Old dog needs new tricks

Old cars normally die due to overheating problems. Some times it's the fan that gets stuck or the sensor that stops sending data properly, then you stop at a red light and don't mind the needle going up till the red, and then it's too late and you've burn the head-gasket.

The the majority happens with overheating for lack of water.

Out of these a good percentage of cases is attributed water circuit purely falling apart from cracks on tubes and vaporizing or dumping the water out. Other times the car has overheated before the owner understood it had a cooling issue, and the burnt gasket allows water to combustion passage, and the car will consume water, only noticeable if it is enough to cause compression and detonation issues.

All my cars are old, and with this trend of building worse cars, I'll keep having old cars.

So the first thing I do is to setup an alarm system for the water lever in the expansion tank.

Some cars have an embedded solution for this, others don't as making you replace the engine or buy a new car, is preferable to allowing you some quality for your money.

So on my 2 Hondas, 2 Fords and a Volvo made by Ford, I decided to add a water level warning system... the old 1997 Volvo v70t5 has this from factory... a true sign of times. It's clear to me that somewhere in 1997, engineered ruled and the economists where tied down in a closed room, without windows, down in the basement.. but then someone forgot to lock the door and they got out.. and then they over-thrown the engineers and it has been getting worse by the year.

Shopping list:

5v trigger 12v operation relay module like this:

https://amzn.eu/d/cySr42T  5V trigger is important as some relay modules are 12v operated, and the sensor does not send 12v to trigger the relay. Be careful with this.

led with buzzer alarm 12v:

https://amzn.eu/d/apxafaF

liquid sensor (external):

https://amzn.eu/d/hlVArrI

The schematics:

Explaining:

You will need to wire the sensor and the relay module to a 12v power source. Obviously this circuit doesn't make sense without the engine running, so I recommend you look for the fuse connector that is switched by ignition. That way, your circuit will only draw power with ignition on.

Next you need to ground the GND and (-) connectors for the same devices. That is Sensor, Relay and LED.

Now comes the interesting part. Since you want this circuit to default to trigger mode (in case something fails), so the power to the led should be set as DEFAULT on the relay as pictured. In essence, as you power or the circuit, you should hear a short beep then the triggering of the relay and silence.. until sensor stops sending level data, or the circuit fails for some reason. 

Finally connect the sensor trigger to the relay trigger and test the circuit.

The last part is using T-Rex to glue the sensor to the expansion tank.

Use a lower placement of the sensor and  remember that water will be jumping around that reservoir, while you drive... avoid areas that could get dry on hard cornering.

On my Puma, it looks just like this:

So now, If water runs too low. because of anything and old car can manage to break to do this, starting with a rotten radiator, or dried and fissured rubber hoses... maybe even a gasket starting to go... the red light, together with a buzzer will start sounding. 

You can stop the car before you really burn the gasket and make a mess out of things.