I know that engine coolant is a fluid in the engine used to dissipate heat spots and keep the engine cool in general as the moving parts generate heat. In this context, I would call the oil an "engine coolant".

I also found out what happens when a cars engine doesn't have enough oil in it, which results in overheating among other things. But there is also a radiator in most cars to keep the engine coolant cool. However, due to the fact that oil is too viscous at cold and engine temperature to pass quickly through the thin pipes leading to the radiator to be cooled down by a massive fan. This is where another type of engine coolant comes in - a water based substance.

  • How does the cooling system work (i.e. how is heat passed from oil to water or air)?

  • Is there one pump for the entire cooling system (explain?) or two separate pumps (i.e. one loop for oil, one for water based substance) or more?

  • What exactly is supposedly referred to when someone says "engine coolant"? Oil? The water based substance? Air?

They are all fluids and they all serve the same purpose after all (I think).

2 Answers 2


Simple And Technical Definition Of Coolant

From a technician's standpoint "engine coolant" would be referring to the 50/50 mix of ethylene/polypropylene glycol and water. From an engineers standpoint engine coolant would TECHNICALLY be anything that assists the system in the cooling process. So, in this case you could refer to the fans, oil, and Anti-freeze (The 50/50 mix) as "coolant". By definition coolant is any liquid or gas that can be utilized to maintain a desired temperature for any situation needed. Technically "air" is a gas of sorts. Fans moving air in a manner that would cool down your engine bay, could be considered a coolant. Not to get to technical, but you asked =)

If your average Joe says coolant, they mean the Anti-freeze (50/50 Mix stated above).


In almost every car made from the early 60's, you have pumps for the propulsion of various fluids. The two main pumps are "water pumps" and "oil pumps". The water pump moves the coolant throughout the engine block, head, and air conditioning heating system. The oil pump moves oil throughout the engine block and head to provide lubrication, cleaning and sometimes pressure to certain internal components that may need it. These systems typically do "Loop". The most common return for oil passages are held within the head. The oil pools up just enough to reach holes that take it back to the bottom of the engine. Coolant typically runs on a circuit as well. How these are routed is very specific to the engine manufacturer. 99 percent of the time you have one oil pump and one water pump.

Heat Dispersion

I will say that your engine Anti-freeze does the majority of work. The reason is because the rate at which it circulates is far quicker than oil. It also has its own cooling assistance (The radiator). The entire system by nature is designed to handle the brunt of the job.

Oil does its part as well, but in a bit of a different way. Oil keeps the system cool by minimizing friction. The less friction, the less heat. As a fluid substance it has a good amount of potential to release heat, so it does that as well.

Air as explained above carries its purposes. Most manufactures use the grill or face of the car to route air into the radiator and engine bay. They also use air spoilers to route air into the engine bay. The ambient temperature at which an engine "lives" is actually very impacting on how well the engine can stay at its desired temperature. Not all engines do this though, it depends on the rate at which the engine turns and it's stresses. Hope this helps you understand a bit better, and I hope I answered your question well enough =)

  • Do not confuse the terms "coolant" with "cooling system" ... coolant is part of the cooling system, as well as the fans, radiator, water pump, etc. Coolant in automotive terms (why we're here) specifically refers to the wet stuff which transfers waste heat, aids in heat regulation within the engine, and brings heat inside the cabin. In your statement above, you are confusing coolant and cooling, which would not answer the question correctly. Commented Jan 13, 2016 at 12:27
  • @cloudnyn3 I don't know if you know this, so forgive me if you do, but in your first paragraph you said that technically air is a gas. This is true, but if you were trying to clarify to me that it is not a fluid then that is not the case. A fluid is defined as "anything that flows", which gases do just as much as any liquid. Commented Jan 13, 2016 at 16:34
  • Just making sure anyone who reads it understands that air could be considered a coolant. That's why I gave a simple definition and a scientific definition of the two.
    – cloudnyn3
    Commented Jan 13, 2016 at 17:04
  • Using this for the start of a tag-wiki for coolant. Commented Feb 4, 2016 at 8:06

The primary purpose of oil is lubrication, that is reducing the ammount of friction (and hence the ammount of heat produced in the first place). Some cars do have an "oil cooler" to transfer heat from oil to air but afait oil coolers are mostly seen on high performance cars.

Coolant is a liquid used to take heat away from the engine to the radiator which transfers it to the air. Usually the coolant is a mix of water and antifreeze (which is primerally ethelene glycol or propolene glycol). The coolant is circulated by a pump known as the "water pump".

Some engines do not use a liquid coolant and instead rely on direct cooling of the engine by moving air. These are refered to as aircooled engines.

In the short term it is possible to run an engine with plain water but doing so in the long term is not reccomended due to corrosion and freezing risks. There is at least one firm out there offering a waterless coolant option but opinions on whether it is a good idea seem mixed.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .