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D2 - Engine Bay Everything under the bonnet

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  #21  
Old 18th September 2016, 12:14 AM
MikkiJayne MikkiJayne is offline
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This diagram may help explain how the logic works:



N39 is the resistor pack underneath the left side of the engine bay. V7 is the stock fan. F18 / F54 is the thermo-switch in the radiator.

Lets look at N39 first. This is how the three fan speeds are achieved. Put power to E1 and it has to go through two resistors before it gets to the fan, hence slow speed.
Power to E2 and it only goes through one resistor - middle speed.
Power to E3 and it goes directly to the fan - max speed.

Top left is relay J26. You can see this is switched from the F18 thermo-switch, so this comes on when the radiator outlet exceeds 87*, and switches on the fan at slow speed. Note also the connection to track 95 - this is the HVAC controller, allowing it to request the fan to come on, which afaik it does whenever the compressor is engaged.

Top middle is relay J101. This is switched from the F54 thermo-switch if the radiator outlet exceeds 93* and brings the fan on to medium speed. Note also the connection to track 45 - this is the AC condenser pressure switch. If the refrigerant pressure gets too high, ie not enough cooling air on the condenser, that will also switch the fan to medium speed.

Top right is relay J135. This is the last resort, and is switched from the instrument cluster in case water temperature cannot be controlled by the thermo-switch. This brings the fan on at maximum speed.

This is mine:



Vnew is my Spal fan which has replaced the viscous fan. The output from V26 (slow speed) is disconnected from the resistor pack and instead connected to my new fan. So, any time fan slow speed is requested (either by the thermo-switch or by the HVAC) the new fan comes on instead. Medium and maximum speed on the original fan still works as they should, the main difference being there are now two electric fans running instead of one plus the visco.

My fan is getting switched 12V from a relay, not via the resistor pack, so it always runs at full speed, however its power consumption is much less than that of the original fan which can pull ~40A on full speed.


Last edited by MikkiJayne; 18th September 2016 at 12:20 AM.
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  #22  
Old 18th September 2016, 06:54 AM
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Ameiseuk Ameiseuk is offline
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Nice write up, good explanation and it looks a good setup.
About to convert the Land Rover to an electric fan setup as the Daihatsu engine that's been dropped in to the engine bay doesn't allow for a mechanical fan.
That said the wiring is much, much simpler on a LR!
Engine bay now looks very empty without the 18" of cowling fitted to the back of the radiator
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  #23  
Old 18th September 2016, 08:28 AM
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Thanks for the explanation!
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  #24  
Old 7th July 2018, 09:04 PM
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Goran Goran is offline
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Hi MJ,
I bought the fan you recommended and a piece of nylon 6 sheet.
I was ready to do the conversion but then I had doubts if my AC fan is switching on correctly.
If engine temp is 100C on the Engine advanced measuring blocks, should the AC fan be kicking in at the low speed?
Mine does not start at all unless the AC is running and unless the engine temp is something like 110C on the cluster needle dial. Is this correct operation of the AC fan?

Also I tried the rolled up newspaper test on the viscous fan when engine temp was 100 but I couldn't slow it down or stop it so perhaps its working fine.
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  #25  
Old 7th July 2018, 09:12 PM
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Goran Goran is offline
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When I switched on the AC, the AC fan brought the temp down to 96C quite quickly.
So I'm thinking maybe my F18 and F54 thermo switch module is bad?
It seems unlikely that two separate relays J26 and J101 are both bad, although I guess anything is possible.

Last edited by Goran; 7th July 2018 at 09:15 PM.
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  #26  
Old 7th July 2018, 09:32 PM
MikkiJayne MikkiJayne is offline
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Yeah sounds like the thermoswitch in the rad has failed. You can test the it with a pair of pliers in the connector contacts, if you can get to it (bumper off), but with your aux heater you may have to put the front panel in service position to reach the switch.

Funny this thread popped up again - I've just drawn the fan mounting panel in CAD to send off for laser cutting in aluminium next week

I don't like the new fan logic though as there is insufficient airflow while stationary for the AC to work properly. I'm probably going to put a second speed controller in for the new fan instead so both fans have three different speeds, and switch the lowest speed off over 30mph so the fans aren't running constantly.

Last edited by MikkiJayne; 7th July 2018 at 09:35 PM.
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  #27  
Old 8th July 2018, 09:50 AM
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Goran Goran is offline
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Thanks Mikki you are a star!
I'm going to try getting to it with just the bumper off.
Let us know about the new speed controller new logic sounds good. Not that I use AC much anyway.

Is it normal for a working viscous fan to be unable to control engine temp when ambient is 30C?
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  #28  
Old 8th July 2018, 02:17 PM
MikkiJayne MikkiJayne is offline
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I would expect the electric fan to be needed as well in this weather, although the effectiveness of the viscous fan can be compromised by dirt in the fins which prevent it sensing the air temperature properly.
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  #29  
Old 8th July 2018, 04:14 PM
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Goran Goran is offline
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Thanks, good to know. Looks like my viscous fan is still working. I'm gonna have to fix this thermo switch. Unfortunately I left it too late I'm off on a Euro roadtrip on Friday I dpnt think the dealer can get it before then.
Its a good thing the ac fan still works I just have to make sure to keep the ac on when I'm in traffic.
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  #30  
Old 21st July 2018, 04:57 PM
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The_Laird The_Laird is offline
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My S8 has started to overheat on hot days, particularly in slow or stationary traffic. It usually runs bang on 90. Is the electric fan a likely culprit and will it show up on vag com?
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