Electric fan turn on / off sensor switch issue

[UKPhilTR7]

I have an electric fan fitted with a turn on / off sensor switch in the top hose, as shown in the picture below. The fan has stopped turning on automatically now and I was thinking the sensor may have gone. The fan can be turned on manually by a switch in the dash, so the fan is all OK.

Is there an easy way to?

Check the switch is working by connecting it to a multimeter and seeing if current is allowed through when it gets hot enough and turns on?

Checking what rating thermostat I have, without taking the whole of the housing off and taking it out? I think I have the 82 oC one fitted.

Does anyone know where I can get the correct sensors from and would I be right in thinking I would need one that turns on at 90 oC?

https://www.ebay.co.uk/itm/30MM-HOSE-ADAPTOR-ELECTRIC-FAN-SWITCH-TR6-TR7-GT6-SPITFIRE-VITESSE-STAG-MLR-JP/401377798324?hash=item5d73fb28b4%3Ag%3AdrkAAOSwa~BYV-ye&_nkw=tr+electric+fan+sensor&_from=R40&rt=nc&_trksid=p2380057.m4084.l1313.TR12.TRC2.A0.H0.Xtr+el.TRS0

[busheytrader]

Hi Phil,

I had a similar issue.

I placed the thermostatic switch in an old mug, connected a multimeter to it, then filled up the mug with boiling water. The switch should complete the circuit in a few seconds then cut the circuit as the water cools. If not it's duff. If it works and you want to be more precise on the temps, put a thermometer in the mug.

A cheap hand held infra thermometer can give a good idea if your thermostat is opening in the right ball park. https://www.ebay.co.uk/p/Non-contact-LC ... 6effed2d70 I bought one cheap from Maplins but they went bust recently. Point it at the thermostat housing when hot water starts entering the radiator and check the reading.

Replacement switches that turn on the fan around 90c are readily available Back here in Blighty. I've read a number of articles that state they should turn on around 8 to 10c above the thermostat opening temperature (assuming that the right stat is in situ). My own turns on at 90c, the stat opens at 82c.

Hope this helps.

Adam


https://www.ebay.co.uk/itm/ELECTRIC-FAN ... SwBahVNnSx

[Beans]

Thermostat should open at 88ºC on the later cars
If that gives problems with the temperature there's something wrong with the cooling system
Also the temperature should remain steady under all conditions

[UKPhilTR7]

Thanks for the links Adam. I was thinking of the hot water trick. Currently, I have to get her to ready for shipping and the last thing I want is for the engine to overheat while they move her.

Was thinking if bridging the two wires together and making the fan on all the time. That would be better while shipping than her blowing. However, with the switches that price I may be able to get one here before she gets packed.

Thanks for confirming the temp on setting I need. I see the one that you posted was a M16 thread. I am not sure what mine is but would imagine that is right. I will be squeezing the top hose together between the switch so I can take it out and not have to replace the whole cooling fluid. That is a job for when back home.

[UKPhilTR7]

Thermostat should open at 88ºC on the later cars

I always thought it was around 82. What makes the older car (engine) better than the earlier car engines (to go to 88),, improved rad?

If that gives problems with the temperature there's something wrong with the cooling system
Also the temperature should remain steady under all conditions

I have always found statements like this to be very open ended. Like now, if I was to read your exact words, I would start to worry about mine. As if left running she will creep up. However, mine is not moving so not got the air flowing over her and my viscous is not conceded, so nothing pushing air over the engine. Are your words made from the angle of the viscous running and under normal driving conditions?

[UKPhilTR7]

Just looked at the settings for the one you posted Adam and it says on at 90 and off at 80. Was that just a guide or would we need one that comes on and off a little later if our thermostats (on the standard 2lt) open at 82?

[busheytrader]

Hi Phil,

It was just a generic item from the eBay seller highlighted in your first post. I've bought a couple of items through them in the past. A motor factors may have an OEM temp switch that's the right thread and temp range to suit your wedge for a few pounds.

I believe carb'd Rover V8's were fitted with 82c stats which later increased to 88c when they became fuel injected, in common with other manufacturers. I didn't know that this happened with the last of carb'd wedges.

[dursleyman]

Phil, If you get the Revotec version of the one in your original post it has an adjustble thermostat so you can set it to your chosen temperature. Nice piece of kit.

https://www.ebay.co.uk/itm/Revotec-Elec ... otec+.TRS0

[Beans]

.. I didn't know that this happened with the last of carb'd wedges ...

