fan switches

[morris]

evening all, after a bit of a lull in activity due to a frustrating drain on my wallet for endless other things, my remortgage has come through so I can crack on again.

I've installed my new rad today and need to get the fan side of things sorted out. When looking at fan switches they seem to specify a higher number and then a lower one. I'm currently assuming that the higher number is the value at which it will switch the fan on and the lower one is the temp that it has to drop to before switching back off again. Is this a safe assumption or is it a dual speed switch?

The Bentley manual states the donor fan was 91 deg C low speed and 99 deg C high speed so I guess I need to aim for the lower number if only one speed is available.

Any recommendations out there on the best fan manufacturer to go for?

[Mike]

Originally Posted by morris

I've installed my new rad today and need to get the fan side of things sorted out. When looking at fan switches they seem to specify a higher number and then a lower one. I'm currently assuming that the higher number is the value at which it will switch the fan on and the lower one is the temp that it has to drop to before switching back off again. Is this a safe assumption or is it a dual speed switch?

The Bentley manual states the donor fan was 91 deg C low speed and 99 deg C high speed so I guess I need to aim for the lower number if only one speed is available.

Any recommendations out there on the best fan manufacturer to go for?

Ian
The two values are for two speed fans. As you suggest, I've taken the lower temp to bring my fan on, but intend to monitor it once I get on the road. I calibrated my guage quite accurately at 100 deg C, by using a small resistor in series.
I went for the largest diameter Pacet fan that I could fit - I even designed my radiator to maximise the fan size - on the basis they are prepared to tell you what their fans will pull/push per minute - and that M50 heads do not react well to being over heated. My 12" is rated at 2,000 cubic feet per minute - should keep it cool!

Are you planning on wiring it through a relay?

Mike

[morris]

ok, so need to find a 99-91 switch and I was planning on using a relay so I guess you need two for that setup and just one if going straight for a single speed at 91 degs C. I'll check the bentley wiring diagram to see how it all connects up.

did you manage to get anywhere running your gauge with the in-head bmw sensor in the end? I don't have much room left to sneak a separate sensor into my top hose so would prefer to use the original

[Mike]

Originally Posted by morris

ok, so need to find a 99-91 switch and I was planning on using a relay so I guess you need two for that setup and just one if going straight for a single speed at 91 degs C. I'll check the bentley wiring diagram to see how it all connects up.

did you manage to get anywhere running your gauge with the in-head bmw sensor in the end? I don't have much room left to sneak a separate sensor into my top hose so would prefer to use the original

I have used a radiator mounted switch to control the fan - I believe that is how the donor is set up? (although I never had a donor to look at!) I added another port to my radiator to allow a standard Ford sensor to screw in to the rad.



I am not sure whether the port should be at the top or bottom of the radiator - or even if it makes any difference? Mine seems to work OK, cutting in and out, when left idling on a hot day. (Make sure your header tank is above the top of your radiator - mine eventually boiled after several heat cycles due to a lack of water left in my radiator - I've now made a new header tank, and lifted it higher).




The sensors in the head are for fuel injection temperature monitoring, and the temp gauge: they are not the On/Off switch for the cooling fan. I had to use the Smiths sender, as I had already bought a Smiths Classic temp gauge. In hindsight I would have spoken to Caerbont direct and ordered a VDO compatible version of the Classic temp gauge and then used the standard BMW water temp sender which is fitted in the head. The Smiths one is a pain - it has to be run off a stable 10v supply, so a special regulator is required, and the Smiths sender has to be fitted into a special thread adaptor collar, which does not allow the thermal head to reach far enough into the head.



I spent a couple of hours adapting/minimising my collar to allow the sensor to reach just 10mm further into the water course, just to give it more of a chance to read correctly.



If it does not work well enough, I have been advised I can get Caerbont to convert my gauge to a VDO gauge - for the price of a new gauge!

[morris]

my rad has an M22 port installed in the top tank so that's more a case of just selecting a suitable fan switch. good to know that there are options for getting a gauge to suit the bmw in head sensor as I would prefer to stick with it and get the most accurate reading. it was the smiths classic range I was planning on buying so I'll bear in mind when ordering

[GreatOldOne]

Originally Posted by Mike

I've now made a new header tank, and lifted it higher

Ooooooh! Shiny!!

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