Electric fan switch location

[cook1e]

The Thermostatic switch on my Pacet fan has packed up, it keeps sticking on, so time to replace it.

Rather than go for a replacement of the type I've currently got, (an adjustable switch with a Thermocouple that you shove up the top hose). I've decided to go for a more elegant and professional looking approach. I've ordered a billet ally housing and switch on ebay, the type that you cut a section out of the hose to fit, picture of the unit below.

The add on ebay states to fit it on the hot side of the radiator (the top hose), however I think it's much better on the bottom hose because:-
1. There's much more room as the top hose is quite short.
2, If fitted in the top hose t would remove the flexibilty required inthe top hose when the engine moves.
3.  If it' sin the bottom hose it will be measuring the temperature of coolant exiting the radiator and will only switch the fan in if the radiator is failing to cool sufficiently which must be the technically best solution.

What do you lot out there reckon, do you agree or disagree with my thinking?

[Nick Jones]

I think that it should be in the bottom hose because, as you say, this is measuring whether the radiator needs help.  However, this would need a lower temperature switching point than a switch mounted in the top hose.  I'll stick my neck out and suggest that a switch mounted in the bottom hose needs to operate between 70 and 75ºC, whereas one in the top hose would want to switch in the upper 80sºC.   Others may have different opinions.  I switch mine (controlled by the engine temp sensor in the thermostat housing) at 90ºC - works for me.  You should be able to get a switch with the right switch point to suit though.

Nick

[cook1e]

Nick_Jones wrote:

I think that it should be in the bottom hose because, as you say, this is measuring whether the radiator needs help.  However, this would need a lower temperature switching point than a switch mounted in the top hose.  I'll stick my neck out and suggest that a switch mounted in the bottom hose needs to operate between 70 and 75ºC, whereas one in the top hose would want to switch in the upper 80sºC.   Others may have different opinions.  I switch mine (controlled by the engine temp sensor in the thermostat housing) at 90ºC - works for me.  You should be able to get a switch with the right switch point to suit though.

Nick

Thanks Nick,

The switch supplied switches in at 90deg and out at 80deg, it's advertised as being for  GT6, TR6, TR7, Spitfire, Stag & Vitesse. This may be a little high for bottom hose working.  I'll give it a go and see how it does, I can  change it for a lower temperature one later if needs be. If the car runs to hot I can always bypass the switch manually until I get hold of one.

[Bainzy]

I bought this item and fitted it as per the seller's recommendation in the top hose. You don't want to use it in the bottom hose without replacing the switch, it takes quite a bit of time to come on as it is in the top hose.

My temp guage settles in normal running at a bit under half way - it usually doesn't activate the fan until the temp has climbed to almost 3/4. That'd be even later if I'd have used the bottom hose.

Maybe get an extra switch that comes on at about 80-85 degrees?

I agree with the point #3 you made though, let me know what temp switch you settle on as one day I'll probably move mine down to the bottom hose.

[neilnaz]

I think you should go for an adjustable version of the pictured item so you can put it in the bottom hose as I have done on my car. The one pictured looks like the Revotec controller I fitted works well and you can adjust so it comes on when you wish. Fitting a fixed controller in the wrong position will lead to constantly on or off or just right if you are lucky.... :)

[piman]

Hello all,
I believe it makes no difference in operation provided the switch is the right temperature setting for the chosen location. Remember it is the thermostat that controls the water temperature not the fan switching in or out. It is a progressive device, not something that opens when the engine warms up and stays fully open.

Alec

[rhodes]

I use the temp sender in the cylinder head with a bit of electronics.  An earlier version used a thermistor strapped to the thermostat housing.  Those devices which plug into a hose are a pain.

[uksnatcher]

This is how I mounted my fan temp sensor, tapped the thermostat housing to 3/8 bsp and used a sensor with a good temp range and short probe found the 1.0 lt 1989-92 US spec Daihatsu Charade 92-87degree (fan operates at 92 deg - switches off at 87deg) about a tenner on ebay ....and i must say works perfectly on both std and wide radiators   ;)

[Royboy66]

Cookie,

I tried a few senders in the golf rad I have fitted,

first go here to pick sender temp range
and thread size........http://www.omniautos.force9.co.uk/sprite/m_cool.htm#ELECTRIC%20FAN (click on Elec fan switches )

Then put part No in here.........

http://www.intermotor.co.uk/?p=smpeurope/catalogue&brand=intermotor&SESSID=d6bdibfmopn7o3ng7gd66qgmv5&SESSID=0812hdkvh735ji6c7u9t75cqj1

Then you can get the sender from  your local motor factors or ebay or wherever suits ya !  ;) :)

[cook1e]

Cheers Roy Boy, that links really useful! I was trying to find something similar through google last night without success.

[shedmonkey]

cook1e wrote:

The Thermostatic switch on my Pacet fan has packed up, it keeps sticking on, so time to replace it.

Rather than go for a replacement of the type I've currently got, (an adjustable switch with a Thermocouple that you shove up the top hose). I've decided to go for a more elegant and professional looking approach. I've ordered a billet ally housing and switch on ebay, the type that you cut a section out of the hose to fit, picture of the unit below.

