16 replies to this topic

[[email protected]]

Is the factory auxiliary electric fan thermostatic sensor switch (that's screwed into the thermostat sandwich plate on a 1991 Mainstream Cooper) user serviceable?

See a new one here: https://www.minispar...c/YWL10010.aspx

My mine seems to be running the fan like it's stuck in the closed (ON) position, even when the ignition is just turned on, engine not running, not generating any heat at all.

I read numerous posts where people advise plugging the hole in the sandwich plate and installing a manual switch with an indicator light on the dash...

...but not only do I not have any empty spaces for a switch, I know I'm going to be a lot less reliable about remembering to turn it on when engine temps rise than the automatic switch would be.

So in other words, can I take the existing unit apart to get it working properly again... Or should I just buy new one? (They are pretty expensive)

[68+86auto]

I would just try to fit a different (cheaper) fan switch. It might require drilling and tapping a larger thread since m8 looks a bit unusual.

[cal844]

I just fitted a switch on the dash and monitor the engine temperatures from the guage

[Ethel]

You can get inline adapters, or  stick one of these on the radiator header, hose, stat housing....

 

You'll want normally open flavour & the temperature rating would be a bit of a guess, mine is around 100c - a thermometer could be used to make it an educated one.

 

You might even try putting the original in the freezer, but it'd ne bore of a hope & a prayer

[slidehammer]

Are you sure it is the temperature sensor? If so what about this one - https://www.minispar...|Back to search

I would resolve the problem rather than just adding a separate fan switch. The temperature sensor is also sending information to the ECU which help work out mixture (based on engine temperature)  so if the ECU is getting the wrong info it can affect other things like fuelling as well. I would fit a genuine one as well (or a Mini Spares one) so you know it is properly calibrated. 

Edited by slidehammer, 20 February 2024 - 01:23 PM.

[[email protected]]

I would just try to fit a different (cheaper) fan switch. It might require drilling and tapping a larger thread since m8 looks a bit unusual.

 

That's a reasonable idea 68+86auto, but since I've had this Mini for over a decade and it's the first time it's giving me any trouble, I'm thinking I'd probably prefer to keep things "stock" for when my daughter takes ownership (she tells everyone that "It's mine when he dies!"), so looking up parts for a '91 carb'd Cooper might be easier for her (or her mechanic) in future without having to figure out something I've altered.

[[email protected]]

I just fitted a switch on the dash and monitor the engine temperatures from the guage

 

Thanks cal844, I might temporarily do that while awaiting parts, or I might just disconnect altogether now as it's the dead cold of winter and I'm driving with the cabin heater core fully engaged. But long term, I know I'm going to be a lot less reliable about remembering to turn it on when engine temps rise in Summer than the automatic switch would be.

[[email protected]]

Are you sure it is the temperature sensor? If so what about this one - https://www.minispar...|Back to search

I would resolve the problem rather than just adding a separate fan switch. The temperature sensor is also sending information to the ECU which help work out mixture (based on engine temperature)  so if the ECU is getting the wrong info it can affect other things like fuelling as well. I would fit a genuine one as well (or a Mini Spares one) so you know it is properly calibrated. 

 

Good thought on possibilities other than the switch slidehammer, but I don't have an ECU, so that's not a factor. 

 

Mine's a 1991 HIF44 carbureted Mainstream Cooper without any of the modern engine control electronics (well, I do have an electronic Dizzy without points, but that's about as "modern" as it gets). 

 

My engine is a 12A2AG01 109771, and based on that I think my sandwich plate is https://www.minispar...c/PEM10036.aspx (from that description: "...ENGINE NUMBERS F53/GO1...").  That sandwich plate has the 8mm hole to match the 8mm sender that I first stumbled on.

 

But thanks for pointing to the alternative sensor switch... 

 

I'm going to have to look at my switch a lot closer to see if it is the "original" or if it is the one you pointed to - mine might have already been "modified" to that sensor (described as "...for fan and ECU fitted in sandwich plate below thermostat on twin point cars.") and its wiring harness (https://www.minispar.../YMQ105690.aspx)   

 

I put "modified" in quotes because if someone did switch it, it would likely have required re-tapping the 8mm hole to 12mm (like 68+86auto suggested) based on the description found on the MPI sandwich plate page: "...same caasting as other sandwich plates but has a large 12mm threaded hole in the side for the transmitter." (see https://www.minispar.../PEG100030.aspx) 

 

I am certain that I do NOT have that MPI sandwich plate because I have a side-radiator and that sandwich plate description also reads "...No hole for radiator bracket..."

  

But if someone's already done the work to change over, then that 12mm sensor and seal would be less than $20 versus $72 for the first 8mm one that I found, so thank you!

[Ethel]

I think there's some confusion creeping in here...

 

The radiator fan will be operated by a thermostatic switch. There'll be a separate temperature sensing resistor for the temperature gauge.

[stuart bowes]

any manual switch you do add even as a temporary measure would need to be rated to the right amps because a fan draws a fair bit of current

 

best case the switch gets hot, slightly worse case it melts, worst case you start a fire

 

this one should be hefty enough https://www.12voltpl...7e6Ev--2eC8qDaw and obviously sufficiently rated wiring to suit

 

obviously you can use a smaller switch if you're using it just to switch a relay which is probably the better option albeit more complicated to wire up, a lot of faff if just temporary

 

probably obvious / no longer relevant to you but pointing it out anyway for anyone who may not be aware now or in future

Edited by stuart bowes, 21 February 2024 - 03:00 PM.

[super6al]

Hi 

I had a similar dilemma when I broke the switch housing after I removed the engine. It seems to have been only used for the main stream carb coopers from 1990/1. I struggled to find anything with an M8 thread.  Have you tested the switch?. They are normally open & close when they get up to temperature.

With regards to servicing there not really serviceable, however there's not much to them. Given the cost of new ones & the alternative solutions, I figured I had nothing to lose so had a go. There are sealed unit but if you can break the black seal where it meets the brass you can access the switch. Its simple spring loaded contact actuated by a very small metal rod (as I found out its easily lost so be careful - I ended up having to make another from wire) The rod moves when the brass (via wax?) gets up to temp & closes the switch.

With the make shift rod & it glued back together , I tested it & it worked fine.

Good Luck 

[cal844]

I just fitted a switch on the dash and monitor the engine temperatures from the guage

Thanks cal844, I might temporarily do that while awaiting parts, or I might just disconnect altogether now as it's the dead cold of winter and I'm driving with the cabin heater core fully engaged. But long term, I know I'm going to be a lot less reliable about remembering to turn it on when engine temps rise in Summer than the automatic switch would be.

I just keep an eye on the engine temperature gauge, if it goes higher than 3/4 guage I hit the switch. I also have the heater that I can use to dissipate heat if needed

[viz139]

As stated above the temperature sensor in the sandwich plate does not control the fan, it is the signal for the temperature gauge only. The switch for the fan is located in the bottom of the radiator .

https://www.somerfor...-radiator-91-97

Sometimes the wire can get damaged near the end and short out causing the fan to run all the time. Remove your grill for access and than with the fan running pull one of the connectors off the switch to see if it stops. If it stops its a faulty switch if not it could be the wiring or  the relay is stuck on.

[Ethel]

I think it's a different setup (temp sensor in the head?), but a radiator with a switch fitting would be an alternative.

[roblightbody]

My late 1990 Cooper has the sand sandwich plate switch setup as the original poster. I've got all the right new bits from mini spares to replace it, although they've not been fitted yet.