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by londons_explore 944 days ago
It's also a common cause of breakdowns... The fan normally cools the radiator, but the temperature sensor is on a coolant hose. Since the engine is stopped coolant isn't flowing so the fan isn't cooling the same thing the sensor is sensing, which means it can end up running for 30 mins or more. Since the fan can be 20 amps or so, you can easily kill old car batteries due to this effect. User comes back after an hour shopping to find their car battery is dead.

If I was a car manufacturer, I would wire the fan into the ignition circuit so it can never run with the ignition off - it's fairly useless to have a fan blowing on a radiator when the coolant isn't flowing anyway.
1 comments
pests 944 days ago
Isn't that feature the exact one being discussed in this threads in order to not overheat the engine though?
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londons_explore 944 days ago
Yes, but other posters are mistaken that it is a 'clever' feature to prevent overheat during heat soak. It is instead more an accidental byproduct of the fact it is wired direct to the battery and not to the ignition circuit. Thats done to save a couple of cents on the ignition switch (no need for a large high current fan to be powered through it).
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epcoa 944 days ago
No you’re mistaken.

> Thats done to save a couple of cents on the ignition switch (no need for a large high current fan to be powered through it).

The fan must be powered by a relay in most cases so this is utter bullshit.

In most any modern car the fan is controlled by the ECM (a computer). Furthermore this fan relay will come on in anticipation of high heat load such as when the AC is turned on as well in cars without dual fans.

There is so much more complexity here than just wiring through the ignition circuit (which wouldn’t cost any more anyway as noted) that thinking this is a cost saving issue is utterly clueless.

And the temperature sensor that controls it is invariably located in the engine block, not the radiator hose. Modern cars may have multiple sensors but they need one in the block.

Cooling fans in most cars don’t draw 20 amps while running normally (they should be closer to 10), and while anything can fail the cooling fan in these setups should only run for a few minutes. Draining the battery like you claim is not a “common” cause of breakdowns.

You clearly don’t know much about modern (last >30 years) cars to be commenting on them so authoritatively, tone down your arrogance.

https://acurazine.com/forums/3g-tl-2004-2008-93/wiring-diagr...

This is a typical setup (and it’s 20 years ago). Debunking two of your claims. First note that the condenser fan is wired through the ignition, debunking the notion that it would be costly to do so and that running the main fan bypassed isn’t intentional. Also note that the actual fan control is the lower right black box PCM/ECM (engine computer)

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