MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB GT V8 Factory Originals Technical - Thermo Fan Switch

Where is the best place to put the after market switch,radiator top header tank or lower hose,any experience with either?
rgds Trevor
t burnett

Factory switches are always either in the thermostat housing of the head or inlet manifold or the top of the rad, with aftermarket ones that can be inserted into a hose it is the top hose. I.e. all are at the hottest point, not the coolest. If the engine produced a constant level of heat output under all conditions then maybe it wouldn't matter, but when the engine is producing more heat you want lower temperature coolant going in at the bottom, so it stays at more or less the same level coming out the top. If you maintain a constant level of coolant going back into the engine, what is circuitalting round the engine and particularly in the heads will vary hugely.
Paul Hunt

Thinking back to the 80s I seem to remember VW Rabits, along with small Itaian cars having their sensor in the lower tank and again I'm in the wayback machine,but I'm thinking it wasn't unusual. Just something to think about. Ric
RIC LLOYD

Thermo switches have to go after the mechanical thermostat on the engine. The land rover mechanical thermostat has a switch location in it's housing. The resistance of this drops to zero at 92 degrees C. Works well as a fan switch, however when I went to replace it the replacement was faulty , as was the replacment replacement, plus a third. BAD batch. The problem is that this is an M10 thread which means you must buy the LANDROVER switch, which costs $60!. An expensive game. I went and bought a davis craige adjustable version for the same price. This was an in line arrangement. http://www.daviescraig.com.au/Controller___Switches-list.aspx

You can now buy generic in line thermo switch housings. a little like the davis craig one. These alloy things can be got at most auto shops. They are sort of a hose joiner with a thick threaded bit for a temp switch. I would suggest using two fans, and two identical (around 92 C) switches places in the inlet and the out let hoses. Just pick any roughly 92degC switch that will fit into the hose joiner. The idea is that the second fan only cuts in if the first isn't cooling enough.
Peter Sherman

"the replacement was faulty , as was the replacment replacement, plus a third. BAD batch"

Par for the course I'm afraid, but if anything like brake light switches it is not a bad batch but poor design as *all* of them will be like it.
Paul Hunt

Trevor
I have found that the best place for a thermo fan temp sensor is in the bottom tank or bottom hose.
The theory being that while driving your car out on the open road the airflow through the radiator cools the water as it goes down through the radiator leaving the bottom tank and bottom hose much cooler than the top bits. Then when you come into traffic or have to slow right down there is reduced airflow to cool the radiator and the hot water enters the top of the radiator as normal but passes through without being cooled therefore making the bottom tank and hose increase in temp. This is when the fan needs to be switched on to keep that bottom half cool. It can be set as low as 70/75 deg Hooking it up this way gets the fans going as soon as airflow stops doing it's job instead of waiting for the whole cooling system to get hot which is what happens when the sensor is in the top half of the system. A lot of late model cars have it in the bottom tank and also have one in the thermostat housing for a backup. Thats my story anyway Cheers Willy
WilliamRevit

This thread was discussed between 28/04/2009 and 06/05/2009

MG MGB GT V8 Factory Originals Technical index

This thread is from the archives. Join the live MG MGB GT V8 Factory Originals Technical BBS now