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Temp Sensor for Electric Fan

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71tr

71tr

Jedi Warrior
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There have been a number of posts regarding electric fans and aluminum radiators fitted to the TR6. Mounting of the electric fan temp sensor is typically a new bung on the radiator or in-line on one of the radiator hoses. Is there anyway to take advantage of the existing temp sending unit near the thermostat housing? Perhaps substituting the electric fan sensor and wiring it to the temp guage or some dual setup accessing the water channel at the existing location?
 
The only problem that I see, and this is purely speculation, is if you mount it at the top of the radiator in the top tank, you run a very slight risk of if the radiator should run low, you lose your sensing ability, plus you need a really hot sensor to not go on when the coolant is at its hottest, at the top. I welded a bung in the return pipe at the bottom and mounted it there, no cavitation of fluid and used a 160* sensor (or was it 180*?).
 
Bill,
I know you got the Spal sensor kit because you recommended that to me, they only have two choices either 185* or 195*C kits.
 
I do not think the gauge sensor location will work as it is before the thermostat -- depending on what temp setting you use you could have the fan coming on before the tstat even opened. Not a problem, just useless.

I would think the lower end of the rad would be the best place for the sensor as you want the fan to come on when the radiator needs the help.

If the sensor is at the top of the rad it seems the fan may come on when the engine is hot even though the radiator is successfully and adequately cooling... since a usual reason for an electric fan is to not have the fan taking HP at speed this condition would seem to be undesirable.
 
Have we noticed Paul's new Wizard rad post? And what they've decided the switch/sensor location should be and why?

Besides: ~IF~ the switch ever ends up without coolant covering it, you still have a GAUGE to tell you it's hotter than it should be. That would indicate something's wrong.
 
Some folks are putting the temp sensor in the bottom of the radiator, others at the top. I used to think the top location was proper since that is giving you a true reading on coolant temp before the radiator does its work. But Geo's comment about locating at the bottom to tell if the rad needs help makes sense. My question was inspired by Paul's Wizard photo showing his temp sensor in the top of the rad and only 12" away from the factory gauge sensor, but didn't consider which side of the thermostat each resided.
 
With the sensor at the top (and assuming it a properly maintained and monitored cooling system) the fan switch will be fed the engine's current running temp. If it gets to threshold the fan is turned on until it hits the lower end of the range. With the sensor in the bottom run from the rad the switch is monitoring rad temp and would come on later than if mounted at the top. I suppose it's all in what you consider to be prudent for the setup you're running but mine would be monitoring engine temp to determine when the fan came on.

In truth, I simply have a switch and watch the gauge. No sensor.
 
And of course in the 'top vs bottom' choice you would likely use a different temp sensor depending on where it was located... i.e. a lower temp sensor if the location is at the bottom of the rad.

But I, too, just use a manual switch which has the advantage of letting you anticipate the need (like when you're looking at 25 miles of up hill road).
 
Yup-yup. I rarely encounter conditions to warrant the "extra" fan, but stop-and-go Florida traffic in July is sometimes encountered. That extra bit of air flow has kept me sane at those times... *click!*.... aaahhhh... :smirk:
 
All of the guys at Wizard said to mount it in the top for the exact reasons that Doc stated. So I did, and also because they did not want to put it anywhere else.

I will have a lighted over ride switch just in case, but it will run automatically for the rare day that my wife may decide to go to Newport for spin with one of her girlfriends.
 
I have had a little extra time on my hands while I am in Singapore and since the main point of the all the radiator temp switch location discussion seems to be where to get the most accurate temperature.
I have started to investigate using the signal to the temperature gauge from the temperature sender as a source to trigger the fan on and off. This would be the most accurate temperature reading for actual engine water temperature.

It looks like you could make a voltage comparator circuit to monitor the voltage to the temp gauge. Per a Dan Master's article when the temp sensor unit is at 100 Ohms the gauge is at a little over 1/2 scale, and 50 ohms is full scale.
So around approximately 90 ohms would be the right place to trigger the fan on. This voltage comparator would monitor the voltage change across the gauge and switch on, but it would also need some hysterias so it would not switch off at the same point it switched on. Or have the switch off function controlled by the radiator temp. I am not sure of the voltage levels because I think Dan's article indicates he had a 100 ohm resister in series with the gauge between the gauge and ground for test purposes, that would change the current values. This is the article I am referring to. https://www.tr6web.com/Documents/tr6/gaugetesting.html
A circuit similar to the one in middle of this page https://home.cogeco.ca/~rpaisley4/Comparators.html
could be modified and use to drive a transistor that could handle the relay coil draw.
Comments?
Hmm interesting.
 
I took the radiator top hose thermostatic vacuum switch T-fitting from a late year donor TR6 (see TRF Spare Parts Catalog, Volume 1, the Blue Book, Plate "CC")) and installed it in my top hose, retaining the existing temp sensor below the stat housing. I replaced the vacuum switch with a temp sensor to operate the e-fan. This nets me two sensors; one added for the e-fan and the other original equipment for the temp gauge. The e-fan wires are neatly tied as they go from the fan to the sensor and then the power source crossing open air near and under the 55 amp GM alternator. The ground wire was located near by.
Once I convert to EFI, I will be faced with the problem of locating another temp sensor again. But for now, this works for me just fine.
 
I agree with Paul.....if Wizard makes the radiator & installs the bung at the top they do it for a reason and that was good enough for me. I actually have 3 coolant sensors: Original one for the gauge, Wizard one and one for the TBI conversion in the hose coming out of the thermostat. My Spal fan is wired with a 3-way switch: auto, on and off. The off position assures that it won't accidentally come on when working on the car. I also have it wired to the old EGR dash light so the light comes on when the fan is running. What amazed me is how infrequently the fan runs and if I'm going over 35 mph, it "never" comes on.

Here's my 3rd coolant sensor.
Coolant%20Sensor.jpg
 
<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I agree with Paul.....if Wizard makes the radiator & installs the bung at the top they do it for a reason and that was good enough for me.[/QUOTE]

Except of course they put it on the bottom for me, so I guess it depends on what day you order one (but then I had to send them an old rad to get the dimensions right, so perhaps I got an early production model)...

Actually if you really want an accurate reading, you can do what they did to mine when they were trying to get better numbers for the ECU.

They tapped the takeoff from the waterpump to fit a standard GM type sensor for the EFI, and they brazed the original into the freeze plug at the back of the engine for the gauge. If you aren't getting engine temperature there, I don't know where you are!
 
And you are subtlety trying to badger me into fuel injection, Alan??

I think not.....too many sensors for me.
 
Paul said:
I think not.....too many sensors for me.
Click to expand...

:iagree:

Keep these old YesterTech lumps SIMPLE! :thumbsup:
 
DrEntropy said:
Paul said:
I think not.....too many sensors for me.
Click to expand...

:iagree:

Keep these old YesterTech lumps SIMPLE! :thumbsup:
Click to expand...

And you think triple carbs are simple? Then you should have shown the mechanic that screwed mine up how to tune the buggers.

At least FI once tuned is true plug and play. If a bit goes wrong replace it and it all works again.

And no Paul, I think you should stay with carbs. I like that fact that FI isn't common :wink: The last thing I want is people seeing how well it runs so it becomes commonplace. What fun would that be for me when I open the bonnet :laugh:

My point was only that since even the radiator manufacturer can't seem to decide where it wants the bung, so why should anyone else be able to say definitively where it should be.
 
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