Fan thermo switch

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Llessur
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Fan thermo switch

#1 Post by Llessur » Tue Sep 18, 2018 3:48 am

My latest 2500 project has an electric fan fitted in front of the radiator but it looks like the thermo switch gave up the ghost a long time ago - the fan is simply hard wired into a switch that floats around under the dashboard somewhere.

The fan works fine so I'm going to replace the thermo switch but I've had a couple of bad experiences in the past with temperature probes that slid into the gap between the top hose and the radiator inlet - even with great daubs of sealant it still manages to find a way to leak eventually.

Has anyone ever used one of these kits which allow you to fit the probe into an adaptor which is then fitted at the midpoint of the hose?

https://www.ebay.com.au/itm/DAVIES-CRAI ... SwPhdVD~84

It's available in a kit including the temperature controller:

https://www.ebay.com.au/itm/DAVIES-CRAI ... SwSlBYzzfs

Also, that age-old question: should the switch be fitted to the top or bottom hose for best performance?

Either way, does anyone know offhand what the diameter for the top/bottom hoses on the 2500 are? The kit says it's suitable for 32-40mm diameter hoses which sounds about right.
Adelaide, South Australia (ex-Brighton, UK)
1977 2500S - White

My 2500 blog: https://triumph2500blog.wordpress.com/

johnnydog
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Re: Fan thermo switch

#2 Post by johnnydog » Tue Sep 18, 2018 9:54 pm

Without going and measuring the top and bottom hoses physically, I know that the stainless jubilee type clips I have recently fitted have 40 stamped on them, and they also state 30 - 40mm size; presumably suitable for hoses between those sizes externally. They fitted snugly, with about 5mm excess when tightened. Used them on top and bottom, plus the PAS jointing pipe.
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1967 Mk1 2000 in Gunmetal Grey
1969 Mk1 2000 in Royal Blue
1970 Mk2 2000 in Valencia Blue
1972 Mk2 2.5 PI in Triumph White
1973 Mk2 2.5 PI in Sienna Brown
1976 Mk2 2500S in Carmine Red

tony
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Re: Fan thermo switch

#3 Post by tony » Wed Sep 19, 2018 3:43 am

The original S one was fitted in the 1/2" hose that runs from the thermostat housing to the inlet manifold. Both N.Z. and Aussie one's had these fitted . You should be able to pick up a second hand one fairly easily I would think.
Tony.
1976 2500 TC. converted to S specs.

Lots of bits

1999 BMW Z3.
2006 BMW 325ti.
Hopefully not needing too many bits.




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Clifford Pope
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Re: Fan thermo switch

#4 Post by Clifford Pope » Wed Sep 19, 2018 8:39 am

There's discussion here on the TR forum. The most favoured arrangement seems to be a stainless steel hose section with a boss for the sensor.

There's endless discussion on different forums on the top/bottom controversy.
My view is that there are two operations here:

1) The engine heats the water in the block. The thermostat determines the running temperature, and passes any surplus heat to the radiator. The radiator's job is to dispose of that heat to the air, by natural flow and assisted by the fan as required. It would be inefficient if it tried to cool the water too much, because the engine would then need to heat it up again.

So the fan thermostat's job is to optimise the temperature of the water flowing from the radiator to the engine. Hence a sensor in the radiator itself or the bottom hose makes most sense to me.
That said, any location seems to work well enough, presumably because the temperatures in any of the 4 candidate positions will all tend to move in line, although they will each be different. (engine block, top hose, radiator, bottom hose)
But it would surely be a mistake to try to use the fan to control the engine temperature. That would simply be competing with the ordinary thermostat, and not very accurately because it doesn't sense engine block temperature anyway.

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Alec
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Re: Fan thermo switch

#5 Post by Alec » Wed Sep 19, 2018 11:55 am

Hello llessur,

Cliff gave a very good description of the workings of the cooling system.
My choice is to sense the top hose as this is relevant to engine temperature. The bottom hose will have differing temperatures depending on how well the radiator is working, i.e. in hot weather the bottom hose will be hotter in relation to the top hose and vice veras so the fan control will not be as consistant. That said my reason is theoretical and with a seviceable cooling system I suspect there will be no noticeable difference.

Alec
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MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.

Clifford Pope
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Re: Fan thermo switch

#6 Post by Clifford Pope » Wed Sep 19, 2018 4:56 pm

Alec wrote:
Wed Sep 19, 2018 11:55 am
The bottom hose will have differing temperatures depending on how well the radiator is working, i.e. in hot weather the bottom hose will be hotter in relation to the top hose and vice veras so the fan control will not be as consistant.
I'm not sure you want it to be consistent? If the bottom hose is hotter in hot weather don't you want the fan to cut in?

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Alec
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Re: Fan thermo switch

#7 Post by Alec » Thu Sep 20, 2018 10:06 am

Hello Cliff,

not if the temperature of the engine is what it should be. Really the fan should only run when stationary or in very slow moving traffic. I know my fan rarely runs at all.

Alec
0465

MK1.5 2.5 P.I.
Jaguar MK 2 (Long term restoration.)
Hymer 564 Motorhome.

sprint95m
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Yes......

#8 Post by sprint95m » Fri Sep 21, 2018 3:42 pm

Llessur wrote:
Tue Sep 18, 2018 3:48 am
Either way, does anyone know offhand what the diameter for the top/bottom hoses on the 2500 are? The kit says it's suitable for 32-40mm diameter hoses which sounds about right.
32mm bore.

Please note that hose measurements are given as the internal diameter, whereas pipes are sized as outside diameters.



My advice is to steer clear of Davies, Craig and their products altogether.
You don't need a "controller", it is a gimmick. All you need is a thermoswitch which operates at the required operation for your application
(this depends on the thermostat you have fitted to your car).

I have not tried this this, but I imagine a standard 2000/2500 top hose is not very practical for an inline switch housing?
It will be possible to make up a bespoke solution from silicone hose work though, I am sure.

I concur with Alec, a correctly set up electric fan will hardly ever come on at all and never whilst the car is moving freely.




Ian.
Owner of a 1979 Dolomite Sprint (EFI),
previously ran for nine years a Dolomite (1850), a 2500S (for 4 years), a Dolomite 1500HL (for a few months),
a Dolomite Sprint (for 10 years) and a second 2500S (for 5 years until 2007).

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