‘How much coolant should I put in my car?’ [Newbie Guide]

Updated Jun 15, 2021 | Same topic: Beginner's Guide

The coolant reservoir tank should neither be empty or full. 

Even if a car makes you look and feel cool, they actually run hot under the hood. The standard automobile converts fuel to motive power by means of internal combustion, which is why engines are made from either aluminum alloy (for gasoline) or iron (for diesel).

Engine bay

The engine needs to burn fuel in order to release its energy

But the very material that makes engines withstand the heat of these mini explosions also contributes to it, with many moving parts resulting in significant amounts of friction. While lubricants and sophisticated coatings along the cylinder walls handle part of the problem, the engine relies mainly on its cooling system to keep temperatures stable.

An important part of this system is the radiator coolant, the fluid that’s pumped throughout a running engine to carry heat away, then cooled down to make the same journey all over again. Having sufficient amounts of the stuff in the coolant reservoir (or overflow) tank spells the difference between getting to your destination safely and your car suddenly stalling while spewing steam from the hood.        

Reservoir tank

Pay attention to the markings along the reservoir tank's body

Checking the engine’s coolant level, especially before a long drive, is a vital part of your car’s maintenance routine. If you look closely at the body of the reservoir tank, there are two markings: F (Full) and L (Low). The coolant level should ideally be between these two.

An engine’s cooling system is usually a closed loop, with minimal loss of coolant. However, some of the fluid does boil away as vapor, which means that you will occasionally need to add more coolant, especially if the car is frequently used. Once you see the fluid level getting closer to the bottom mark, top up the reservoir with the coolant type your car uses.    

Pouring coolant into tank

Pour coolant into the reservoir tank, not directly into the radiator    

What you should avoid is overfilling the reservoir tank. You’ll notice that the F mark isn’t situated at the tank’s brim. The reservoir tank is not meant to be filled all the way through, as the cooling system is pressurized and the extra space at the top is needed for the fluid to expand.

Overfilling the tank takes away that allowance, resulting in a steady buildup of pressure that can cause the tank to burst. The coolant could find its way into the car’s electrical system and damage it, or it will be spilled on the ground and reach waterways, posing an environmental hazard.      

Find more tips for beginner car owners at Philkotse.com.

Joseph Paolo Estabillo

Joseph Paolo Estabillo


Joseph has been a member of various car clubs since he got his driver's license in 2004 – old enough to remember riding in taxicabs with analog meters, but his fascination with cars goes way back. After nearly two decades of working in broadcast media, he shifted gears by coming on board as Philkotse’s first Filipino member and staff writer in 2017.

Apart from his role in Philkotse as Content Team Lead, Joseph has written episodes for Drive, which has been airing on CNN Philippines for five seasons running. He has also delivered content for various car dealerships based in the U.S., spanning multiple brands such as Alfa Romeo, Maserati, Jeep, Dodge, among others.

Keeping his hopes high and his revs low, he dreams about owning a Kei car when he retires. Hates slow parkers.

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