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MECHANICAL
ECT sensor
Engine Coolant Temperature (ECT) sensor
The main function of the ECT sensor is to ensure the optimal operation of the engine, and at the same time protect the complete cooling system including the interior heating of the passenger compartment too.
From an electronic point of view the ECT sensor is only a temperature-dependent electrical resistor, and mainly its NTC type thermistor - in rare cases PTC - is used in the automotive industry which is basically just a resistor with negative temperature coefficient.
This all just means that as the external temperature rises, the internal ohmic resistance of this NTC thermistor decreases accordingly. So in this way, it can be used reliably in electronics - see picture below - for continuous temperature monitoring tasks, since the actual temperature value can be easily deduced from the value of the resistance due to this clear assignment.
I think so it is pretty easy to find them even for the less experienced drivers, since the ECT sensor is located in most vehicles in the cylinder block near the thermostat housing, or just in the thermostat housing, but of course we can even meet them on the cooling radiator, and often even more of them can be found in the engine compartment too.
So far so good, but how it all works?
The ECT sensor - like the other sensors in the vehicle - receives the standard 5V supply voltage as input, but according to Ohm's law, the voltage measured between its poles is proportional to its internal resistance, which is - as we have clarified a little above - temperature dependent.
So at this point, it should be clear that this sensor can send back signals to the Engine Control Unit only between 0.5 V and 4.5 V, and I don't think I have to say that this crucial temperature information plays an important role in the calculation of the air-fuel mixture. Just think of the well-known fact that more fuel is needed to start a completely cold engine, and an already hot engine no longer needs fuel enrichment.
It follows that there may be such a problematic case that if an engine is difficult to start, then the main reason for this may even be a faulty ECT sensor, as it feels that the engine is already warm when it is still cold. In this case, the Engine Control Unit reduces the amount of fuel in the mixture, which can be seen even on the bleached spark plug electrodes if we unscrew them during an inspection. In addition, I have already seen such an unpleasant case that the incorrect air-fuel mixing error always occurred only at a certain higher temperature point, and as a result this the engine began to tremble unevenly.
So, in case of such symptoms it is always an excellent idea to check the full characteristic - even the resistance - of the ECT sensor by heating the water pretty slowly, and making sure that there is no sharp break somewhere in the characteristic. Anyway, its operation can be checked easily through the OBD serial diagnostics, but can even be inspected with a simple multimeter, since its internal resistance can change from a few K Ohm to a few hundred Ohm.
Anyway, it's worth keeping in mind when replacing the ECT sensor, it is very important to have a proper seal, so it is advisable to lubricate the copper screw thread with silicone grease as well, but in this case the predefined tightening torque must be much lower, otherwise we can easily interrupt its screw thread.
Should I change the coolant?
To make this short article even more compact, I consider it especially important to show why it is advisable to change the coolant regularly.
Of course, servicing the internal combustion engine must not stop at the end of the annual - or recommended 12,000 km - oil change process, which in the case of motorcycles is limited to a few thousand km, as it is sometimes worth thinking about changing the brake fluid and coolant as well, but neither the servo nor the transmission oil should be completely forgotten.
Then let's just look at the engine coolant change.
At first glance, we might think that only 1 hour is enough for this whole process, but that does not work that way if we want to do it thoroughly and completely without any special automotive tools at home.
Plus, I think it is extremely important to emphasize here that without any practical experience, we can easily cause serious damage to the engine if we do it incorrectly. So if we’re not 100% sure about this process and don’t have enough vehicle type related knowledge either, do not even start draining the cooling system, because the deaeration process is not always as simple as we think.
What types of fluids need to be prepared for this service?
Let's start with the coolant liquid itself.
I usually change the engine coolant using a suitable -72 °C concentrate and about 15 liters of distilled water. The color of the paints used for the coolant alone is far from enough information and can even be easily misleading. However, a little more scientifically, we can already say that there are G11, G12 and G13 type fluids on the market, which can have a very wide range of colors as this is a fairly manufacturer specific factor, thus it is absolutely clear that we should not choose on the basis of color, but on the basis of composition.
First of all, it’s worth knowing that these are essentially glycol-based - and not alcohol-based - liquids. Anyway, the type G11 is already considered quite obsolete, because steel block engines are being pushed out of the market. So this way the G11 is no longer really needed in the newer and more powerful vehicles, as it is based on ethylene glycol and is rich in various metal salts, phosphates and nitrites, which components reduce the cooling capacity, but at the same time they provide an excellent protective and sealing surface against corrosion.
The G12 coolant is also based on ethylene glycol, but typically does not contain the previously listed inorganic components, as they have been replaced by other organic additives to increase the heat dissipation capacity, which factor is more important for more powerful engines made from aluminum.
In contrast to the previous two types, the G13 coolant is already based on polypropylene, and this is only used for vehicles manufactured in recent years.
So let’s move on to the practical side.
The engine coolant can usually be drained using a small plastic tap - or screw - at the bottom of the cooling system. Furthermore, in my opinion it is NOT worth mixing the old coolant with the brand new one. Therefore, it is advisable to wash through the entire system profoundly at least three times with distilled water, since the replacement is done without deep disassembly, and a significant portion of the coolant always remains in the system.
So during the first washing process, the whole system is filled with a few liters of distilled water, and after the proper deaeration, the entire coolant content must be circulated in the engine.
I perform this deaeration process in several stages at the dedicated deaeration valves until the whole system becomes completely fluid tight, which is also indicated - during the engine idling - by the evenly splashing washing liquid, if the thermostat has already been opened.
In this reassuringly safe case, I close back the upper radiator cap, and allow the fluid to circulate in the passenger compartment during intense heating. After that the engine can be stopped and the cold washing liquid can be drained nicely.
Do not forget that the engine cooling system can be refilled with fresh fluid then and only then, when the engine has completely cooled down, otherwise unexpected cracks may occur in the engine. By repeating this washing process several times, we always get a much cleaner washing liquid, most of which is just distilled water, as shown by the fluid samples lined up in the image below.
Last but not least due to the fact that I always measure the amount of washing liquid after draining, so at the end of the whole process I know exactly how much distilled water is left in the system, thus, I can accurately calculate the freezing point of the desired fresh coolant too.
Thank You for reading this article!
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