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Discussion Starter #1
Hi all,

I wanted to install a fan switch in my 105 GTV 2000 for my electric radiator fan. I could install a switch in the bottom of the radiator or rather than drain the system of coolant I wondered if an easier solution might be to use a fan switch from a S4 Spider 1990-93 and fit this into the top of the cylinder head behind number 4 spark plug.

My question is: does anyone know the ON/OFF temperatures for this S4 Spider 90-93 switch and what are the pros and cons of placing the switch in this locatiion versus in the bottom of the radiator?

Many thanks for your help.
 

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But Mad North-Northwest
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Well, the S4 fan switch is on the outlet of the radiator, which is the cool side. So the temperatures for it (I think it's 75-85C) wouldn't really be relevant to the coolant temps in the head, which would be a lot warmer: **** thing would have your fan on all the time at normal running temps.

Basically the point of the fan switch is to only turn the fan on when the radiator isn't removing enough heat from the coolant (i.e., radiator outlet temps rise) as that's the only time the fan will make a difference. That's why it's typically on the radiator outlet.

Personally I'd do the job once and right, myself. Draining the system of coolant and refilling is pretty trivial.
 

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Another option is to use an adjustable bulb and capillary type switch. The bulb clips to the rear of the radiator and you adjust the switch so that it turns on when the radiator is at the temperature of your choice. I have been using one for several years without problems. I used to use the type that screw into the bottom radiator tank but The ones that I had were unreliable. Both of them failed.
 

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A good place to put a fan switch is where the temperature probe normally goes. ie in the inlet manifold just below the coolant air bleed screw. Then you can fit a coolant temp probe where the screw was. Only issue is that the thread here is smaller than that of the OEM probe. Solutions are to buy a probe with right thread or, as I found simple to do, reduce the thread diam on the stock probe (there was plenty of metal).
Cheers,
PB
 

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Premium Member
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Discussion Starter #6 (Edited)
Now that is a nifty solution!! Thank you both for your suggestions. It certainly is an easier option than having to drian the system, pull the radiator, and solder in a sensor in the bottom of the radiator. The trick now of course is finding a right temperature switch (ON 85 OFF 80) with a M14x1.5 thread. Any suggestions???

I do think that one benefit of the temp fan switch in the bottom of the radiator might be that it remains active ON when the coolant level is getting very low. Would a temp fan switch installed in the inlet manifold (as described above) work if the coolant level is v.low??? Im not sure?

Last, I seem to get occasional reports that these fan switches are rather unreliable.
 

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G'day,
Can't help with a switch number as I used a one which fitted to the temp probe thread. More importantly, you will notice that the switch is in the cooling system on the engine side of the thermostat in both of the suggested fixes. When I tried initially to fit a 90/80 deg C switch I found that the fan would switch on fine, but would not switch off because as the system cooled due to the fan cutting in, the thermostat would close at about 83 deg and the temp at the switch would then remain above 80!

No problem once I fitted a 100/90 deg switch. In practice the fan only turns on in hard competition ( my GTV is a tarmac rally car) or in very high ambient conditions (36+).

This is the ideal place for a switch because it is sensing the actual cylinder head coolant temp, which is what we are trying to control. If we place the sensor at the bottom of the radiator it may never get to switch-on temp, even if the coolant is boiling at the head at 105 deg or so!

It is true that if the coolant level falls below the inlet manifold level the switch and the temp probe may give erroneous low readings. but it would have registered sky high before this! A switch at the bottom of the radiator would not save the day and will not operate correctly under normal conditions.
 

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Folks, there is a very good reason most auto manufacturers, Alfa included, place their cooling fan temp. switches in the bottom of the radiator. That location gives a more useful indication of the effectiveness of your entire cooling system. Sure, you can find a switch in just about any temperature range you want for whatever location- hey, put it in the tailpipe, but it is not going to present a true picture of what's going on in your cooling system, which is after all the reason for the temp. gauge on your dash.
I would argue that the coolant temp. coming out of the cyl. head is not as relevant as what temp. it is at the point where the radiator has done it's intended work and is passing back into the block, i.e. the bottom tank. Coolant leaving the head is ALWAYS the hottest point in the system, and if it appears high you still don't know what's at fault- it could be a blocked radiator, crimped hose, or myriad other things. If there is a problem in the cyl. head such as leaking head gasket, steam pockets, etc. it WILL show up on your gauge too, as will any other problem in the cooling system.
If you look at a diagram of how the coolant is processed in a 105 series system you will see the sensor/switch in the bottom tank is ideally placed to monitor the health, or not, of the entire system. You may get a more instantaneous spot reading of one spot in the system w/ a switch at the outlet of the head, but I don't see how that is as useful as an overall reading. I CAN tell you what you'll get if you develop a leak and your switch is located at a high point in the system, no longer immersed in coolant, a potentially disastrous false reading and all the problems that can arise from that.
I can relate the example of a leaking bypass hose which lowered the coolant level bellow the high-mounted gauge sender which> overheating,> warped cyl. head,> money flying from wallet,> "honest guys, the needle never even registered hot!" falling on deaf ears.
I definitely remember the words of the guy at the machine shop specializing in cyl. head rebuilding and repair: "yeah, Ford really had a better idea when they put the sender on the thermostat neck...and those goofy bypass hoses- I might be out of business if they hadn't done that." That was the late 60's- or early 70's. They apparently learned the lesson from what I have seen of their current practices.
It IS your car and you should do what you want, just don't fool yourself about which is potentially more work.
 

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Fans!!!!

The point of either an electric or mechanical fan is to move enough air to cool the rad at slow speeds.

According to Shankle the mechanical fan consumes 7 HP at 6000.

Besides that the old fan on the 101 Alfas made a lot of noise.

I had two 9-inch pusher fans on my former Spider. These had the flat "scimitar" blades that made some noise. On a hot day and at a steady 50 mph these were blocking the flow such that the temp went up and turned the fans on. Redundant.

Put two 5.2-inch Spal "pullers" with paddle blades, which present less frontal area than the "scimitar" blades. Good rad and they worked well.
Paddle blades are quieter than the scimitars.

The rad for the Super was no longer efficient, so it has been re-cored with some 15% greater cooling capacity.

It is interesting that the lower front valence of the Super shrouds about 4 inches of the bottom of the rad core. I'm just finishing wiring up three of these small "pushers" at the bottom of the rad. Two are on thermostat and the third is on a switch under the dash. Sort of a fail safe. Thermostat is in the lower tank.

I'll add that this setup won't be blocking natural air flow and will be moving air through the the part of the rad that is blocked by the valence.
 

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Following Capp's post, would an insert into the bottom hose be a good place? Some suppliers offer a gland which enables you to feed the capillary under the hose, into the flow.
 

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Piper- from what I have seen and heard from those who have used the capillary bulb type of sensor placed in a hose, they do work satisfactorily. I have seen them fitted in top and bottom hoses, presumably according to whether the radiator is fed from top or bottom. Even the configuration where the bulb is wedged into the cooling fins of the rad. seems to work fine, but I cannot imagine that to be the best long-term solution.
There are other less invasive strategies if you don't want to cut into your radiator such as sourcing one of the 90's Saab in- hose sensors. There is extensive past discussion of this topic here on AlfaBB if you will spend a little time with the topic search feature including parts suppliers, part nos., etc. Try: radiator fan, fan switch, electric fan, fan control.....
Remember, you will want to wire the control of the fan through a fused relay AND ideally have a way to control it manually from the driver's position also (an override) for all traffic and temp. situations.
 
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