anyone fitted a radiator fan switch?

[Dantes]

What a great melting/boiling pot of discussion on the wee switch. Can I ask for further guidance as I was just pondering on the idea of moding a light thats already on the dash and unneeded, to turn on when the fan stage 2 comes on from the thermo-switch (the automatic route)? That way I might see when the fan kicks in on a long climb (will try the Alps at a later stage). My manual bypass switch has a light, but thought if a light came on to tell me when the fan was on then that'd be puurrrfect. Any ideas? Using the relay connections? [My relay is: 89 96 41 12v 70A (251919505SHO)].

Or maybe even go the whole hog and add a resistor to get the light to show stage 1 and 2 (things I think of when admiring the olde girl with tea and cigarettes). I know all these things are maybe not needed, but with the family asleep in the back going up the hill I like to know whether to relax waving my hand through the passing air or lean forward stressfully looking at the temp guage. Long live Wanderlust.

[Doctor Foster]

Wow, what a response. Only just checked back on this.

I fitted the switch a while back now and so far it works a treat. Used it a couple of times in France when I noticed the temp gauge had crept up. Peace of mind switch really!

Good debate though

[Red Westie]

Whilst we are getting all technical lol....I thought I might add a few lesser know facts and the odd opinion.

Most of the reasoning behind the need for an overide have been based on climbing hills at low speed but hammering the revs and throttle.
So some more facts into the mix.....lol

Altitude effects the boiling point of water (coolant) most people know that water boils at 100 degrees C at sea level but did you realise that at around 2,100metres, I mention this particular height because I went over the St Gotthard Pass only last week so have recent experience. At 2,100 metres the barametric pressure drops which lowers the boiling point over 7 degrees centigrade.
Look at the link to see by just how much boiling point is effected:
http://missvickie.com/library/altitude.html" onclick="window.open(this.href);return false;

Now if we go back a few threads Simon wrote that for every pound pressure you put the coolant under (with a sealed pressized system) it raises the boiling point by about a degree (roughly). So with a normal pressure cap that works at around 15PSI that's a 15 degree increase in the boiling point of the coolant.
The pressure cap release is set by a spring/valve so remains constant against atmospheric pressure. so....
NOW lets minus the 7 degrees C and all of a sudden your pressurised coolant boiling point drops to below 108C at this particular height, add more altitude and that drops even lower!
Now all of a sudden allowing the needle past the LED (well over the 100C mark) the engine starts to get perilously close to the boiling point.
More facts
Coolant removes heat from components through conduction (the coolant passing close by the heat source and taking on the heat energy, then moving quickly through the system to the radiator where the heat is imparted through radiation to the air passing through the fins).
BUT: Liquids conduct heat well, vapour/gas does not! so if boiling starts localised hot spots occur leading to warping and even melting of components.
Yet more:
Most engines use two basic metals in their construction (iron and alluminium) these metals have quite different thermal expansion rates, so when the engine gets very hot it becomes difficult to keep seals and in particular the head gaskets, sound and intact.
On a different note
Oil temperature (in my experience) is very much down to engine work rate, so can be relatively low even with a boiling engine BUT where the engine is being hammered like this (3/4 to full throttle at low speeds with highish revs) it is also going to be fairly high, compounding the temperature issues, as one of the oils main functions is to cool the components as it lubricates.

Martin

[HarryMann]

Yes, exactly, absolute system pressure comes down with altitude..

BP decrease /increase with pressure for about 10 deg C below/above 100 C about 2.3 deg above, 2.7 below

Should expect about 130 C with a 15 psi cap?
Should lose about 4.6 psi at 3,000m (10,000 ft)
So BP still about 120 C ? All depending of course on sea level baro pressure

What happened to the Clarkson boys at extreme altitude int eh Atacamas was it? Starting problems mainly I seem to remember.

=========

Slight corerction..

Coolant removes heat from components through conduction (the coolant passing close by the heat source and taking on the heat energy, then moving quickly through the system to the radiator where the heat is imparted through radiation to the air passing through the fins).

This is also mainly conduction from water to ally/copper, ally/copper to air; radiation is a small component of the radiator's total heat rejection.

[Red Westie]

20% less oxygen up there too.....sure makes the engine a little weazy.

Martin

[Dantes]

Took my old XTZ750 over the mountains one year and the engine was misfiring until I returned below 1250 meters, and nobody wants to start playing with carburetion mixture screws when you are trying to get somewhere especially fully loaded with lugagge. Thank goodness for Diesels.

What I did in the end with my T3 was but a switch between the heavy red/white wire below/beside the relay where its got the heavy duty fuse and leading to point 86 of the relay number 5. This way the switch isn't connecting a heavy load and activates the fan stage 2 directly (very easy to do). Then carried an extra ground wire from the switch to activate the associated light. Additionally stuck an extra wire from the red/black on the by the thermo-switch to a seperate spare bulb on the dash that wasn't used and ran this to another ground wire to the ground crowns. Now whenever the fan comes on automatically I know about it with a powerful stage 2 switch to kick in whenever I know I'm about to tackle a brute of a climb. Works for me.

Cooling the oil would be an ideal way to tackle raising temperatures, but I'd imagine this would involve big money and not the price of a ickle switch (I actually used an extra Hazard light switch turned the other way round to activate the relay). Simples.

