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Engine coolant temperature & fan activation temps (Updat

L

Locosaki

Nurburgring
Joined
3 Jul 2016
Messages
409
Having read through various threads on engine temp etc I've been monitoring my own.

In town I've been steadily over 100 so thought I would start by cleaning rads as there was a lot of leaves built up in there, the engine fans appear to come on around 105 and cool back to approx 100.

Coolant level was also on the minimum so this still requires topping up.

The fan on the boot lid is not working, I removed air temp sensor from the manifold but still no engine fan, I checked the fuse which was fine then went for the relay this is where I got confused.

The relay 4 numbers, 30,85,86 & 87

No. 30 is live via the fuse and 87 is switched live to power the fan,no. 85 should earth to ground and 86 I assume should be the trigger that energises the coil. Problem being, I have 12v down both 85 & 86 and this is why I think the fan in boot lid is not firing up.

I bridged power at the relay and the fan worked.

I checked resistance on the sensor and that's good too

Has anyone got any knowledge on this at all, I presume the engine fan not coming to life will not be helping my temps
 
Magic thanks for the input I'll have a look over and get back to you.

The car is a coupe, MY 99 Carrera 4
 
Front fans (rads) kick in @ 105 deg C (coolant)
Engine bay fan kicks in @ 85 dec C (air)
 
So would 105 be low speed fans if so what temp would high speed activate
 
105 dec C is the high speed fan (I was assuming you had CC on all the time, ie you had the low speed fans already continuous - it is unlikely, and ultimately more damaging, to switch off the AC circuit)

IF you did turn off the CC, as in no forced ventilation (or AC was off, as in no snowflake), the low speed kicks in at circa 97 deg C

The high speed fan will also be operated if the refrigerant hits 16 bar pressure (if it hits circa 32 bar, the DME will take the compressor off-line).
 
If the fans aren't on low speed all the time with air con on then your resistors might be duff.

Replace for £12 rather than pay Porsche tax:

0.5R 100W (RS code 188-071) resistor
http://uk.rs-online.com/web/p/panel-mount-fixed-resistors/0188071/

Green = Low speed fan supply
White = High speed fan supply
Green/White = Output to fan motor

Solder the White and Green/White wires to one side of the resistor solder the Green wire to the OTHER end of the resistor.

You'll need a decent wattage soldering iron and some heat shrink.

From http://rennlist.com/forums/996-forum/737811-ballast-resistor-replacement-2.html
 
I've been out an rechecked supplies to relay for the engine lid fan, the diagrams were much appreciated.

Terminal 30 has power, terminal 86 is powering up with ignition on, terminal 85 back from the ecu is giving 12volt which were assuming is the problem.

I traced the yellow wire with red trace back to ecu and done a continuity check and there is no issues there.

Could this be a fault with the ecu, I noticed when I removed the ecu that it has been to the ecu doctor for something before I bought the car.

I just checked to ensure both fans come on with I hit the snowflake on my CC, they both work away fine.
 
You have pretty much covered it , it should be an earth switch on the dme wire and you have 12 v ..

Only thing to check is its not shorting to + ..

Youll need to take the connection T85 out of the dme plug ( just that wire ) then check for 12 v .. if nothing then you have pretty much proved its a dme fault.

It is kinda possible that you are reading a back feed voltage untill it switches an earth , i kinda doubt this but im trying to cover everything and it has been modified .... if this is so then a continuity check on the temp sensor wires and proveing the sensor is ok needs to be done.

Standard checks then apply .. good feeds / earths to the dme .

I would normally suggest a dme reflash at this point but you mentioned ecu doctor so at this point i cant say that a standard flash would help .. it depends on if its a flash upgrade / map or a chip insert .. the later might die if reflashed.


Front fans and rear fan are seperate systems.

Btw .. excellent work .. if your not in the trade then you should be :)
 
Thanks again Dermot,

I've been about cars for years and always do what I can myself, I'm a heating engineer to trade so know my way about a multi meter etc, thanks for the kind words.

I shall pull the wire from the DME tomorrow and check for a short, the sensor in the engine bay is fine, the resistance is dropping as the sensor heats up, basically an NTC sensor similar to what I see on boilers.

The next move as you say is check the wiring from the sensor back for continuity.
 
Aghh that makes sense now .. but how you can switch between a/c and d/c is beyond me !

I just cant get my head around a/c .. too many years on d/c i guess lol.

Just a thought though .. when i do a continuity check i also check for short to earth and short to + .. its kinda automatic .. so just check that while your at it , eliminates just about everything then .
 
Excellent thanks for the tip. I'm early finish tomorrow so I'll report my findings back.

Thanks again.
 
I've been back out and removed the wire from the DME, this wire is still getting a 12v feed some how, I'm wondering if it is a back feed through the relay coil now, when ignition is off no 12v.

I earthed the yellow/red wire against the car and it brought the fan on.

No matter what I try at the wires at the NTC sensor I cannot get this fan on, 2 wires in question are brown/pink this wire is connected to 4 other sensors and the blue pink which goes back to the DME from the sensor.

Is there a resistance I can test for across these 2 wires or a short I can look for.

Thanks
 
Re: Engine coolant temperature & fan activation temps

Locosaki said:
Having read through various threads on engine temp etc I've been monitoring my own.

In town I've been steadily over 100 so thought I would start by cleaning rads as there was a lot of leaves built up in there, the engine fans appear to come on around 105 and cool back to approx 100.

Coolant level was also on the minimum so this still requires topping up.

The fan on the boot lid is not working, I removed air temp sensor from the manifold but still no engine fan, I checked the fuse which was fine then went for the relay this is where I got confused.

The relay 4 numbers, 30,85,86 & 87

No. 30 is live via the fuse and 87 is switched live to power the fan,no. 85 should earth to ground and 86 I assume should be the trigger that energises the coil. Problem being, I have 12v down both 85 & 86 and this is why I think the fan in boot lid is not firing up.

I bridged power at the relay and the fan worked.

I checked resistance on the sensor and that's good too

Has anyone got any knowledge on this at all, I presume the engine fan not coming to life will not be helping my temps
Click to expand...

Are those temps normal? Mine usually sits on 80 but in traffic may go to 85 tops.
 
Re: Engine coolant temperature & fan activation temps

stevepen said:
Are those temps normal? Mine usually sits on 80 but in traffic may go to 85 tops.
Click to expand...


+1
 
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