Have you ever been towing a heavy load up a hill and watched your temperature gauge climb? From the factory, the ECM is programmed to engage the clutch in your engine cooling fan to come on at a predetermined temperature. However, that temperature might be higher than you like and once the engine reaches this temperature it can take a while to bring it back to a normal temperature. But what if I told you a coolant bypass switch will give you complete control over the electronic clutch in your cooling fan? This means you can turn on the fan with a flick of a switch.
The coolant bypass switch and harness is an easy plug and play design. Simply make the connections at the coolant temperature sensor with the harnesses OE connectors and run the wire and the switch into the cab of your truck.
I give you the Driven Diesel fan clutch accelerator (override) switch. How it works is, that it tricks the ECM into thinking the engine temperature is higher than it actually is. When the switch is activated, it manipulates the engine coolant temperature reading in order to cause the ECM to fully engage the electronic fan clutch. As a side note, as it does this, it is normal to see the coolant temperature gauge on the dash read between 30 to 40 degrees Fahrenheit higher whenever the switch is turned on.
The coolant sensor on the 6.7 Cummins is under this cover at the front of the engine. Simply move the cover out of the way and connect the Driven Diesel harness to the sensor.
According to Gary Maschner of Driven Diesel, “the most common time you would use the switch would be prior to starting an uphill climb with a heavy load behind the truck. This will engage the fan clutch and help maintain normal operating temperature or keep the system from reaching high temps as quickly as it would if the ECM was making the decision to increase fan RPM. This could be the difference in making it to the top of a climb without an issue or overheating before you reach the top. Also, during summer months it can be used in stop-and-go traffic (or when parked), keeping more airflow through the air conditioning condenser will help provide cold A/C, rather than the fan cycling on/off due to system pressures or temperature.”
I do need to tell you, that if you have a fan that is not functioning correctly, this Driven Diesel switch harness cannot fix a worn-out fan clutch. Operating instructions and expected fan speed changes assume a properly functioning electronic fan clutch.
With the harness plugged in at the sensor (left) the wire can be routed into the cab. The wiring has a protective sheathing around it and it looks OE once properly routed. I made a small hole in the hood-release cable grommet to route the wire from the engine bay to the inside of the cab.
A Few Things To Keep In Mind About The Coolant Bypass Switch
- It is normal for the fan to take some time to react after turning the switch on or off. In my installation, I have seen it take up to 30 seconds for the fan to speed up in my truck.
- It is normal for the fan switch to not cause fan operation if the engine has not warmed up yet. Because the switch increases the ECT reading by 30 to 40 degrees, it is still possible for the ECM to keep the fan speed low if the actual engine temperature isn’t high enough yet.
- If you want to see the actual temperature of the engine coolant on your dash or monitor, you need to have the switch in the OFF position.
- Leaving the switch in the ON position will likely cause a noticeable reduction in fuel economy and will likely make the truck feel sluggish. This is because the working fan will be using horsepower to operate the fan. It will certainly cause more noise from the engine fan as it is locked on. This is not how the product was intended to be used. Only use as needed.
- It is best to leave the switch in the OFF position until needed and turn it back off once it is no longer needed.
Finally, find a place to mount the switch that is within easy reach and will not get kicked or hit which could inadvertently turn on the switch or break it.
This cooling fan bypass switch is a very easy installation, and it took roughly 20 minutes to install it in Project WorkHorse. Just remember to make sure all wires are situated so they do not make contact with any heating source or anything that might chafe or cut the wires. While I did this install on a Cummins Ram, the coolant bypass switch is also available for Power Stroke-powered trucks. If you do a lot of heavy towing or sit in your idling truck for long periods, this cooling fan bypass switch is something to help you and your truck keep your cool.
