock temp) conditions are met.

Whether or not you need to compliment the DMEs ability to control the fans is still something I'm not convinced of. My engine compartment fan comes on in traffic but it IS doing its job, and I have indicators to tell me when it is on and off, just to monitor. It isnt something I want to necessarily control however.

The only thing I DO want to add is a control loop to kick the high speed fans on if the low speed fans have been continuously on for x amount of time. Pushing it on the freeway, the low speed fans will stay on for loooong periods of time, which isnt bad, but if its a really hot day and the low fans have been on for a while, just kick on the high speed fans and get the temp down (this already happens if you are WOT for some amount of time, but 5th gear 4-5k on a 105 degree day, temps will stabilize around 214 or so, just above the low speed ON condition, leaving them on for quite a bit of time)

I guess this would actually help as ~214 for long periods isn't desirable, but isn't horrific either.

Last edited by epapp; 09-24-2014 at 03:42 PM.
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Old 09-24-2014, 04:42 PM   #9
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I don't really see the point except maybe if you want to upgrade the fans? Is this a common problem that the 987 runs too hot?
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Old 09-25-2014, 11:49 AM   #10
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Well, I'm speaking 986 temp numbers, and, no, I don't think there is a consensus that it runs too hot.

Its just for my style of driving, I notice the temp can equalize on the high side under very certain conditions, so to combat that, I can easily control them myself, but it easily appears to everybody else as useless since the car was designed with a temperature control system that should work.

The engine compartment fan is interesting because in traffic during 105 degree days, the heatsoak in the engine bay is probably extreme, hence the need for the fan in the first place.

Something thats bad that I've noticed is that the engine bay sensor is very close to the fresh air that the bay fan pushes in. It seems like to adequately lower the temp in the bay, the sensor should be in a place thats further away from the cooler air, to ensure the whole compartment is cooled down.
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Old 09-28-2014, 01:51 PM   #11
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Just turn on the aircon. The coolant fans automatically go to max.
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Old 09-28-2014, 03:13 PM   #12
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If you can solve the DME problem...doubt you can as JFP pointed out....the switch you have shown would not work. It is a toggle switch that is OFF in the middle position-- HOT on one side(push upper side) and HOT on the other side(push lower side) it reverses polarity from the top of the switch to the bottom. If you use this kind of switch it only needs an OFF/ON function not the pole switching capability that this switch has. Hope this helps.
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Old 09-29-2014, 12:01 AM   #13
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The coolant fans don't always go to max with AC on.

Only if the low speed fans have been on already and the coolant is around 212F will the fans go to high speed with ac turned on.

Plus, who uses AC in a porsche? :P
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Old 09-29-2014, 12:37 AM   #14
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You guys do realise you are talking about two different "fans" - the 2 x cooling / AC fans mounted at the front of the car, and the engine compartment cooling fan mounted just inboard of the R/H side air vent.
The OP first asked about controlling the engine compartment fan, which in my experience only operates for a few minutes in heavy traffic then quickly stops when you get underway and get air circulating around the engine. Its only a small fan with a +/- 100mm blades which really can't do much (apart from making a loud noise) to cool the compartment in stop go traffic or get rid of heat soak after the engine has been restarted after long periods in traffic.
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Old 09-29-2014, 07:39 AM   #15
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I saw replacement engine compartment fans some where that had 2X the number of blades. I can't seem to find them again, but that seems like it should help. I recently wrapped my headers this seems to help my engine temp while standing in traffic.
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Old 09-30-2014, 03:21 PM   #16
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Yes we are simultaneously talking about cooling fans and engine compartment fans
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Old 10-03-2014, 09:38 PM   #17
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Originally Posted by notech View Post
Hello guys,
wondering if anyone of you have done or thought of that.
I'd like to place a switch to manually power the fan in the engine compartment.
This way I could better control and decrease the engine temp while in traffic and/or hot weather.
Any schematics?
I think the easiest solution is to move the temperature sensors closer to the engine. Which will give the control unit a accurate engine temp reading and would run longer till the engine area cools. This way the control unit will monitor the temp for you and you wouldn't have be manual regulating the temp. Letting you enjoy the ride instead of being distracted about the temp of you engine.
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Old 10-31-2014, 02:52 PM   #18
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I saw replacement engine compartment fans some where that had 2X the number of blades. I can't seem to find them again, but that seems like it should help. I recently wrapped my headers this seems to help my engine temp while standing in traffic.
Going by the radiated heat and metal contraction noises after driving. I have found that a bypass exhaust helps to reduce temperatures in the engine compartment.....this is soley based on impression...no data

My theory is that less exhaust gas volume spends its time bouncing around the huge muffler imparting heat to muffler which in turn radiates less heat to the surrounding engine compartment, reducing ultimate temperature in there. The bypass tubes shoot the gases straight out.

I have plugged the bypass tubes and felt increased tempertures along with much more cooling chatter from the exhaust components.

My muffler is ceramic coated as well so the heat stays in the exhaust gases more than radiating out

One also has to consider the
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Old 10-31-2014, 03:02 PM   #19
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How often do others engine fans come on, I've noticed mine do it in traffic and sometimes when I park before I shut the car off, curious if my front two fans are up to snuff with the engine fan comming on too much in my opinion, unless that's normal of course.
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Old 11-03-2014, 12:21 PM   #20
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There's a temp sensor for the engine bay fan, I think it sits in the plastic intake manifold on the pass. side (at least on 2.5L cars). If you hit it with a hairdryer it'll kick the fan on.

Maybe find out what the signal/resistance is for the activation temp and replace the sensor. Fan should come on with ignition. Maybe??
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