I want to fit a fan switch in the bottom hose of my wifes spitfire.
At present it has one in top of the knackered rad, 90/85, but I am fitting a new rad and the best solution is the bottom hose. But what temp range? Thinking about 10 degrees different, but that is not based on anything except gut feeling. The thermostat is an 82degree.
Ta!

I think I would buy one of the adjustable ones,see how it goes then and alter it to get it how you want

I would guess 10deg lower would be too much,and the fan would be running a lot

The quality of the probe type adjustable switches is questionable at best, and I have had issues getting them to seal satisfactorily in the past, so am loathe to try again.

The figure of temp difference seems elusive, despite google searches. The engine must heat the water a fair bit, and that would be the temp difference. I will have a look and see what switches I have as a starting place. I could even try the mini/mgb type switches that seem to just have a hole in the rad and a grommet, they must work but it never seems right!

I was thinking of the inline adjustable ones,not the probe ones

as you fit a new rad, make sure it has a M22 thread on the bottom chamber...than i would install this (adjustable) one:

http://www.rallydesign.co.uk/product_info.php?products_id=13319

not the cheapest solution, but the neatest, imo.

I am of the view that its just as important where it is in the system as what temp it is.

Readings with an infra red showed t hat the cylinder head can be near boiling while the rad bottom is just warm.



Having no threaded hole rad mount I opted for a Volvo sender in the top rubber hose.

I have heard from another spitfire owner, who has done something similar and done the experimenting already. He recommended an 84degree on switch, fitted in the bottom hose. Seems the rad drops about 8 degrees , measured with his cheap IR thermometer. That is good enough for me, allbits and bobs should be here for the weekend.