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horvath 03-29-2004 09:07 PM

Electric Fan Temp. Sensors
As you may have notice by my previous post, I've just put a 16" electric fan in with a new Walker radiator. I was having some problems with my voltage and discovered it was all due to a bad circuit breaker for the fan. All is well now!

But now I'm disturbed by the temp. readings I'm getting on my temp. gauge. The temp. sensor for the fan is suppose to turn the fan on at 190* and off at 170* ... it turns the fan on at 190* alright, but my temp gauge goes all the way down to 120* before the fan shuts off and it seems my engine is spending more time in the cooler temps than it is in the 180* area, which is most desirable, right?

So I've been digging around the knowledge base, looking to educate myself about temp. sensors and getting nowhere fast.

Can anyone help me understand these puppies? What are the different kinds available? What are the best types to use? Should my temp gauge be reading so low before the fan shuts off? Isn't it best to keep the temp around 180* as much as possible?

54 Chevy Pickup

Frisco 03-30-2004 03:51 AM

If the fan temp switch is mounted in the side of the head, that area will be hotter than if it had been mounted in the intake.

Example Only: Coolant Temp in cylinder head is 210.
Coolant Temp in intake is 180.

The temp difference you are seeing seems to be on the extreme side; but if the two senders are not mounted in a similar location you will see a difference in the readings.

horvath 03-30-2004 10:23 AM

Thanks, Frisco

My fan sensor is in the intake ... my gauge sensor is in the head -- is there any reason why I shouldn't hook up my electric gauge to the electric fan temp sensor and get both happening from one source?

54 Chevy Pickup

Frisco 03-30-2004 12:29 PM


Originally posted by horvath
Thanks, Frisco

My fan sensor is in the intake ... my gauge sensor is in the head -- is there any reason why I shouldn't hook up my electric gauge to the electric fan temp sensor and get both happening from one source?

54 Chevy Pickup

That's worth a try. I'm not sure it will work though.

McDeuce 04-01-2004 09:41 PM

I'm in the middle of some of this myself, so here is my $0.02.

I don't think hooking up your fan temp sensor to your gauge sensor will work because I think your gauge sensor would be sending varying voltage to your gauge depending on temp so the gauge's needle would move.

Your fan temp sensor is more of a switch (on / off).

You may want to try buying an adjustable thermostat ($17 or so at AutoZone) and having that control your fan. You can either run the fan power straight to the thermostat and use that as the power switch (the wiring scheme that came with in the package), or wire in a relay and use the adjustable thermostat as a switch for the relay (what I did since I have a Haywire wiring system that came with a fan relay). An adjustable thermostat will let you control exactly when your fan comes on.

You can put the temp sensor in your radiator's cooling fins or on the motor side of the radiator.

horvath 04-02-2004 01:15 PM

Thanks, McDeuce -- that's great info.

I just found out the difference between my gauge's temp SENDER and the radiator's temp SENSOR ... and you're right; the sensor is a switch and wouldn't be any use to my gauge.

I'm gonna look into that adjustable thermostat, for sure.

I talked to my mechanic (installed the radiator, etc.) and he said he chose the 190/170 thermostat-switch because of my AC; you don't want the AC consensor getting too hot, he says.

He mentioned that I have a binary something-or-other and if I had a trinary thingy it would turn the fan on when the condensor got hot ... since I don't, he thought it best to run my engine a little cooler.

I said, "Doesn't a 350 sbc run best and most efficient at around 200 degrees?" He said, "No -- the newer computerized engines do, but not your setup."

I need to educate myself further on ALL these points!

54 Chevy Pickup

trees 04-04-2004 06:19 PM

Alan, a couple of thoughts: the purpose of the binary switch (a pressure switch) is to protect your compressor if the coolant level gets too low. The trinary switch has a second pole on the activated side to tell the cooling fan to run as long as the A/C compressor is commanded on. Wiring in a trinary switch, manual switch, and an engine coolant switch becomes a complex circuit, but is optimum. While your mechanic may be much more knowledgable than I, I do not agree that you want your carbed motor running cooler. It is also more efficient at higher temps. The max operating temps is determined by the lubricating media ie oil and the boiling point of your coolant. Our cooling systems are pressurized to increase the coolant boiling point so we now have the maximum pressure as our temprature limiting denominator. Modern engines are approaching the 22PSI level, but I will not go above 17 on my motors because weak points such as head gaskets, radiator tank seams, heater cores etc may not handle the higher pressure levels. Does not Walker provide a sensor bunge at the bottom of your rad? Many fan installation instructions suggest removing the drain coc for your fan sensor since you are dealing with your coolant temp. Now your fan would come on/go off when the coolant system temp is at its lowest (bottom of the rad)

Regardless, sounds like your fan sensor is not responding correctly on the low side.

302 Z28 04-04-2004 07:33 PM

I also believe your engine will be much happier at 190. I would go with the trinary switch if I were in your shoes.


horvath 04-04-2004 09:08 PM

I agree with you both ... I do NOT like my engine spending most of it's time below 180* as it is presently doing. I'd be happy to see my fan kick in at 190* and shut off at 180* ... in fact I won't rest until I get things running just that way.

