by Sam Dillinger (comments: 0)

Some ins and outs of your coolant system

filling the radiator

The coolant system of your vehicle is one of the most important, and least talked about, systems on your engine. There are quite a few things about it that people generally don’t know, but are really quite important. So let’s take a quick look at some of the features of the system, and some really important warnings about it.

Ok, we’ll start with what the coolant system does for your vehicle. It keeps the engine cool. The end… Just kidding, it’s not quite THAT easy. It does keep the engine from overheating, but most people don’t know how it does that. The chief purpose of the coolant in your vehicle is to wick heat away from the engine block and cylinder head, expel that heat, then repeat. That’s the most basic description. There’s more to it than that though. The coolant system is a closed system and is circulated through the engine system by the water pump, controlled by the thermostat, and also is what provides heat to the passenger compartment of the vehicle. In every cylinder of your engine there is a tightly controlled explosion that takes place on the combustion stroke. The combustion, or power, stroke is what is actually responsible for burning the gas you put in your car, and making your engine turn. I won’t say that it’s responsible for making your car move because that’s the job of the transmission, and it’s also a different discussion for a different day. After the explosion of the combustion stroke there is quite a bit of heat that would damage the metal components of the engine in short order if not removed. Enter the coolant system. It circulates through passageways drilled into the engine and cylinder head, which transfer the heat of operating to the liquid and it moves it away. The coolant flows to the radiator from there and the radiator fan, as well as the motion of the vehicle when you're driving, cool down the liquid, and the process is repeated.

Another basic aspect, but a really important one, of the coolant system is that when it reaches operating temperature it’s under constant pressure. Most coolant systems run at approximately 16 PSI. The reason behind this is because most liquids boil at 212 degrees fahrenheit, 100 degrees celsius. The temperature of the parts that your coolant is trying to cool down will exceed that very quickly and would boil the coolant, making it completely ineffective. Under pressure you can raised the boiling temperature and keep that from happening. This is why if you've ever had your engine overheat you hear a “bubbling” sound from the engine compartment. That’s the overheated coolant actually boiling. So maintaining the proper pressure is hugely important for the system to function correctly. The pressure is controlled by a spring on the radiator cap. Here comes the most important part of all: NEVER OPEN YOUR COOLANT SYSTEM WHEN IT’S HOT!!! When the coolant is under pressure and you release it without properly venting that pressure, it will literally shoot liquid at over 200 degrees straight up into the air. It’s hot enough to instantly blister your skin and much worse, especially if it were to touch your eyes. If you have to open your coolant system for any reason, open the hood and let the car cool for a minimum of 2 hours. That part is critically important to your safety.

As I mentioned, the coolant is also what’s responsible for heating up the passenger compartment of your car on those frigid mornings when the snow is piled up and the coffee still hasn’t quite kicked in yet. Pennsylvania, I’m looking at you (I’m from northern Pennsylvania and am sadly all too familiar with just how cold it is there at times). The coolant does this by taking the heat out of the metal parts of the engine and then a small part of the flow travels into what’s called a heater core which lives behind your dashboard. It’s basically a little radiator because it takes the heat out of the liquid moving through it and transfers it to the air blowing through it. That air is what comes out the vents of your car.

One final note on coolant: there are different types of coolant and they can NOT be mixed! Mixing them can create a very corrosive compound that damages the internal parts that the coolant runs through and can create very expensive repairs. Before ever adding any coolant to your vehicle be sure you read the owner’s manual, service manual, or contact your dealer and find out which coolant belongs there. If you're in a pinch and need some fluid to put in the system, use just plain water. It’s not good to leave just plain water in the system long term because it can rust the components and doesn’t transfer heat as well as the coolant/water mixture that is supposed to be in there, but it’s ok for a short distance/time period.

As always, for my members, feel free to drop me a line from with any questions!

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Meet Sam Dillinger

My name is Sam Dillinger. I've been a professional, dealership technician for 18 and a half years. My first introduction to mechanical repair was when my own vehicle broke down in the fall of 1995. I was 18 and couldn't afford to pay to have it fixed. So I borrowed tools and asked a ton of questions and, eventually, was able to replace the clutch on my truck by myself. During the course of that project, I found that I really enjoyed having a wrench in my hand and figuring out the puzzle of disassembly and reassembly of a motor vehicle.

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