Marc R. Barker Protects an Old Car's New Engine with a Simple Coolant Level Sensor

Engineer Marc R. Barker has fixed a major oversight in the dashboard of an otherwise perfectly usable vehicle — by adding a missing sensor and warning light for low coolant levels.

"Built for a car which never had one. The owner has just paid out for a new engine and he wants to protect his investment," Barker explains. "[It] uses a spare light position found in the car's existing instrumentation. When the water level is good an immersed probe completes a circuit to ground via the coolant in the pipes. When the level drops the probe is no longer in contact, the circuit is broken and the warning lights up. The probe is located in the highest part of the sealed and pressurized coolant, where the level is checked."

That conductive probe, which serves as a simple binary sensor for whether the coolant is above or below a configurable minimum, is a home-brew affair: a brass rod in a length of silicone tube. A hole was drilled into the coolant system's expansion tank and the silicon tube held in place with epoxy; the brass rod, meanwhile, can be moved up or down in order to adjust the trigger point.

"The build up of pressure in the cooling system does not push the rod out," Barker explains for those who may have been concerned that what he had created was actually a hydraulic cannon, "because the cross sectional area isn't enough force to overcome the friction keeping [it] in place."

More details are available on Barker's Hackaday.io page.