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How to Check Engine Coolant

Updated on April 30, 2018
Dan Ferrell profile image

Dan Ferrell writes about DIY car maintenance and repair. He has certifications in Automation and Control Technology and Technical Writing.

Overheating damaged the cylinder head on this engine.
Overheating damaged the cylinder head on this engine. | Source

Thousands of car drivers get stuck on the road every year because of cooling system problems. But a few simple checks can help prevent some common issues like:

  • engine overheating and failure
  • water pump failure
  • corrosion buildup
  • cavitation
  • diminished engine efficiency
  • engine damage

Car coolant--the mixture of ethylene or propylene glycol (antifreeze) and water--removes excess engine heat, lubricates the water pump, and fights corrosion and prevents cavitation. Besides, it helps a calibrated temperature gauge to work properly, and the engine to operate at a proper temperature, usually between 195F and 220F (91C and 104C), for better combustion, performance and low emissions.

Although a gauge or light on your dashboard can warn you of engine overheating, it doesn't tell you about coolant age, contamination or how efficiently the coolant is working. Thus, to spot potential problems, you need to regularly check coolant level and condition.

The next simple cooling system checks will help you:

  • prevent common car problems that can leave you stranded on the road
  • save you money in costly repairs

I. Checking Your Engine Coolant Level
II. I Can't Find the Coolant Reservoir Tank
III. Checking Coolant Condition
IV. Checking for Engine Cooling System Leaks
V. Coolant Maintenance Schedule
Checking coolant condition through the radiator neck.
Checking coolant condition through the radiator neck. | Source


Don't remove the cap from the radiator or coolant reservoir tank with the engine warm or hot. Boiling coolant may gush forth and cause severe burns.

I. Checking Your Engine Coolant Level

If not corrected on time, low coolant level can lead to engine overheating, head gasket failure, expansion of pistons and other components, and a cracked engine block.

To check coolant level, wait until the engine cools and reaches ambient temperature--a couple of hours if you've just driven the vehicle, or until the upper radiator hose is comfortable to the touch. Since coolant expands when hot, checking coolant level when the engine is cool not only prevents serious skin burns but inaccurate readings.

When you are ready:

  1. Park your car on a level surface.
  2. Pop the hood open and locate the coolant recovery tank.

    In most car models, you'll find the coolant recovery tank near the headlight, on the right front side of the engine compartment (passenger side). Look for a white plastic bottle with side level markings and a cap that may say "coolant only" or something similar. This bottle connects to the radiator through a thin rubber hose. Don't confuse this bottle with the windshield-washer reservoir, possibly located next to the coolant reservoir tank on some models. If necessary, consult your car owner's manual.

  3. Check the side markings on the reservoir. The coolant level should be at the LOW mark, or slightly above it. On some vehicle models, the level should reach between the LOW and FULL markings. Consult your car owner's manual, if necessary.
  4. If the level is low, add a 50/50 mixture of antifreeze and distilled water to the coolant reservoir tank. Make sure to use the antifreeze recommended by your car manufacturer. Consult your car owner's manual or vehicle repair manual. If you don't have this manual yet, you can buy an inexpensive, aftermarket manual at most auto parts stores or from a Web store.
  5. After adding coolant, check the level again during the week. If level drops again, check for a potential leak. Head over to section IV, "Checking for Engine Cooling System Leaks".

I Can't Find the Coolant Reservoir Tank

Some old vehicle models don't have an expansion tank or coolant reservoir (recovery) tank-- pressurized coolant recovery system--so you'll need to check the coolant level through the radiator neck.

  1. Park your car in a level surface.
  2. Wait for the engine to cool and then remove the radiator cap.
  3. After removing the radiator cap, look through the radiator neck. Coolant level should be about 1 inch (25 mm) below the bottom of the radiator filler neck.
  4. If you need to add coolant, mix 50 percent antifreeze and 50 percent distilled water. You can buy premixed coolant too. Although you can use universal type, check your car owner's manual for the recommended antifreeze.
  5. Check the coolant level the next day and add more until you get the correct level.

