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This is a problem solving Honda replacement cooling fan control unit that @wheelsquad and I schemed up, then built and installed on our Ranchers last year while frequenting a failing forum. I think its safe to say that we both feel like they are pretty cool gizmos! These custom gizmos monitor and digitally display the oil temperature in the sump in realtime and provide the operator with automated controls for fan kick on/kick off temps independently. This fully automated, programmable DIY FCU replaces the stock oil temp sensor and fan control unit on any Honda Utility air/oil cooled ATV without any major modifications. The bike remains functionally stock throughout, so can be returned to stock by removing this custom solution, reinstalling the stock oil temp sensor and plugging the stock parts back in. We set out last year to put our heads together to build a better FCU. Honda FCUs come with many faults that we felt we might correct if we only tried... these are the biggest problems that we have solved with our gizmo: As Honda oil temp sensors age the resistance gradually rises until the FCU no longer responds and the motor overheats. Sometimes the OEM sensor resistance may fail low (shorted) as well, or the sensor wire itself may get shorted out somewhere. This gizmo solves those problems in three ways. Additionally, the operator is alerted of a fault condition immediately. In the event the oil temp sensor ever becomes disconnected or the sensor wire gets broken, this gizmo alerts the operator of the fault immediately. The OEM FCU does not turn the overheat light on until the motor oil is scalded and the motor is being damaged. Sometimes the overheat light never comes on. This gizmo features a programmable over-temp alarm that alerts the operator way before the oil overheats and it also keeps the fan running while in overheating condition until the oil temp drops below a safe temp threshold chosen by the operator. With an OEM FCU we have no idea whether the fan is kicking on and off at proper (sane) oil temperatures or not. This gizmo provides the actual oil temperature in realtime on its digital display and features a Red LED that lights up while the fan motor is running, so the operator is always aware of its functions. This gizmo is very fast and is extremely accurate. The oil temp sensor thermie is rated for operation up to 150 degrees C, its published resistance curve is precise and it is rated to within 0.1 degree C tolerance. The display accuracy is rated to 0.1 C as well. I am currently building one of these units for one of @Fishfiles 450 Foremans, which is intended to fully automate the operation of two cooling fans. Before we get started on this project though, lets take some time to explain a bit more about this gizmo and how it works. I am including links to part numbers that I use to build these for those who wish to build their own toys. Please feel free to offer your own ideas on how we may improve on these fun lil' gizmos. 🙂 Alright, lets get started with a bit of show and tell. This is the display & control unit of the gizmo that I built for my Creamsicle. The fan was set to kick on at 100 C oil temp and kick back off at 85 C oil temp at the time these photos were taken on this ravine top last summer: Each gizmo consists of a custom oil temp sensor made by embedding a 10k ohms precision thermistor into gutted out OEM sensor brass. The fan control relays and a custom made regulated DC power supply (for the display) are contained inside a sealed, submersible project box. The gizmo is 100% sealed to be fully submersible and can be shot directly with a pressure washer as often as ya wish. And you can mount the two main components anywhere on the ATV that ya wish, using any mounting methods that ya wish! Lets go over the display parts, functions and control features in the next post eh.

I am making a selectable gizmo for @Vintage Motors 2003 Rancher 350. As soon as I get this project done I intend to make one for @MoeBwonKinobi as well. So since I cannot find an old thread here showing how I make them, this will be a howto thread of sorts. I'll try to document part numbers of components required best that I can. This controller idea stemmed from @jeepwm69's information, his 2wd/4wd Selectable Front Diff using OEM parts thread is linked here. Everything required for the conversion is in Jeep's thread: Here are some pics of a completed controller I made in the past: This is rant about the "why for?".... I'm just pasting this from an old file I found on my laptop: