Force radiator fan to cool transmission cooler

[Kozmob]

After some classic transmission issues, I had a transmission cooler installed on my ’99 EVC. According to my ScanGauge, the cooler doesn’t always keep the ATF cool. I travel a lot on Forest Service type roads - slow and steep – and the temp gets high; at times over 220. Slowing down doesn’t seem to help; I’m already going less than 25 mph; too slow apparently for airflow to cool the cooler.

I’ve tried running the AC to force the cooling fan to operate. The effect was minimal. I think the AC runs the low speed fan.

I’m considering adding a bypass switch to control the radiator cooling fan so it can be forced to operate when needed at low vehicle speeds. I would put something like a 10-minute timer on the switch to make sure it turns off. I would like to do a simple install at first just to test the concept. It seems like the easiest way would be to tap into the radiator temperature sensor switch on the side of the radiator, but I’m concerned that would confuse or damage the ECU.

Anybody here tried this? Any thoughts if I’m on the right track and/or ideas how to better do this?

Thanks / Kozmo

On a side note, going downhill doesn’t seem to result in cooler ATF. Is that because the transmission is still working; braking rather than powering the rig?

[Joshwa]

I think a basic relay that jumps the power across the radiator sensor would work. Then easy enough to pull wire back to a switch on the dash to activate.
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93 Weekender TDI conversion (AHU)
93 MV TDI conversion (1Z)
Weekender rear cot
Late model cabin air filter on 93
Euro spec bumper install on 93

[VolksVelo]

220° F + should still well within the safe operating range.

[Kozmob]

[mikemtnbike]

You could do this. Like 25 years ago I bypassed the relays in a 84 Wolfsburg rabbit convertible (great car) to a dash switch. I don’t remember all the details but I direct wired it to the battery with an inline fuse. Probably not the right way to do it but it worked for years and the factory system still worked too. I lived in phoenix and commuted in the car and wanted control.

Anyway, just saying, sure this is possible.
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1991 Vanagon GL 2.1 AT Westfauxlia. "Frankie" Totaled https://www.thesamba.com/vw/forum/viewtopic.php?t=764510&highlight=carnage
1995 Eurovan Camper "Marzivan"
2020 GTI SE manual

[subdewd]

Yes, did this

[almond]

Do you have the transmission in D or in 2 when its getting that hot going 25 mph?

[Kozmob]

[Kozmob]

[almond]

I thought the transmission was designed to lock in some way if you put it in a lower gear and not make as much heat vs leaving it in D. Page 85/86 of the manual kinda talks about changing the gear selector based on conditions. Maybe if you go into 2 before it overheats, it wont

[EuroTec]

Depending on how close the cooler is mounted to the AC condenser, it will have a hard time exchanging heat to the air when not moving.

Have you verified that you have enough transmission fluid after the cooler install? Might be a bit low for the extra volume needed.

Just a thought...

You could simply bypass the trigger wire from the cooling fan temperature switch to a switch mounted on the dash. Turn on the fan whenever you want.
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If it ain't broke, don't fix it!

[Kozmob]

[subdewd]

It seems to help. Might just be placebo effect. But I use it preemptively in slow traffic or waiting.in line