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Running the 5 wires from the passenger side under the dash to the driver side was really slow and no fun, and the factory intake manifold mounting holes didn’t work for the thermo sensor mounting bracket because the manifold spring was in the way of the sensor, so I made an extension plate and moved the mounting bracket 2 inches towards the firewall and got the sensor to within 1.5 inches of touching the manifold:
Finally, got everything connected - - Fire in the Hole!
Turn the ignition on, start engine, drive 20 minutes, shut off engine and… no fan. WTF!
Thus began a month long search for the problem, interrupted by life stuff. I wasn’t at all sure the thermo sensor worked, so I ran the hot oil resistance test and measured resistance of 50K ohms at room temp, dropping to 2K ohms at 275*. I think that means it works, yah?
Finally, after enough troubleshooting to last a lifetime the culprit turned out to be a measly ground connection from the fan to the fender – hard to trace but easy fix. And that did it – I now have a fully functional carb cooling fan installed in my 77 Federal FJ40, just in time for winter!
Most of the info I found in my Mud searches did not come from Toyota. In fact, they provided a paucity of it in their body of workshop literature. Nope, our Mud family was where I found the most useful info, from your own experiences. Even a few electrical engineers chipped in. Thanks to you all.
Based on what I gleaned from my readings, in my humble opinion the thermo sensor is the be all and end all of this system. When the engine is cold, sensor resistance is high and the electrical circuit is closed.
The controller/relay/timer is programmed to open the fan circuit when a running engine is turned off, but only if sensor resistance has fallen to the 2K – 3.8K ohms range (engine temp 194 – 230*F). So if the engine temp has not risen to this temp range the fan will not turn on when the engine is shut off (sensor override).
The timer can only do two things – 1) run until the sensor signals it to shut off or 2) time out at 30 minutes if it’s received no signal from the sensor. The timer is programmed to run from 20 – 30 minutes, but if the engine temp is just barely hot enough to get the sensor to trigger the fan, the timer will be shut off as soon as engine has cooled enough to get the sensor to trigger the timer to shut off (as soon as 8 minutes in my case). Read that last sentence a couple more times and it’ll start to make sense.
Before I started this project, troubleshooting a dysfunctional horn system had held the record as the most ornery, torturously frustrating FJ40 repair project I’d done, but this one proved worse BY FAR. And now that it’s done, every time I shut off the engine and hear that fan I say to myself Hell yeah, I’d do it again in a heartbeat!
Finally, a huge shout out to Nate and Russ – no way I could have done it without your knowledge, experience and especially your patience as I clod - hoppered my way to the finish line. THANK YOU
I now turn this Mud seminar over to the Questions and Discussion workshop. No Mud slinging, please!
Finally, got everything connected - - Fire in the Hole!
Turn the ignition on, start engine, drive 20 minutes, shut off engine and… no fan. WTF!
Thus began a month long search for the problem, interrupted by life stuff. I wasn’t at all sure the thermo sensor worked, so I ran the hot oil resistance test and measured resistance of 50K ohms at room temp, dropping to 2K ohms at 275*. I think that means it works, yah?
Finally, after enough troubleshooting to last a lifetime the culprit turned out to be a measly ground connection from the fan to the fender – hard to trace but easy fix. And that did it – I now have a fully functional carb cooling fan installed in my 77 Federal FJ40, just in time for winter!
What I learned
Most of the info I found in my Mud searches did not come from Toyota. In fact, they provided a paucity of it in their body of workshop literature. Nope, our Mud family was where I found the most useful info, from your own experiences. Even a few electrical engineers chipped in. Thanks to you all.
Thermo sensor
Based on what I gleaned from my readings, in my humble opinion the thermo sensor is the be all and end all of this system. When the engine is cold, sensor resistance is high and the electrical circuit is closed.
Controller/relay
The controller/relay/timer is programmed to open the fan circuit when a running engine is turned off, but only if sensor resistance has fallen to the 2K – 3.8K ohms range (engine temp 194 – 230*F). So if the engine temp has not risen to this temp range the fan will not turn on when the engine is shut off (sensor override).
Timer
The timer can only do two things – 1) run until the sensor signals it to shut off or 2) time out at 30 minutes if it’s received no signal from the sensor. The timer is programmed to run from 20 – 30 minutes, but if the engine temp is just barely hot enough to get the sensor to trigger the fan, the timer will be shut off as soon as engine has cooled enough to get the sensor to trigger the timer to shut off (as soon as 8 minutes in my case). Read that last sentence a couple more times and it’ll start to make sense.
Conclusion
Before I started this project, troubleshooting a dysfunctional horn system had held the record as the most ornery, torturously frustrating FJ40 repair project I’d done, but this one proved worse BY FAR. And now that it’s done, every time I shut off the engine and hear that fan I say to myself Hell yeah, I’d do it again in a heartbeat!
Finally, a huge shout out to Nate and Russ – no way I could have done it without your knowledge, experience and especially your patience as I clod - hoppered my way to the finish line. THANK YOU
I now turn this Mud seminar over to the Questions and Discussion workshop. No Mud slinging, please!
