Is your rad like this?

[Ian65]

That looks like a control switch for an electric fan. Possibly from another model of Mazda or later RX7 as I don\'t think any FB\'s had other than the \'vicious\' fan? Certainly Series 2\'s and Series 3\'s were viscous.

Tag a multimeter on it and see if it switches i.e. contacts inside, or whether it\'s a thermistor inside, in which case a sensor. The big fat spade contacts say \'switch\' to me.

put the multimeter on it and with the rad cold, there\'s continuity across the terminals.
with the rad hot, still continuity?

[David Nock (RIP)]

Rig up a test bulb from an in-line fuse off the battery. The old style 2.2watt MBC cap bulbs are ideal.
Just shut the bonnet gently with the bulb poking out in front of the driver and go for a night trip.
Does the bulb ever go out? (thinking the rads not hot enough yet - it would need to be quite hot to bring the fan on?).

Does the bulb dim or brighten? (in which case it\'s a probe not a switch).

But my guess is still that it\'s a switch, maybe arranged to operate via a relay, in fail safe mode....a broken switch would bring on the fan in that case. Maybe it\'s just a faulty switch? Doesn\'t look like it will come out without a fight.

[Ian65]

I\'d just come home from a 50 mile trip when I took the \'hot\' reading so it was about as hot as it\'s going to get.
I\'m in 2 minds about swapping this rad to my black car. I like the idea of a built in switch that I could utilise for the electric fans but the recore rad will probably be in better condition and as you say David, the mystery sensor  looks like it will take some getting out.

[captainbizzaro]

Will the height of your Rad be a problem Tim?
Series 2 has the oil cooler under the rad whereas the S3 has it integral with the engine.
Since the S3 rad still occupies the whole space, then that suggests the S2 is shorter?

Thats a fair point David, what do you reckon Ian any thoughts?

[Ian65]

The radiator on my car has what looks like a temperature sensor top left next to the radiator cap. Its not connected and isn\'t used...





I managed to buy a used but re-cored 1st gen rad off ebay for 0.99p..... a bargain!

but this rad doesn\'t have the temp sender that the other rad does....





From what I can gather, this seems to be the standard rad and the one with the top left temp sender seems less common.

Which rad have most people got...?
How come there are 2 different types....?
What\'s the temp sender for as the main temp sender is on the engine...?

Any ideas???

Sussed this out, it\'s a series 1 radiator.
The series 1 had an emission control system where the trailing plugs didn\'t fire under certain conditions apparently. This sensor on the rad was known as \'no.2 water temperature switch\' and was part of this system.
Series 2 & 3 cars didn\'t have this and all 4 plugs fired under all conditions.
( another bit of useless information that might help someone, one day!)
.

[myatt1972]

Every day a school day! I love to learn new useless info.

[Ian65]

Every day a school day! I love to learn new useless info.

That\'s good \'cause I\'m full of it!