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PostPosted: Tue Nov 30, 2010 7:20 pm 
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Give Ash some flowers Nick .
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Joined: Wed Aug 09, 2006 1:22 pm
Posts: 10162
Location: Toowoomba Region, QLD
How to fit and wire a Thermo Fan to your Mini

For this you will need:

• Various connectors
• Wiring (min 20amp) of your choice of colour (length depends on where it runs)
• Thermatic switch to automatically turn the fan on and off when the car is hot
• A thermo fan (I used a 10” in this how to)
• Relay
• Fuse
• Toggle switch (optional)
• Soldering iron
• Solder
• Heat shrink
• Sheet metal
• Cutting disks / sheet metal shears etc
• Sandpaper
• Sikaflex
• A 1.2m length of rubber 32mm wide and probably 3 – 4mm thick
• Various spanners / sockets / screwdrivers
• Plus miscellaneous things I have probably forgotten

Method: PART 1: PREPARATION

1) Order all / buy all of the bits you need. You can add a LED light so you know when it’s running (you probably won’t hear it run over the sound of the engine when cruising). It is up to you.

2) PLAN! Before you start, think about where you are going to put things as this will determine how much wiring you will require.


3) This is the thermo switch I bought. It is adjustable so you can dial it in to whatever temperature you want it to switch on.

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4) We want to make something that looks like this (this is the one that is on my car – been in action about 18 months now – it is a 9”)

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5) This is the little toggle switch I bought from Jaycar – ST0300. It is a SPDT (single pole, double throw).

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6) To make it easier for you I have attached a sketch of how big the hole is within the guard (note I did not cut any of the grille bars for this, no holes were drilled etc). I then just cut the pieces of sheet metal to suit the size of the thermo fan I had bought. I also worked out the size of the fuse I would need to supply.

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For electrical things in cars there are two main equations that you will need to know:

a) V=IR (Voltage = Current (Amps) x Resistance (Ω - Ohms))
b) And W=VI (Watts = Voltage x Current (Amps))

You can rearrange these equations to suit what you are trying to find e.g. if you had 60W high beam light bulbs this would work out to: 60W/12V = 5A.

For this example I had to wait until I had the thermo fan in my possession to measure the resistance. Use your multimeter for this. Just stick the two probes on the ends of the wiring of the fan and your meter will stabilise on a number (make sure you have the meter on the right setting). This is the number you use in your equation.

For my purpose this is 3Ω of resistance so:
V=IR
12/3 = 4A (motor will draw 4 amps)

I never run the same fuse as what the item will draw. I usually build in a 20% redundancy so 4 x 1.2 = 4.8Amps. You would then pick the next size fuse up from this that is commonly available (5amps). This should be enough for this fan (note the instructions said to run a 20A fuse). I didn’t have any 5 or 7.5A fuses lying around so I used a 10A fuse.

7) Once you have that sorted you need to think about your wiring. FOR THE LOVE OF GOD DO NOT WIRE THIS STRAIGHT THROUGH THE IGNTION SWITCH. You need a RELAY for this. I found a really good relay at Jaycar (SY4076). It already has a blade fuse built in! I also use a Horn Relay Base (SY4069) to make it a neater install. I just swapped the 15A fuse the relay comes with for a 10A.

I have attached the wiring diagram that I did. You can change yours to incorporate different things if you want. I have drawn the fuse separate to the relay as not everyone will buy a relay with a fuse already part of it.

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If you have no idea what a relay does read this link: http://www.mp3car.com/vbulletin/faq-emporium/117895-faq-relays-how-they-work-how-wire-up.html

8) After you have that sorted break out the solder & heat shrink and solder up your switch connections etc

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9) You may find that you have a weird connector on your thermo fan. I just pulled the outer casing off:

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Which left me with:

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I don’t trust crimped connections so I also put some solder onto these connections as well.

10) Start thinking about cutting some sheet metal up for use as a shroud. If you don’t fit a shroud your fan will not be as effective and you will wonder why you went to the trouble of fitting it (unless it is pressed right up against the radiator). I cut out the bits and then bonded the metal to the fan with Sikaflex. Once it has dried you can sand it back and paint it.

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PART 2: RADIATOR REMOVAL

11) Make sure the car is cold. Start by removing the grille and draining the coolant ensuring that >50% of the coolant misses your carefully laid out tub and ends up in a big puddle on the floor.

To do this put a long flat head screw driver down behind the radiator to remove the bottom hose at the radiator end. Undo this hose clamp enough to be able to slide the hose off with your hand – this will release the fluid onto the floor.

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^^Note where screwdriver is pointing – hopefully your hose clamp is facing the correct way (as shown in pic)

12) Then fit up where you are going to be placing the thermo switch (it has to be within reach of one of the radiator hoses.