The add on ebay states to fit it on the hot side of the radiator (the top hose), however I think it's much better on the bottom hose because:-
1. There's much more room as the top hose is quite short.
2, If fitted in the top hose t would remove the flexibilty required inthe top hose when the engine moves.
3.  If it' sin the bottom hose it will be measuring the temperature of coolant exiting the radiator and will only switch the fan in if the radiator is failing to cool sufficiently which must be the technically best solution.

What do you lot out there reckon, do you agree or disagree with my thinking?

I used one of those in the top hose  whilst on the 10cr (1500 standard spit no engine fan twin 9" fans mounted on wide 3 core rad)  no over heating prob at all and it had its ARSE caned to an inch of its life (its non OD!)  up all the mountains and along the motorways I agree its bloody tight in the top hose and I took a spare rad as I was worried the lack of flex might shag/snap  the top rad pipe but no prob, but I think for peace of mind I will fit a switch into the rad header tank section -rubber bumper MGBs use a push in self sealing switch just got to pluck up courage to drill a hole in my new rad!!!!

[GT6 M]

My self, I would set it to come on at about ,  or just over what the engine runs at.
reason, it takes a wee while for the temp to actually come doon, so it will not let it get into 3/4 hot areas.

[mpbarrett]

rhodes wrote:

I use the temp sender in the cylinder head with a bit of electronics......

I have done the same. I use the voltage across the normal temp sensor, I have replaced the mechanical voltage regulator with a linear regulator and use small PIC cct with adjustable On and Off tempertures ( and a series of 3 LEDS to show what its doing...). Checked it with a seperate thermocouple strapped to the thermostat housing and it seems to work very well.
Still have a manual ON/OFF switch just in case :)

Mike

[TimW]

I use an 85deg switch in the bottom of my civic rad.  This switches the fan on when the temp on the gauge is a needle over half.  It works perfectly until the fan fuse blew on the motorway in sitting traffic in Italy on the 10CR!  WOW what alot of steam!!  On a hot day my temp gauge usually sits at a needle under half while cruising.

[uksnatcher]

Thanks tim...wondering what temp sensor is needed after the rad has done its job...

So .....its looking like a sensor needed so fan turns on at 85deg in bottom hose/bottom of rad..... and 92deg in top hose/thermo housing going of mine and your findings.

[TimW]

Hey Gary

normal operating temperature for most engines in 90deg  I don't think it would cause much problem to use anything from about 85ish to 92ish in the bottom.  As long as the tempreture of the engine doesn't go over about 103ish it shouldn't boil over.  At the end of the day thats all you need the fan to do, keep it from boiling over in the worst conditions on the hottest day.

My tempreture varies so much from just below 1/4 to just on 1/2 depending on the conditions.  I do have a 78deg (i think, well lowest i could find) thermostat  so this may also contribute to my varied tempretures.  While on the 10CR in 37deg weather going up the passes the fan was on all of the time and once the heat soak had built up it didn't drop from 1/2 no matter how fast i drove!!

Next time we meet i expect to see you in your spitfire!! 8) 8) 8) 8)

[tiggrr1]

339 wrote:

Next time we meet i expect to see you in your spitfire!! 8) 8) 8) 8)

He's never out of the thing  8) 8) 8)

Unlike me, I may get the GT6 out of the Garage for the first time since the 10CR tomorrow  :B :B :B

It does need all of the Euro crap washing off and a run out.

[cook1e]

339 wrote:

Hey Gary

normal operating temperature for most engines in 90deg  I don't think it would cause much problem to use anything from about 85ish to 92ish in the bottom.  As long as the tempreture of the engine doesn't go over about 103ish it shouldn't boil over.  At the end of the day thats all you need the fan to do, keep it from boiling over in the worst conditions on the hottest day.

My tempreture varies so much from just below 1/4 to just on 1/2 depending on the conditions.  I do have a 78deg (i think, well lowest i could find) thermostat  so this may also contribute to my varied tempretures.  While on the 10CR in 37deg weather going up the passes the fan was on all of the time and once the heat soak had built up it didn't drop from 1/2 no matter how fast i drove!!

Next time we meet i expect to see you in your spitfire!! 8) 8) 8) 8)

Billet adaptor arrived today and the temp switch as supplied comes on at 90 deg and turns off at 83 deg. The instructions definitely say fit to the top hose but I still reckon it'll be better in the bottom hose I think I've got a spare bottom hose to give it a try out. They also say you need to use a relay whereas the original Pacet capillary one supplied with the fan wires straight in.

[Nick Moore]

Cookie, I suspect that by the time the water coming out of your radiator is 90C, the water at the top will be about 100!

My Herald's wide radiator has two fans, and I took the opportunity to fit two switches. Both are set to kick in around 80C. The left hand fan, activated by the top switch, kicks in right on cue, but I've never seen the right hand fan, switched from the bottom hose, kick in by itself - and that's in tropical Australia! The temperature drop across the radiator is too great. Both temperature switches have been tested and both do work. So, I'd put the switch in the top of that radiator. That's what I've done in my GT6-3.