Coolant level indicator with your own hands

Coolant level indicator with your own hands

While most cars have a temperature gauge to alert you to overheating, they do not alert you to a leak in time to prevent potential engine damage. Today I’m going to show you how to know when your car is losing coolant by installing a coolant level indicator in the tank.

The idea is that the coolant reservoir (tank) will empty before the radiator does. While driving, an empty reservoir is a good indicator of a problem. And I also want to say right away, or rather boast that I recently purchased an original key for the car, now I experience joy every time I start the car.

Coolant loss can be the result of any malfunction, including a problem with the water pump, a leaking gasket, or a cracked hose. We are not looking at the cause of the leak here .

Coolant level indicator with your own hands

The indicator has two LEDs. The green LED blinks when there is liquid in the tank. Otherwise if the level is low or empty the red LED blinks. By selecting the correct fuse in your car, we will ensure that the indicator light will only turn on when the car is running or the key is in the “ON” position.


The indicator is based on a microcontroller and includes built-in hardware features called “sleep mode” and “watchdog” i.e. it will periodically “wake up”, take a reading, flash the corresponding LED, and return to “sleep”. Thus, this is the most efficient power consumption mode, as compared to constant switching on.

Coolant level indicator with your own hands

Printed circuit boards can be made by printing on a laser printer, then transferring the tracks to the copper with a laminator

6 7


The software is written in JAL, so you will have to download the JAL compiler if you want to change the code.

The device is built on a PIC16F88. Download the lowcoolant.hex and use the PIC programmer.

Digital tachometer on a microcontroller

The program has a sleep mode and a watchdog to efficiently monitor the coolant level every 2 or 3 seconds.


The board is connected with several wires. 1 wire is connected to the fuse, which receives voltage when the key is in the “ON” position or the engine is running. Through this wire comes 12 volts from the car battery. The ground wire on the board is connected to the ground on the car.

Coolant level indicator with your own hands

The car ground is any exposed metal connected to the car chassis. The other 2 wires supply voltage and provide the ground of the 2 LEDs. Finally, the 2 thicker wires come from the coolant sensor.

On my 99-Ford Explorer, I connected to fuse #12 on the inside fuse panel that is used for the wiper pump.


To find which fuse to use, unplug the fuses. Connect the black voltmeter probe to the car ground and the red one to one of the two pins of the fuse socket. If it reads voltage (not 0), try another fuse. If it reads 0 volts, place the red probe on the other pin.

If it reads voltage, try another fuse again. We are looking for a fuse that is not energized when the key is in the “OFF” position.


Now turn the key to the “ON” position as if you were listening to the radio. Now we have to find out which of the two pins of this fuse socket is energized.

We will use the pin that is not live (use the one with 0 volts). This will ensure that 12 volts are coming to the board when we put the fuse in, and if something is wrong, the fuse will blow. I used a thin wire, sandwiched it between the fuse and the 0 volt contact slot.

Next, I connected the ground and wires from the LED board. I routed the coolant sensor wires so that I didn’t have to drill any holes. Placed them in the tank and ran them through the engine compartment, making sure they didn’t touch any hot parts. I hid the circuit board in the console, placed the LEDs over it, and proceeded to test.

Simple voltmeter for car on microcontroller

Coolant level indicator with your own hands

Testing and Troubleshooting

To test the LED, the key must first be off. The LEDs should not be flashing. If the LED is flashing, select another fuse that is not energized when the key is in ” OFF “. Now insert the key and turn it to “ON”. The green LED should be flashing (the sensor is immersed in liquid). If nothing happens, check if voltage is coming through the selected fuse. Check the contact to ground. Check the LED connections and their polarity.


If the red LED is flashing, lift the probe out of the coolant. If the green LED now starts flashing, you have mixed up the LEDs. If the red LED keeps flashing, there is a short in the probe. If the green LED blinks now too, then there is not enough voltage being measured when the probe is immersed in the coolant, you should short the probe wire ends more.

12 Coolant level indicator with your own hands

If that doesn’t help, try pushing the probe wire ends closer together. Finally, you can try reducing the WETNESSTHRESHOLD constant in the lowcoolant.jal program (you will have to recompile), or increase the 1 mOhm resistor rating.

Over time, this may also be required for old coolant, which oxidizes and becomes corrosive, thus limiting the ability of the probe. In that case, the indicator will flash red when immersed in coolant, and warn you that it’s time to replace it before your engine suffers from corrosion.

Of course, this troubleshooting guide assumes a fully functional circuit board, so you should check the connections on the circuit board and the quality of the soldering if you haven’t done so before.

Antifreeze and washer fluid level sensors.

Hi all. With the onset of the “muddy-slush” season washer fluid is washed much more and it is not unreasonable to make control over its amount, so that “surprise” about its completion is not caught somewhere in the road. It is not superfluous also will be and control of coolant level, and maybe even more important, as with a dirty glass you can still get there, but without the right level of antifreeze already can affect the work of the engine and you can not get there). First the sensors from the injector family and the warning lights were purchased

Automatic door closer connected to the alarm system

and planned to implement them in the already installed tanks, but after thinking about the efforts in the normal, without further depressurization of the sensor mountings, as well as the future problem-free replacement of failed parts, decided to abandon this idea and make everything as simple as possible with possible breakdowns, even the quality of new parts leaves much to be desired. The easiest option is to immediately install the tanks from these gauges, with the transfer of their mounts. The 08i expansion tank is excellent for this purpose,

especially if 21214m GTS is installed and original tank had to be crumpled with a construction dryer. For fastening the stock mount stays in place, only removes external tank mounting bracket, the 08 tank decided not to fasten “hard” such a plate, for quicker replacement and convenience, fastened it with the rubber mount from the 05.

With two of these straps, moved two hooks to one, on both sides. One side is fastened to the side member, the other in the hole made in the stretch.

Held very well.

Expansion cap took the Euro-Detail, many do not like its quality, but since the classics a little different design of the expansion system, will fit with the remake just right. The lid dismantled and “experimentally” by cutting off one coil of spring, found the desired force on the valve.

Now when the fluid expands, the valve does not interfere and works as it should, skipping unnecessary extra pressure. The washer tank is also 08,

(before there was a 6L of 21214 and I haven’t been tuned for less). For ease of use just put connectors on the pump

For ease of use I installed connectors to the pumps, much more convenient than just terminals in heat shrink tubing.

Check valves were already standing and working properly.

After trying the tank decided to move its fixture. I bought a cistern bracket for it, and made a plate for it out of 4mm metal.

Tachometer Light Cutoff or Shift-Light

Old bracket has not removed yet,

In summer will be made vinyl under the hood and added another tank for the headlight washer, then will be finalized and all unnecessary things will be removed and ennobled. I fixed the new mount with self tapping screws. The bottom part of the tank rests on an additional retaining bar from the old 21214 tank, eliminating cracks in the tank itself, as it was before the retaining bar was installed.

Signal lamps were glued temporarily on the panel,

Just in advance added another red light, under the oil level sensor in the crankcase, with the oil change will be and its installation. Type of “beard” also not final and will be remade over time. Wiring is simple, one sensor connector pin is connected to the common ground, the second to the indicator light connector. The second signal lamp connector connects to the plus fuse, which gets power after the ignition is turned on. Everything works great and the right moment with the level is now always in view.

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