why does cooling an engine make it run better?


usually when reading about cars im told that this next generation model has vents that allow for better cooling of the engine which leads to better performance, im wondering why cooling some machinery allows it to preform better and if this is a universal thing or if some things run better when hot

In: Engineering

Some engines do run better hot- like diesels. But the real issue is that engines, like us, perform best at a specific operating temperature. Since the engine is producing waste heat any time it’s running, the challenge is keeping the engine at that temperature in order to maximize efficiency.

Better cooling apparatus allows an engine to efficiently and quickly reject waste heat without reducing its efficiency by requiring energy to circulate coolant or power cooling fans.

The engine can only work within a certain range of temperature, because of things like metal expanding and contracting with heat. If it gets too hot, the parts won’t fit together and everything breaks. Also, the faster the engine runs, the more heat it is generating, and therefore the more cooling it requires to keep it within the right temperature range. The engine being too *cold* is also a problem, but in most circumstances that isn’t a problem since it generates its own heat.

It doesn’t, really.

An engine works best if it’s at the temperature it’s designed for. For car engines that typically means a coolant temperature of 80-90°C, and there’s a thermostat in the cooling system that allows it to maintain this temperature. In other words, too hot isn’t good, but too cold isn’t good either.

High performance cars, especially turbocharged ones or ones that don’t have the engine in the front often have problems getting rid of the heat fast enough, so anything that provides more airflow is usually beneficial.

For economy cars that’s typically not an issue because the engines are less powerful and produce less heat as a result. These cars often try to get away with using as little cooling air as possible because in order to minimize aerodynamic drag and decrease the fuel consumption, having the air flow around the car is generally better.

Lets be super clear. A car engine is basically a container for thousands of explosions per second. The engine creates the conditions for those explosions, triggers them, then uses the energy that the explosions generate to propel the vehicle.

But heat, heat is a problem. Explosions generate heat and some heat is OK but to much will cause the metal in the engine to fuse together. This prevents the parts that we need to move from moving. Parts that are supposed to move but are actually melted together is very bad for an engine.

Heat also causes things to change size, this can cause parts to become jammed. This again causes parts that are supposed to move to not move and that’s bad.

The inherent problem with engines is that the explosions they are designed to contain also generate heat that can cause damage to the engine causing it to stop functioning.

So we need to add a whole bunch of parts and equipment that prevent this heat problem.

First we use oil. Oil is used anyplace that moving metal parts touch one another. This reduces the heat generated by the friction of those parts touching and moving. Without the oil the moving parts of the engine would eventually generate enough friction related heat to fuse them together without any explosion heat required. So when you include the heat from the explosions we need to be super careful about other heat sources like friction. So we use oil all over the inside of engine. Because we need the oil to always be all over the engine there are parts in an engine that distribute the oil, pump and oil and spray the oil.

For the most part the oil stays inside the engine (at least, it’s suposed to). For some cars the oil ends up getting too hot. So we need to pass it through a radiator known as an oil cooler. An oil cooler passes the oil through a series of pipes and blows air over those pipes. The oil goes in one end hot and comes out cooler. That’s mostly for higher performance cars, more normal cars don’t get the oil hot enough to require a seperate cooler.

Oil helps prevent heat from getting generated by friction but it dosent really do anything with the heat that the explosions are themselves generating. We need to do something with that heat because if we don’t we will run into issues.

So cars mostly use coolant. In the olden days this was just water but in modern cars we use a liquid designed for just this use and it does a better job that water alone.

Coolant is just a liquid and often it comes in a fun color (don’t drink it, it’s poison). Coolant gets circulated around the engine by a pump. The coolant gets pumped all over the inside of the engine through tiny pipes that are carved into the solid metal of the engine. It goes all around the engine and absorbs heat. It then takes that heat outside of the engine and passes through a radiator. Just like an oil cooler a radiator blows air over the pipes containing hot coolant and cools the coolant down. So it enters one end super hot and leaves the other end cooled down. It then cycles through the engine all over again getting hot and cooling down in the radiator, over and over and over.

So radiators and oil coolers (and intercooler on turbo cars) all take heat away from the engine, pass cool air over it and cool it down. But under the hood of a car is still a VERY hot place. The vents you ask about help with that part of the cooling process by allowing more fresh cool outside air to get into the engine area or by allowing hot nasty air to escape out of the engine area.

And to be clear. Cooler engines do not themselves perform better. It’s that higher performing engines generate more heat, and therefore require more cooling. The heat limitations of higher performing engines are basically the same as lower performing ones to preventing them from hitting that threshold is more difficult. Basically high performing engines generate more heat but can’t handle more heat, so they require more cooling. Better cooling allows for higher performance engines to exist without hitting that point where they break.

1. Simple diffusion: Particles move across their concentration gradient. If you want less heat in the engine, you should remove the heat surrounding the engine so the new air around it can absorb more heat from the engine.
2. Engines use internal combustion, if they get too hot, they’ll expand / seize up because it’s all metal inside rubbing together. You don’t want them to melt.
3. Oil lubricates these parts to keep them from experiencing high friction and to help cool them a little, the hotter your oil gets the sooner it will need changed.