Cooling fan sensor; '78 FJ40

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myquestoyota said:
That's what I was thinking but someone had led me to believe that the sensor we are looking at was the smog sensor. I might just have to go looking for that fuse in the cab, maybe that's all I need to have a working fan.
Thanks spot!
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The fuse(5 amp) should be located under the psgr side air duct-next to the firewall(and the fan relay assy)

cooling fan fuse loc.webp


cooling fan fuse and relay.webp
 
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Yes, I was just referring to doing a search, lots of info on this. Gee, didn't mean to sound like a douche, we save that for CHAT. Good luck, there's no place like MUD, there's no place like MUD.......:beer:
 
Thanks for the pics sg, I was thinking it was deeper in the hole than that.
 
Skip; thanks, still working at it, but lots of hours this week-may get back at it this weekend. Any experience drilling out the piece of easyout(I imagine tool steel) with a carbide center drill? If I can get it extracted I should be in great shape. Hope you are right with myquest, no desire to start feuds here, just looking to share what we all seem to have in common; love of the 40's!!! He came off kind of condescending though........
 
myquestoyota said:
Yes, I was just referring to doing a search, lots of info on this. Gee, didn't mean to sound like a douche, we save that for CHAT. Good luck, there's no place like MUD, there's no place like MUD.......:beer:
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myquest; sorry man just seemed kind of like a dig. How did you make out with your sensor challenge? Still working on busted bolt in the side of my intake manifold.........Will try and get pic up
 
fj401978 said:
If you have room, you can sometimes break and easy out up with a punch...it will come out in chips, I've done that before...
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Skip I did think of that but had vacumn leaks and lots of TLC was given to the install of the intake manifold, don't want to create and probs by using a punch. If we didn't love these things would we go thru all of this????????
 
myquest are you anywhere near Seattle or the Olympics? I hear it is really nice country up there.
 
tls3601 said:
myquest are you anywhere near Seattle or the Olympics? I hear it is really nice country up there.
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Yes it is beautiful country. I am perfectly located halfway between Seattle and Portland and halfway between the ocean and the mountains. An hour and a half and I can be anywhere from snow to surf to concerts and entertainment in the big city. Razor clams and oysters to Bavarian villages where the beer and sausage are king. Stop by some time. :beer:
 
sggoat said:
The fuse(5 amp) should be located under the psgr side air duct-next to the firewall(and the fan relay assy)
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I found the fuse, remove the air duct and there it was! It was blown, sure enough. Gave it a good test run to see if the fan would kick on but that new OEM radiator from beno works so good I rarely get above 1/4 on the temp gauge these days. What's the best way to test this out?
 
You can always use a heat gun (carefully) to try and get the fan temp sensor up above 175 degrees. You'd want to be careful not to overdo it or damage anything in the area. With a sensor on top of the intake manifold, as in earlier trucks, it might be difficult to get to temp because of air flow.

With a blown fuse, you might want to open the fan controller and look for damage there. When my '78 fan first stopped operating many, many years ago, I found a foil trace on the pc board inside the fan controller burned. I didn't find any other problems in the controller or the circuit, so I repaired the trace with a short length of wire and the fan has operated properly since then.

Did you mention running the fan directly off the battery already? One of the first things I'd do is verify that the fan runs.


myquestoyota said:
I found the fuse, remove the air duct and there it was! It was blown, sure enough. Gave it a good test run to see if the fan would kick on but that new OEM radiator from beno works so good I rarely get above 1/4 on the temp gauge these days. What's the best way to test this out?
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Yes, the fan does indeed work. The PO had it wired to a switch on the dash. I used that switch for a quick link to my fog lights and now I'd like to get the fan working. But the rig starts so much better with the Trollhole carb installed it's not a priority. Just something I want working. I'll check inside the controller, thanks.
 
spotcruiser said:
You can always use a heat gun (carefully) to try and get the fan temp sensor up above 175 degrees. You'd want to be careful not to overdo it or damage anything in the area. With a sensor on top of the intake manifold, as in earlier trucks, it might be difficult to get to temp because of air flow.

With a blown fuse, you might want to open the fan controller and look for damage there. When my '78 fan first stopped operating many, many years ago, I found a foil trace on the pc board inside the fan controller burned. I didn't find any other problems in the controller or the circuit, so I repaired the trace with a short length of wire and the fan has operated properly since then.

Did you mention running the fan directly off the battery already? One of the first things I'd do is verify that the fan runs.
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The foil/solder trace is something I never thought to check on the controller board. Prob why mine hasn't worked--do you by chance have any pics of the trace and where it's located on the board?
 
It's not a sophisticated board. Just open up the controller and look for any obvious damage.

sggoat said:
The foil/solder trace is something I never thought to check on the controller board. Prob why mine hasn't worked--do you by chance have any pics of the trace and where it's located on the board?
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thanks--
 
spotcruiser said:
Temp sensor mounting is pretty much what you'd think.

You really only need to disconnect your battery negative if you're going to be messing with something that is hot with the ignition off and might touch ground while you're fooling with it/around it, such as a starter cable or the dash cluster (ammeter studs). It's not a bad practice while you're doing any significant work on the truck, though, or if you're welding on the truck.

View attachment 939999
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Hi spot
Do you know what the sensor touches/senses? Is it the intake manifold temperature? Or ambient temperature?
Reason I'm asking is because mine is a non US model and I added an electronic timer set for 20 minutes and a 203 degrees thermoswitch which is sensing the intake manifold temperature (but not sure its correct location/part to sense....)
20210605_230849.webp
All works great but always run for full 20 minutes after a ride (warm engine) and ignition off (so maybe I'm sensing wrong part....intake manifold temperature is very high after a ride).
I was wondering if this behavior is like oem solution....in terms of temperature sensing vs working duration
 
Sensor is not in direct contact with anything. Fan comes in after I shut engine off and typically runs for between 7 and ten minutes on my ‘78
 
tls3601 said:
Sensor is not in direct contact with anything. Fan comes in after I shut engine off and typically runs for between 7 and ten minutes on my ‘78
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Do you know how far the tip of the sensor from the intake manifold? I'm trying to make it as close as possible to the oem solution....thanks
 
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