- [John] Hi, John here. In this video, we're
going to look at an engine cooling water system
and I'm going to explain to you how we regulate the
engine cooling water system temperature, in order to
prevent the engine overheating. So as you can see here,
we've got a 3D animation, what we're actually looking
at, is a four cylinder, in-line, internal-combustion engine. We've got four pistons, one, two, three, four, and they're in-line. We've got a crankshaft and
the crankshaft connects to an axial fan, this item here. Notice the fan is actually
driven by the crankshaft itself. We've also got a jacket water pump, there's this item. A thermostat, this item here and then we have a radiator. This is effectively, a heat exchanger. An expansion tank and all the associated hoses and piping. So what we'll do, we'll dive straight in and I'll walk you through what happens when an engine starts, and we'll look at the components as we go along. So let's play the animation, briefly. Okay, we can see our animation here. You see the engine is
cold, these blue arrows indicate the cooling water system is cold. If we get red arrows it
indicates that the cooling water system is becoming hot or is hot. We can see that the arrows are flowing around the combustion space
or around the cylinders, that's why we call it
a jacket water system. A jacket water cooling
system and a cooling water system are the same thing, so don't get thrown off by the wording. Jacket just means, literally, that the cylinders are wearing a jacket and that is to keep them on optimum temperature. What I'll do, I'll pause the animation, I'll zoom in and I can
show you what's happening. We have a cooling water
pump, it's this pump here, it's sucking from the
jackets of the engine and then we're going to send that cooling water to a thermostat. Now notice that the engine
is cold, so the thermostat is actually going to send the
cooling water down this way. I'll se if I can get
an arrow, there we go. It flows, coming along, and down here. We'll look at the thermostat
in more detail later, so don't worry too much about that now, but the cooling water is coming down and it is bypassing the heat exchanger, or the radiator. It's coming along here and it bypasses our radiator and it is recirculating. The reason it's recirculating
is, because we're not always trying to cool the engine, we wanna regulate the
temperature of the engine. That's the idea behind
the cooling water system. We wanna maintain, the
optimum operating temperature and this is going to be
around 80 degrees Celsius. So that's what's happening
when the engine is cold. So we've started the engine,
it's cold at the moment, but as it continues to
operate, it's going to generate more and more heat and
at some point we're going to see those red arrows coming
through, and there we go. We can see now the red
arrows are coming through, so the engine is hot,
but notice straightaway that the red arrows are being
diverted to the radiator. Let's zoom in on that. We can see now, that the
thermostat has changed position. The lower piece, or the
lower pipe, is now blocked, thermostat has blocked that piece off; however, the top part of
the thermostat is now open, you can see there's a gap in
the top and that is allowing the flow through the
top of the thermostat. The flow then, is going to the radiator and we're cooling that cooling water down, because this fan is
driven from the engine, it is blowing the air across the radiator, the air is symbolized by the white arrows, and we blow the air across the radiator, cool the cooling water
down, and we can see at the bottom here, we
got blue arrows again, so we've cooled, the cooling
water down, slightly. Other than that, the system is the same. So rather than using this pipe here, we're sending the flow, the other way and we're cooling the cooling water down. The thermostat though,
is a proportional device. It will open and close a relative amount, based upon the engine temperature. So if the engine is running very very hot, the thermostat will be fully open. So you can see there the
thermostat expanded, slightly, because the engine temperature increased and now the flow is going the other way. Let's back up again, see if
we can get that, in again. So there you go, a cold
engine slowly becoming hotter, now it is hot and the flow is gonna go, the opposite direction. This position though, of the thermostat as it is now, I'll see if I can
get it somewhere in between. Okay, as it is now, we've
got the same, effect, we've got the bypass closed
off, but it's important to realize that, thermostat regulates. It's gonna be opening
and closing, moving up and down, based upon the
temperature of the engine. So, sometimes it might not be fully opened or fully closed, or fully
bypassed, I should say. Sometimes it might be somewhere in between and that's because, the engine sometimes is not creating the
maximum amount of heat, maybe it's just idling and in that case, you might wanna send some cooling water to the radiator and
some through the bypass, that's why they call it a thermostat, because you're regulating
the thermal temperature. This is also a feedback
loop, because the temperature of the engine, is
controlled by the thermostat and then the cooling
water tells the thermostat what the engine
temperature is and then the thermostat regulates the temperature again by deciding the flow direction
of the cooling water. Let's have a look now at a
