I would like to install a 16" puller fan and dump the engine fan. Engine is a mild SBC 350/350 with no AC. Three row aluminum radiator and a 180 Stat. This will be the wiring application used. What would be the ideal temp on/off sensor? 185-on 175-off good enough or higher?
It should be a fair bit higher than the thermostat opening temperature, so maybe 190 to 200. I would add a manual override switch as well, as suggested by Manyolcars. I like to turn on the fan a minute or two before I get to my destination, so the radiator and hoses aren't left boiling hot when I park. I figure it should help them last longer.
I would run a relay in that schematic as the thermoswitch (thermostat in your drawing) probably isn't rated for the amp draw of the fan. As for the temps, see what the engine likes as far as cruising temps go, and set it to turn off slightly higher than that so the fan isn't running as you're cruising down the highway. Turn it on 10-15 degrees above that. I typically set them up at 205-on, 190-off.
The rating listed on the thermostat is the point at which the device begins to open. This is not the full open temperature, which is typically 15-20 degrees above the listed temp. For example, a 180 degree thermostat begins to open within three degrees of 180, so 177 to 183. It should be fully open at around 200. Your fan should come on at a bit higher than the 200 mark, and turn off a little under the 200 mark. With a 180 degree thermostat, I would set it up for 210 on and 195 off.
On my Chev 350/350 combo, I run a thermo-switch out of a mid 80s Mitsubishi car radiator, the Mitsi radiator has plastic top and bottom tanks, but the sender screws into a captured brass fitting in the lower tank.. I cut the plastic, removed the fitting, and soldered it into my brass bottom tank (I mounted it in the lower tank in approximately the same position as the factory did, from memory close to the lower radiator hose outlet.. Wired 12v thru the primary side of the relay to thermo switch/earth, and slightly heavier wire thru the secondary side of the relay switch to the the fan, both are constant 12v power.. The fan kicks in as required temperature wise, and when parking up, the fan continues to run until coolant temp lowers below the thermo switch setting, which then turns off the fan.. Been like this for 20 years, and still working fine..
I have one of these , 22 years , 40a relay , 30a fuse , 16" fan . A 30a relay won't last long , nor will a 20a fuse . The control won't last long without a relay carrying the load .
The start up amp draw will be more than the "running" draw. A 30 amp fuse would be my choice, as 2OLD2FAST suggests.
I would definitely use something other than a 20 amp fuse. If you still decide to go that route look at maxi-fuses. I think they go up to around 120 amps.
I installed an electric fan in my flathead roadster and in my 442, both housed in fan shrouds. The flathead has a 180 in the radiator, the 442 has a 190 in the intake. Both have override switches inside the car just in case. Both run nice and cool. The Olds has 2 fans side by side and the controller I used can start one or both depending on the situation/need. The roadster is a Spal and is on or off. When it comes on it pulls a bit of juice. I have it on a relay and a 30 amp fuse. On a hot afternoon at PIR, I turned off the olds and hit the fan switch to cool it in the pits. Forgot about it and battery was dead when I went back to stage for the next run. They suck a lot of...well they just suck! Not crazy about using them.
The fuse size is not based on the fan draw. The wire size needs to be able to handle the fan startup draw without melting. The fuse is sized to protect the wire from melting if there is a short, nothing more.
Where will the temp sensor for the fan be located? I have mine in the lower tank like @inthweedz does. I have a 180 stat and set the sensor to 195. Lower tank has the advantage of when going down the road the ram air lowers the coolant temp at the lower hose (tank) so the sensor keeps the fab off.
Then 20-30 above thermostat setting, pretty much what all car manufacturers have been doing since the 80s when electric fans took off. I have two Spal 12" fans wired in 2 stages. Low stage connects them in series (6 volts each), high connects them in parallel (12volts each). I know you said you have 1 fan, but if you find the need for 2 this works flawlessly. Very quiet on low speed. I put in a universal 12v timer to keep the fans on at low speed for 4 min when the engine is shut off. Really helps with underhood temps with the FE stuffed in there. This is my drawing so I could understand it. This is out of the book that came with my controller. Where I put the 3 relays. Highly recommend this controller. These universal timers work well for anything automotive, off delay, on delay, flasher, wiper delay, whatever.
The comments above are really good. You might also take a look at the flex a lite controllers. I’ve had a couple builds where I had no choice, the belt drives for the McCulloch superchargers took up all the clearance. I like the soft/slow start and adjustable temp setting all in one package. Delayed shut off, etc. Like the HPC combo above. https://flex-a-lite.com/accessories/electric-fan-controllers.html?product_list_limit=15
Well you put thought and time in your application and I'm sure others are seeing this as well. My project is nothing, you have done your fans well. I am happy to see your timer is American made.
I wouldn't put the sensor in the intake. That water is hot all the time once the engine is up to operating temp. Think about it for a sec and you'll understand. You want the fans turning on when the water exiting the radiator gets too hot, IE the air passing through the radiator isn't cooling the water sufficiently, hence the fans turn on. Done this way, the fans will turn off when sufficient air is passing through the radiator to cool the water (going down the highway for example) and turn back on when there isn't (exit freeway and come to a stop). The coolant exiting the engine (intake manifold location) is always hot once operating temp s reached. You want to monitor the temp of the water coming out of the radiator as that will tell the fans whether they need to kick in and help out or not.
At the same time, the coolant returning from the radiator may be cold despite the coolant coming out of the engine is actually boiling. You'd really want the fan to kick on then. As far as i know, the normal place to check temperature is the coolant exiting the engine. If that's too hot you need to send cooler coolant back into the engine, and the sensor should be chosen so it only starts the fan when the temperature is about to be too high, not just hot. Hot is normal for a running engine.
If the coolant coming out of the rad is cold when the engine is boiling, then it isn't a cooling problem. It would be a circulation problem. FWIW, my temp sensor location in in yhe drain port for the radiator, and it doesn't work nearly as well as I had hoped. Seems to just turn the fans on whenever the thermostat opens. I've got a leaking water pump so I'll be pulling the radiator, at which time I'm going to weld in a bung in the top tank. I think a crossflow radiator would work better for the sensor being in the outlet tank.
Your project isn't nothing, I just want to help it work as well as it can for you. I've worked on a lot of cars, and want your project to function as well as it can.
I have a temp sensor switch in the right side cylinder head. Many don't like that, but I find it turns the fan on only when idling in traffic on a hot day. The fan is able to lower the temp at that sensor almost immediately with the car not moving. Switches fan off once you drive for a minute. Isn't this the kind of cooling performance that we are all trying to achieve?
I moved this to the main board, the traditional hotrod forum is no place for a discussion on electric fans
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