How to ad bypass switch for cooling fan?

Rcooper · Post by **Rcooper** » 23 Jun 2025, 12:16

Looking to ad a bypass switch to turn on cooling fan for those days when sitting in traffic. No A/C on .Is that a way to run fan without out having ECM turning fan on.This is for 1998 S70.Would like to ad switch without messing anything up.See if anyone has come up with a way to do this.

xanthefin · Post by **xanthefin** » 23 Jun 2025, 12:30

Rcooper wrote: ↑23 Jun 2025, 12:16 Looking to ad a bypass switch to turn on cooling fan for those days when sitting in traffic. No A/C on .Is that a way to run fan without out having ECM turning fan on.This is for 1998 S70.Would like to ad switch without messing anything up.See if anyone has come up with a way to do this.

Do same what ECM does so just ground the fan 1/2 speed or full speed relay through the button.

Rcooper · Post by **Rcooper** » 23 Jun 2025, 13:15

Will I need to ad a diode so it not feeding back to the ECM?

Vova585 · Post by **Vova585** » 23 Jun 2025, 13:28

Can I ask a question. How old is your radiator? When the last time you removed your radiator and washed all the bugs and dirt away? I think it will give you better improvement in airflow rather than adding more switches. Another question: you are in Colorado. Should it make a better sense to add axillary transmission cooler?

Rcooper · Post by **Rcooper** » 23 Jun 2025, 13:43

Radiator was just replaced.Just want to have the option to turn fan on if needed.

Rcooper · Post by **Rcooper** » 23 Jun 2025, 13:47

Yes in Colorado.
With construction holdups and the hot temperatures ,Would like the fan on more.

Rcooper · Post by **Rcooper** » 23 Jun 2025, 13:47

Which cooler would you recommend?

Vova585 · Post by **Vova585** » 24 Jun 2025, 08:09

In terms of added cooler- it all depends on your budget. I remember IPD was making something fancy for around $400 which was plug and play into the existing lines. Some people were cutting in extra cooler in line(but for the life if me I could not think about good location with airflow outside the radiator opening where they could put it.

Post by **abscate** » 24 Jun 2025, 22:58

Rcooper wrote: ↑23 Jun 2025, 13:47 Yes in Colorado.
With construction holdups and the hot temperatures ,Would like the fan on more.

Volvo has designed it to come on when needed. It will run fine at 90c , then kick on at 105C in standstill traffic until the coolant temperature comes back to 90c. There is no reason to run it continuously

Price out a new cooling fan before you think about running it continuously, too.

dikidera · Post by **dikidera** » 25 Jun 2025, 06:16

abscate wrote: ↑24 Jun 2025, 22:58
Rcooper wrote: ↑23 Jun 2025, 13:47 Yes in Colorado.
With construction holdups and the hot temperatures ,Would like the fan on more.
Volvo has designed it to come on when needed. It will run fine at 90c , then kick on at 105C in standstill traffic until the coolant temperature comes back to 90c. There is no reason to run it continuously

Price out a new cooling fan before you think about running it continuously, too.

Thing is, it wasn't designed well. Bear in mind, Sweden has lower temps, maybe sitting in traffic rarely makes it cross 100c, but in other hot regions where ambient temps go to 35-40c, it absolutely does. And it's 105c for emissions, and the reason it goes to 105c quite often is that the idle cooling capacity(pump flow whatever) is not adequate, even @vtl will say so.

Potential solutions are not just a new and bigger radiator(bigger core, depth whatever) but a slight ECM tune to make it come on at say 100c or 95c, buuuut, then you have the thermostat which is designed to fully open at 105c.

I've even thought of adding one of those fancy electric external water pumps some cars have which will turn on at say idle speed