Thanks Trees, for your usual insight and knowledge. Hey - if my mechanic was so "knowledgable" how come he didn't wire me up for optimum performance? Mechanics are great when it comes to stuff that's too big for me to handle, but I always comb through everything they did with a fine-toothed comb -- and rightly so! This guy did a good job with my radiator install, but I'm convinced that he does NOT like doing any kind of electrical work -- that circuit breaker he installed was grounding out, to a degree, and he just ignored it. I didn't ... after wiring my truck from scratch, I'm pretty confident in that area, so I took the time to bypass his electrical work, revealing a serious problem and fixed it.

I'm not sure I fully understand the trinary switch, Trees. If it tells my fan to run as long as the compressor is on, is it possible that I'll be running the engine too cool again?


1 - Right now, I'm only running an engine coolant switch -- in the manifold. Would that be better placed elsewhere?

2 - My temp sender (for my gauge) is in the block -- that would be best in the manifold, right?

3 - How do you run a manual switch in harmony with the temp sensor switch and the trinary switch?

4 - Can anyone explain what I have to do to install a trinary switch? Where does it go?

PS - I don't know if my Walker has a sensor bunge at the bottom ... how would I determine if it does, and if it does, what is it for? Is THAT where the temp sensor SHOULD have been installed???

54 Chevy Pickup

bud-23 04-04-2004 11:34 PM

<--------- In this I have a 180 stat and a 180 sensor in the water pump. I also have a 3-way switch (on,off,auto). When the water temp gets to about 185 the fans (have 2 small fans) come on. I always leave the switch on auto so that I don't forget to turn it on. After the engine is shut off the fans will run for about 4 or 5 minutes. Don't ask me about the wiring because I did'nt do it.


Centerline 04-05-2004 05:36 AM

Alan, I'd move the engine temp sensor to the manifold and the fan sensor to the bung on the lower radiator tank. Your Walker should have a bung in lower tank on the engine side. Also change your thermostat for a 180* unit.

I do not agree with running a carbed engine hotter than 180 if at all possible. There are too many variables involved in proper combustion and timing for an electronic or points ignition system to deal with. In a modern engine the computer has the ability to vary these very important settings (fuel/air mixture, timing and others) based on the engine's requirements so it can run more efficiently at a higher temperature. Most non computer engines can't. I believe your mechanic is correct, you shouldn't run your engine any hotter especially with added cooling requirements such as air conditioning.

Just think of how your engine's cooling system works. How hot or cool your engine runs is based on the capability and efficiency of your cooling system but the thermostat regulates all this. If its running too cool then your thermostat isn't regulating the temperature and has failed in the open position. If it runs too hot then either the thermostat has failed closed (or nearly closed), the cooling system has a problem, or there is a mechanical reason inside the engine that is responsible (blown head gasket etc). I think if you change your temp sending unit (buy a new one they aren't expensive) and relocate it to the manifold (should be a bung up by the thermostat housing somewhere) you'll get a more accurate reading.


trees 04-05-2004 06:32 AM

Alan, I have a wiring diagram stored in the computer and will e mail it to you. I'm not good enough to attach it here to share with other members so you can do that. I got this from one of Willys' or Kevin's posts from about 2 years ago.


horvath 04-05-2004 09:00 PM

Thanks, Trees -- I'll post a copy here as soon as I get it.

Centerline -- Thanks for the info, bro'. I took a quick look at the bottom of my radiator (engine side) today (just briefly) and all I saw was the pet**** for draining the rad. I'll take a more serious look tomorrow.

The temp sensor I have in there now, is a 190/170 ... that is, it turns my fan on at 190* and off at 170* ... is that a good choice if it's located at the bottom of the radiator? It's presently installed in the manifold, right next to the thermostat -- that's where I want to move my temp sender (for my temp gauge) which is presently on the driver side of my engine, right by the plugs and headers -- maybe that's why I'm getting lower readings on my gauge??? According to my gauge (which I know isn't a perfect reading at present) the fan comes on at 180* and doesn't shut off until 140*.

I have HEI isystem; 350/350; 4 bbl Edelbrock 600 cfi; headers; mild hyd cam.

54 Chevy Pickup

Centerline 04-06-2004 06:12 AM

Alan, I would move your temp gauge sensor to the location where you're fan sensor is now. This should give you a more accurate reading.

If your radiator doesn't have a bung for a fan thermostat, I would spend the $30 it will take (check here) for an adjustable fan thermostat that will replace your radiator petc0ck. This adjustable switch will allow your fan to come on and go off at whatever coolant temperatures you desire and it's the way most street rods run electric fans.


horvath 04-06-2004 07:12 AM

Trees -- It's a very simple matter for you to attach the web page with all it's info that you emailed me. All you have to do is:

1 - Go to that web page and copy it's address (select it from the top address bar in your web browser by clicking and dragging across it, then when it's selected, press Cntrl + C to copy).

2 - Hit reply to any post and click the http:// button (seen above the message box) ... first prompt is to type your title for the link; second prompt is for the web address -- on THAT one you click in the box and press Cntrl + V to paste the address you copied.

When you're done, it looks like this:
Here's Trees' Link

Centerline -- I'm definitely gonna move my temp gauge sensor to the manifold ... AND buy me an adjustable thermostat! Wow! How cool can you get? I can actually watch the temp gauge and turn the fan on or off, and once it's set at the correct temp, I can forget it -- that is the coolest deal I have seen yet!!

What would I do without you guys? Live in a whole lot more misery is what!

PS -- About the petc0ck -- after I put the new sensor there, how do I drain the radiator?? By removing the sensor??

PSS - Where are you at with your 53 Chevy Pickup, Bro'?

54 Chevy Pickup

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