I always thought that the thermostat change (82ºC > 88ºC) coincided with the cooling system change
But I have a 1975-1976 workshop manual that states a 82ºC thermostat only, all other manuals I have state the 88ºC one
So it looks like the change was made much earlier in the production, well before production was moved to Canley

[UKPhilTR7]

I was looking at the Revotec item as Robsport sell them. However, I have the Kenlow fan and controller fitter, so fitting the Revotec o e would require a bit of retro fitting. That may be a job for after she is backin the UK.

I did see I and thought that it may be a bit better with the on at 90 and off temp around 80, rather than coming on at 70.

[busheytrader]

It looks like the Rovotec item has a variable range that starts at 90c.

Id rather have one of those than my existing unit. It has one of those capillary probes that fits in to the top hose under the hose clip. It takes a while to get a 100% seal

[UKPhilTR7]

That is my thinking on this. If you have a thermostat that opens at around 82, you need the fan to come on around 90 and off at 80.

Surly if the fan is kicking on at 80 and going off at 70, the engine is not up to temp and the fan is keeping things too cool.

The Revotec item does look nice. It would mean taking my old Kenlow controller unit out though and retro fitting. Will have to look further into that.

[FI Spyder]

They needed higher engine temp's to meet tougher emission standards so thermostat value was raised. If the thermostat opens at 88C and your fan doesn't turn off till 80C that means most of the time your fan will be running when the water isn't flowing through the radiator which doesn't make sense. Why would you want the fan cooling the radiator when it's effectively blocked out of the cooling system? Coolant boils at 129C and even higher in a pressurized system under 15/16 pounds pressure so you have lots to play with. The cooling system on a 7 is pretty efficient. The difference between running the car just above freezing ambient (at which point the thermostat is barely open) and 30C+ in stop and go driving is about one needle width with that needle resting just over 1/4 on the gauge. The gauge is measuring resistance in the circuit so the rest (meaning normal operating) position will vary from car to car depending on resistance of the particular temp sensor, resistance of the wiring and connections of that wiring, the particular characteristics of the gauge and clean connections so that the circuit is getting full 12V and not some less resistant limited amount. Only an infrared thermometer can give you an actual temp reading. As Beans said, if you have cooling problems, it's not because of the thermostat. If the thermostat fails they are designed to fail in the open position. In the case of the slant 4, the thermostat should have the "Triumph foot" to block off the bypass flow when open, otherwise only part of the coolant gets directed through the radiator (not sure about the Rover V8). The V8 cooling system had a problem (and to lesser extent) of air getting trapped in the system which in effect blocked good coolant flow. It is important when flushing system, to make sure there is no air trapped in the system (that technique is for another time/post). Small pockets (bubbles) of air can be expelled into the expansion tank with normal driving and the coolant flow from the water pump but larger pockets can stay trapped and is not good.

[saabfast]

Coolant boils at 129C? Is that not allowing for the pressure rather than the pressure increasing it further?

There are lots of theories. My electric fan is operated by a capillary bulb in the top hose (not had a problem with sealing it though). There are no temperatures on the adjustment scale and I cannot remember if the Dt was ever in the blurb. Without worrying about temperatures I have it set to switch the fan on at just under half on the gauge and it goes off around halfway between quarter and half. It only normally comes on in traffic as the ram air flow is generally sufficient, so it basically reflects the operation with the original fan and most of the time the car runs with the needle halfway between the quarter and half marks as it did originally.

[FI Spyder]

Coolant boils at 129C? Is that not allowing for the pressure rather than the pressure increasing it further?

You're right I didn't see the asterix on the label. That's at 15 lbs pressure. As pressure caps can range from 13 to 22 lbs. pressure (on the few I checked) that 129C will vary quite a bit depending on cooling system. The higher the pressure the higher the boiling point.

If the thermostat opens/closes at 88C if the fan is running below these temperatures it is doing no good as there is no coolant running through the radiator to cool. It will just cool the coolant already in the radiator but that's not going through the engine. It would seem to me to be more efficiant to have the fan turn off at or just below the thermostat value rather than 80C(unless your running a 82C thermostat as you are close to the 80C at that point).

I didn't realise how much difference the thermostat made until it failed in my '91 Integra. Although above freezing (typically 6C here) I could get no heat through the heater until it was replaced. Just the normal flow of the coolant through the small rad (no fan) prevented it from warming up enough to make the cabin heater effective.