[Red Westie]

Yes, exactly, absolute system pressure comes down with altitude..

BP decrease /increase with pressure for about 10 deg C below/above 100 C about 2.3 deg above, 2.7 below

Should expect about 130 C with a 15 psi cap?
Should lose about 4.6 psi at 3,000m (10,000 ft)
So BP still about 120 C ? All depending of course on sea level baro pressure

Acording to a graph I've just looked at ...not as high as you might think......15PSI at sea level is a boiling point of 121 C

2nd stage on the fan kicks in at 103 C

Take off nearly 8 degrees at 2100 metres so thats 113 BP
Then that depends on the system being fully pressurized and the cap after 20 years plus, still holding back 15 PSI?
Just a 10 degree safety margin IF everyting is functioning correctlly and to NEW spec.

Interesting the more you go into it.
Martin

[HarryMann]

Yes Martin, thanks

so say 121C at +15psi (reviewing another source)

Ethylene Glycol Antifreeze BPs

Weight Percent EG (%) Boiling Point (deg F) Boiling Point (deg C)
0 212 100
10 215 102
20 215 102
30 220 104
40 220 104
50 225 107
60 230 110
70 240 116
80 255 124
90 285 140
100 387 197

so for 50/50 which we should be using then that's 7 Deg C (10 C if 60/40 strength, about the max one would use, frost protection max at 70% mix)

Say 121 + 7 = 128C at ISO +0 S/L (1013 mb)

At 2100m we lose 7 something degrees (for water), and if A-Freeze/Water mixes follow this same rule, we are...

Back to 121 C

Fan comes on at 103C (providing 18C margin)

On the other hand, the engine will be producing less maximum power, and the charge mass will be less, requiring less advance (in theory)
Also, the mixture will be a bit rich, on carburrettorred (yes, at least 10 spellings!) engines and maybe on some early injection engines.. this should cool the engine.

Let's conclude that the recommendations are:

* Ensure both fan stages are coming on, approx at the correct temps, before venturing far from home (or a manual switch achieves same).

* When venturing above 2,000 metres, your radcap should be a good one and not 25 years old; your cooling hoses & connectionsshould be in good condition and not about to rupture at 15 psi (1 bar) above ambient

* Also ensure your anti-freeze is fresh and at least 50/50... to gain the 7~10 Deg. C increase in BP (100% EGlycol AF doubles BP)

* High altitude sometimes implies difficult terrain, or restricted options... try not to overheat or lose your water up there, you might have to climb further before descending.

* Barometric s/l pressure affects BP of course, so if in Low Pressure (cylconic) weather system, situation is even worse

[Dantes]

Hi Epiphone,

This feels like an age ago now, but yes I had a spare bulb just below the clocks that was previously used to flash when indicating, but that seemed pointless to me as it flashed clearly on the dash . So I hijacked this bulb socket and instead ran a feed from the radiator. Now when the radiator is in stage 1 you can tell its on (as you can't always hear it whilst driving). So when I know I'm working the engine I can be reassured when the light comes on. It also comes on if I flick the button I installed for an immediate stage 2 operation. I like it, if you want to do something similar I will go out and remind myself what I did at the time. Happy cruising.

[Epiphone]

I've installed the 2nd stage fan switch tapping into the relay panel. Works fine.

I'm looking at 1st stage fan indicator/bulb. Surely I don't want to take a high current cable straight from the thermoswitch/fan to light a small bulb. So another relay is needed which triggers when the cable from come the thermoswitch to the fan becoms live = thermoswitch at 95, With the live for the blub coming from the x-bus. I took feeds of the cables coming out of the thermoswitch. I Also took my own earth from the cab too. Meaning 3 cables thought the firewall to the the relay.
I've done that but only tested it by tripping the relay.

Then if I want to be able to switch on the 1st stage, do I then need another relay for the switch from the cab. I can use same earth but then would need another cable through the firewall for the switch. I can tap into the high current live to then feed the fan. This would ensure both circuits are separate to ensure the continuing normal function of the thermoswitch and the bulb indicator, while only having low current feeds thought the firewall?

[jamesc76]

I have fitted a chicken switch for the rad fan to every car I have ever owned( ok still need to do the T4) I like to be incharge or my van and not leave it to chance, especially as I have a scooby engine and it can get rather warm in static traffic!

[Epiphone]

Just to update, when the 1st stage fan starts, via the thermo switch, my relay kicks in and ignites the bulb. So works perfectly.

Also when I flick my chicken switch, the bulb is lighting up also, aswell as the bulb on the chicken switch itself, so a nice little addition too.

Haven't fitted 2nd additional relay for 1st stage fan, will see how this goes for a while

[HarryMann]

Just to update, when the 1st stage fan starts, via the thermo switch, my relay kicks in and ignites the bulb. So works perfectly.

Also when I flick my chicken switch, the bulb is lighting up also, aswell as the bulb on the chicken switch itself, so a nice little addition too.

Haven't fitted 2nd additional elay for 1st stage fan, will see how this goes for a while

Brill! Thanks all of you, encouraging and a good mod, esp, the tell-tale for the 1st stage...