thermostat, in more detail. Okay, so here we are
looking at our thermostat, give it a little spin, so
you can have a look at it. You can see, on the top here, we've got a rod sticking out, this rod here. This whole section on the
top, the brass looking, or copper looking piece
is the primary valve around the primary valve
we have a black piece and she's a piece of, rubber-like material we used for sealing. The next black piece we have around here, is also used for sealing. You actually push this down into a recess within the engine and it sits
in there quite comfortably and then you'll put the
cover on, so it makes it quite easy to change the thermostat. You can also see there's an air bleed and if we go down, you can
see a spring, another spring. This section here is known
as the secondary valve or the bypass valve and
perhaps the most important item is the charge cylinder, which is this whole orange piece around here, so how does it work? We already know that if
the temperature increases then the top primary valve
will open and the bypass valve will close, so we're not
bypassing the radiator anymore and if the temperature
decreases, then the bypass opens and the primary valve
to the radiator, closes. So that's what it's doing,
but how it doing it? As you can see it's quite a simple design. Well, the way it's working,
is that there is wax within the charge
cylinder here and the wax is in a solid state, below
about 80 degrees Celsius. When the wax becomes
hot, it turns to liquid and when it turns to liquid, it requires more volumetric space,
or is of a larger volume and that larger volume will push a rod, out of the charge cylinder
and it will actually close our secondary valve
or our bypass valve. So this rod here, is from there to there, it actually goes up into
the charge cylinder. When the charge cylinder becomes hot, the wax melts, becomes
liquid, it's volume expands, it pushes the rod downwards and that then, closes our bypass valve. So this secondary valve
here is pushed down under the seat, and the
radiator or bypass is closed. So that's what's happening
when it's too hot, but at the same time, the
primary valve, this one here, will be opened and that means the cooling water is then going to our radiator. When the cooling water becomes cold again, the rod, here, will
retract, because the wax within the charge cylinder
has a smaller volume and requires less space, so
the rod retracts upwards, the bypass valve opens, and that means we are not sending cooling
water to the radiator. As you can see, we are
proportionately regulating the response of the
thermostat, in accordance with engine cooling water temperature. I'll click here, I should be
able to see the annotations. Okay and there we go, so
there's some annotations here, engine thermostat, what
it does, the air bleed, main valve, primary valve, et cetera, secondary valve also called bypass valve. So you can see all these parts labeled. This is available on the
website, so I encourage you to go there and
check out this 3D model. The cooling water system is
also available on the website, so go and check it out and
cement what you have learned. Let's go back to the cooling
water system model now, for the rest of the video. So hopefully now you understand how the cooling water system works. I just wanna do a quick
note here on thermal expansion and thermal contraction. Thermal expansion is catered
for by a header tank, that's this tank here. As the cooling water system gets hot, some of it may expand, if the temperature becomes very hot and the cooling water will go into this pipe and will store the cooling water in a header tank. So a cooling water header tank, allows for thermal expansion of the system. If we don't have this tank, then what's actually going to happen
is the cooling water will expand, it will pass
through a valve here, come out and just leap down the radiator or through the pipe and then leap down. So we have the header
tank there, so we can store the cooling water in the top and this allows for thermal expansion. The opposite of a very hot
engine, is a very cold engine and we also have to take
precautions against this as well. In order to protect the
engine from freezing, we will add antifreeze into
the cooling water system. The antifreeze prevents
the water from freezing, at for example, minus five degrees Celsius and it's very very important, that we do have the antifreeze in the engine. If we don't have the
antifreeze in the engine, what'll happen is, the
cooling water will freeze at minus five degrees, it will expand and we will rupture, or crack our engine, as well as potentially damage
of our engine components. So it's very important
that the cooling water is not allowed to freeze and expand. In addition to having
antifreeze in the engine, we're also gonna have
a corrosion inhibitor and this will help
prevent rust accumulating within the engine cooling
water system areas, such as the jacketed cylinder
liner, the pump thermostat, and all these corrosion inhibitors, stop rust accumulating
there, which ultimately may foul our heat exchanger and reduce the efficiency of the cooler water system. If you like this video, please do share it on social media or give
it a like, you can even leave a comment, that will be great, feedback is always appreciated. If you wanna learn more about engineering, then check out some of our
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