Carb cooling fan aftermarket relay solutions

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Jun 13, 2017
Aledo TX

1) Create a reliable carb cooling relay that operates like the factory one using off the shelf parts since original parts are hard to find or not reliable.

2) Add a bypass feature that cools off the engine bay when running and when the truck is turned off.

3) Use Toyota parts to max extent as possible.

Here is the schematic that so far works flawlessly on my truck.

The first relay on the left is Hella timed delay off relay p/n 996152131. The trigger is the ignition switch, the constant battery (so the fan can run when engine is off) is the tail fuse. The temp sensor is an OEM Toyota manifold temp sensor from another Land Cruiser and connects the timed relay to ground...which is important later.

With the relay “triggered” it powers pin 87 which then provides power to the next 5 pin relay with pin 87 (normally open) and pin 87A (normally closed and defaults connected to pin 30).

If this relay is triggered, it connects to the bypass feature I designed. If it is not triggered (ignition switch off, but still energized by the delay off timer relay) then it powers the default AUTO feature I have. The switch is a modified wiper switch with three positions: OFF, AUTO, and BYPASS.

The AUTO goes from pin 87A to the trigger for a standard 4 pin relay that connects directly to the tail fuse and powers the two fans I’m installing. One is an OEM carb cooling fan. The other is a fan I bought that fits nicely over the vent area. The carb fan blows cold air in, the aftermarket fan sucks hot air out.

Of note, to be able to test the circuits, I installed a bypass of the temp gauge that was the wiper motor function previously. Also, to allow the bypass feature to work properly and not interfere with the auto feature, I installed a diode to keep the electrons flowing the correct way.

As such, the AUTO position allows the timed delay off feature to work when I turn the key off AND the temp sensor is grounded.

When in BYPASS, the system works as the AUTO feature does when key is turned off, but additionally, when the engine is operating AND the temp sensor grounds, the fans will run continuously until the temps cool down. I created this feature so that if I’m in traffic, or it’s hot, or I’m idling, the fans will help cool off the engine bay.

If you need, I can diagram how to modify the wiper switch.






Nice job!

My solution -> click here <-

And after about 5 years & 15,000 miles, it still works as intended. Was working today in the Georgia heat, and went off about 20 minutes after I got home from work. Mine works totally off engine heat, but I do have a shut off switch wired in should it go hay-wire.

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