What some mechanic will tell you, Part I

My first car

I have owned my first car for three years now. A Nissan B15, year 2001. Needless to say, when I was buying this car back in the year 2009, everybody told me "Toyota" is the only car. Well it is now three years down and I have no regrets for buying a Nissan.


But what I will say basically applies to all cars. One advice I got from some mechanic was that immediately I get the car, I should have the thermostat removed. I was told that the thermostat is not meant for tropical countries like Kenya. Again I did not listen to the constant calls to remove the thermostat. I can assure you that up to this moment my car's cooling system is still intact.


However this is not to say that I have always had a smooth ride with this car for the three years I have had it. But certainly I have learnt valuable lessons.


Overheating

Let me talk about overheating which is something you will often see on Kenyan roads. It is almost a common phenomenon to see a car by the road side with its bonnet open and steam jetting jetting out from the radiator top. Even people who have not owned cars will tell you, "hiyo imechemuka". Simply meaning the car is overheating. Frankly speaking except for some brands like Range Rover or BMW I have basically seen every car brand with this symptom. But most notable are: Subaru Forester, Mitsubishi Pajero (old models).


Let me give you some background. Internal combustion engines used in all modern cars are very inefficient. This is because not all chemical energy from fuel is converted into kinetic energy to move the car. A lot of energy is converted into heat. Much of this heat does not help the car in moving. That is why all cars are equipped with gadgets that help dissipate this heat. Otherwise the engine will destroy itself. Most internal combustion engines have an efficiency between 18%-20%. Rocket engines have better efficiency, up to 70%. Because they operate at very high temperature and pressure. Needless to say, a car that runs hotter will most certainly be more efficient than one that runs cooler.


ECM/ECU

Modern engines are equipped with an Engine Control Module/Unit (ECM/ECU). This is actually an embedded computer in the car that ensures the optimum running of the engine. It receives input from a multitude of sensors interprets the data using multidimensional performance maps (look-up tables), and adjusts the engine actuators accordingly. One example is during a cold start. The ECU reads a low temperature from the coolant temperature sensor, The computer sends a signal that allows a rich flow of fuel-air mixture (more fuel, less air) to the combustion chamber. If you are keen enough you will notice that during cold start, your engine will almost be racing (high rev because of rich mixture). Immediately the engines heats up, the fuel-air mixture becomes lean (less fuel, more air). The engine audible revs reduce to a quiet hum.


What does the thermostat do?

This is a very important piece of gadget within the engine. And yes it works in all weather. Though its importance is much noticed in cold climates. It ensures that the engine is running at the right temperature it was intended to run at. This is the optimum temperature at which fuel consumption will be most efficient. If this device is missing or malfunctioning, the engine risks running too hot or too cold or not at all and hence will never achieve its intended fuel efficiency. 


I will just explain in layman's terms how the thermostat works. During a cold start the thermostat shuts coolant flow to the engine. This means the engine will warm up quickly hence allowing the ECU to quickly signal a lean fuel-air mixture to the combustion chamber. Once the engine has reached the rated operating temperature, the thermostat starts opening and allowing the coolant from the radiator to start flowing in hence preventing further rise in temperature. However with time, the coolant itself may become hot and therefore unable to cool the engine to its rated operating temperature. At this point the ECU reads a high temperature on the coolant temperature sensor and switches on the radiator fan(s). This cools the coolant in the radiator and hence the engine is able to run at a constant temperature.

Engine Coolant temperature sensor (ECT)


Points you should note about a thermostat and cooling system in general:

1. The thermostat helps the engine reach the operating temperature faster thus saving on fuel and internal wear.
2. If the radiator fans mechanisms has been interfered with so that they are always on and the thermostat has been removed, the engine will never reach optimum operating temperature (will always run cold). Fuel economy will be poor. This is because the ECU will always think the engine is in a cold start mode and hence more fuel, less air.
3. Have a faulty coolant temperature sensor replaced. Running with a faulty coolant temperature sensor causes the ECU to signal a default fuel-air ratio which in most cases is not economical. You might also have trouble during cold start.
4. A stack closed (never opens to let coolant into engine) thermostat will cause your engine to overheat as no coolant will flow into the engine. (This is the most sited reason for removing the thermostat. But this is more like staying in the house and starving to death for fear of being attacked by a lion if you go hunting!)
5. A stack open (never shuts coolant flow into engine) thermostat may cause problem during cold start especially in cold climates as cold coolant is always flowing into the engine. This is the same as a thermostat that has been removed. The engine will also take longer to reach operating temperature. This means faster wearing out of engine parts.

Watch out for part II of this article.