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The probe from the switch needs to be able to fit in a radiator hose:

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13) Next put some chocks under the rear wheels and put the car up on axle stands

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14) Undo the passenger side engine mount bolts

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15) Next grab a lump of hardwood to spread the load of the floor jack on the sump. NEVER jack a mini from the sump with an unprotected jack. Use something to spread the load over a greater surface area.

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16) Jack the sump slightly so you have the following effect – the engine mount will lift slightly away from the subframe. This is all the extra space you need:

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^^Note for later where the spanner is in the photo

17) Remove the top hose, undo the two ½” nuts and two 9/16” bolts holding the top bracket in place that secures the top of the radiator.

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You then remove the two ½” bolts holding the bottom of the radiator in the car (they almost face up and down straight under the radiator, above the engine mount). A stubby ratchet spanner is excellent for this job (remember that photo that I told you to remember the position of the spanner????)

18) Remove the radiator from the car (sorry the picture is blurry)

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^The radiator just needs to be on the right angle to come out. Sometimes it helps to spin the blades of the fan with your hand to help it come out. It helps if you tip the top of the radiator forward, I had it like this so I could take a photo with my other hand.

All done:

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I have shamelessly pinched that method of radiator removal from Matt Read "The Mini Man".

PART 3: THERMATIC FAN INSTALLATION

19) Next I fitted a new rubber surround around the radiator. These never last long due to the heat cycling of the engine. I bought 1.2m worth of 4mm thick x 32mm wide rubber from Clark Rubber for a smidgen under $10. I then stuck it together with some super glue so it was 1.12m around (i.e. overlapped it 8cm). You can see the join at the front in the photo:

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20) Next is drilling some holes in your shroud and attach it to the car. I used zip ties for this one because I didn’t want to drill / cut the body. The fan is just placed over the top of grille bars and then I used a little Sikaflex to seal the holes between the body and the fan / shroud.

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21) This is what it looks like all fitted up from the wheel side – NOTE: I put the wiring from the fan motor facing down so it does not collect moisture.

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22) I then ran the wiring through the front panel

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23) For an earth I used the bolt that holds the oil cooler in

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24) This is my earth. You will need to think about what kind of connectors you will need as I won’t be showing you everything. As with all of my connections on this car they are all soldered with heat shrink.

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25) After all that is done put the radiator back in the car. Installation is the reverse of removal.

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26) Run all of your wiring as per the wiring diagram provided. Remember to keep the wiring neat. Don’t have wires running across the engine bay!

27) All fitted up and ready to go. I used the “horn relay base” so that all the connections could be easily unplugged to remove the radiator and then plugged back in in the correct positions.

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I mounted the thermo switch just above the relay.
28) I got power for the fan from the starter solenoid (battery side).

29) I got power for the interior toggle switch / thermo switch from the UNSWITCHED side of the fuse box. I use the unswitched side of the fuse box so that the fan will continue to run after the car is switched off. This helps to prevent heat soak as the hot water will rise to the top of the engine block and the cool water will fall to the bottom of the radiator etc.

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30) Reassemble everything; fill with water (just to test for leaks where the probe goes into the top or bottom hose – depending on where you positioned everything). If it leaks (I bet it will) just put some kind of silastic stuff there to seal it up and re-slip the radiator hose back over. Once you are confident you have no leaks pour in some actual coolant and start the car and wait for it to warm up.

31) You don’t want the thermo fan coming on too much. This is why the switch has the adjustable knob! The fan should really only run for 30 – 60 seconds at a time (bit more in hot weather). Keep turning the knob clockwise to increase the temperature until this happens. This is intended to aide low speed cooling (i.e. stopped at the lights) as it will not help your car at speed (it shouldn’t operate while you are moving along). The interior toggle switch used in this version if you wish to operate the thermo fan without having the temperature high enough to kick the fan in (i.e. in between hill climb runs etc).

The radiator should be a firm fit next to the rubber surround. This is to ensure the air passes through the radiator, not around it. When the motor is switched off and the fan going, you should be able to feel the fan pulling air through the radiator from the engine side.

When the fan is installed ensure that the fan acts with the engine driven fan, not against it i.e. air flows in through the grille of the car, past the engine, through the mechanical fan, through the radiator and into the wheel well.

You may want to also think about some wet weather protection. I ran some sikaflex around the outside of the temp switch.

32) It should be set and forget. All up this cost about $130 - $140. Everything here was brand new / stuff I had lying around. It would set you back a bit more if you had to buy EVERYTHING. Enjoy!

_________________
"In two years time your car will be like a lady's clothes, out of date, my car will still be in fashion when I am dead" - Sir Alec speaking to Pininfarina


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