Coolant Protection

A concentration of 50/50 Antifreeze and distilled water provides:
Freeze protection down to -34F (-36C)
Boiling protection up to 265F (129C)
Rust protection
Cavitation protection
Proper operation of calibrated engine temperature sensor

Checking Coolant Condition

tCoolant level is the most common cooling system check done, but wearing of internal cooling system components, foreign particles that may find their way into the system, condensation and other factors may affect coolant concentration and change the freezing or overheating protection points. This is especially important on geographic areas where extreme high or low temperatures call for specific mix concentrations. So, its worth checking the condition of the coolant in your vehicle system from time to time.

To check coolant condition:

  1. Visually check the coolant through the reservoir or radiator filler neck.
  2. Inspect it for oil, rust, sludge and other foreign substances or particles mixed in the fluid.

    Coolant should be of a clear green, orange color or some other color if your manufacturer calls for a specific brand of coolant. But, if your coolant has a brownish, cloudy or rusty color, flush the system and refill it with fresh coolant. And always use the coolant recommended by your manufacturer for better protection. You can find this information in your car owner's manual or vehicle repair manual.

    If you find oil residues in the coolant--from the engine or transmission--you'll need to take in your vehicle for inspection and have the leak repaired.

  3. Check for coolant efficiency. There are several tools, like the coolant hydrometer, refractometer and test strips, that can help you check the efficiency of the coolant for your geographic area:

    The coolant hydrometer is an inexpensive tool you can buy at most auto parts stores. You can use it to know the freezing and boiling point of the coolant in the system. Just follow the manufacturer instructions that come with the tool. This way you know if you engine has enough protection for your geographic area.

    The refractometer. This tool is more precise and some also can be used to measure the specific gravity of a battery electrolyte and test brake fluid condition as well. So you have three tools in one.

    Coolant testing strips offer another practical way to find out the current efficiency of your radiator coolant. All you have to do is dip the strip in the radiator coolant, wait about 5 minutes and watch the chemical reaction that takes place on the special-treated strip. You then compare the strip color to a scale in the container to know the current freezing protection and coolant acidity (chemical break down).

Coolant can protect your system for two or five years, depending on the type of antifreeze you are using. Replace old coolant, even if it seems in good condition. No antifreeze product will control corrosion permanently. Once the coolant's protective properties deteriorate, corrosion sets in and slowly begins to destroy your radiator, water pump, and other system components.

A damaged head gasket can contaminate engine or transmission oil.
A damaged head gasket can contaminate engine or transmission oil. | Source

Checking for Engine Cooling System Leaks

A cooling system leak can begin small, without drawing much attention to it. And then escalate into a serious problem that can leave you stranded and with a costly repair in the middle of the road. Sometimes, a leak can give you a sign. For example, if you find yourself adding antifreeze to the cooling system regularly, you know the system has a leak somewhere. Either way, this simple checks may help you find a potential leak.

Look for wet, light gray color, or discolored areas around these cooling system components:

  • Water pump
  • Thermostat housing
  • Radiator (around the seams or tank walls)
  • engine freeze plugs
  • Coolant reservoir (cracks)
  • engine block
  • Heater hoses
  • Heater core

    Heater core leaks are hard to see because, in most car models, the core is hidden under the dashboard. So check the cabin's floor on the passenger side. If you find a wet spot there, most likely you have a core leak.

  • Radiator hoses

    Inspect the condition of the upper and lower radiator hoses. Check them for cracking, softening, hardening, splitting, bulging/swelling ends, or some other sign of deterioration. If they look too old or damaged, just replace them.

  • Between the block and cylinder head (gasket area)

    A blown cylinder head gasket, cracked engine block, or damaged oil transmission cooler tank can lead to coolant leaks and other serious problems. If you can't find the source of a potential leak, check the engine and transmission oil dipsticks. If the oil shows a milky white substance, a foamy appearance, or droplets of coolant, you've found the leak. You'll need to take your car to the shop to diagnose the problem.

  • Radiator cap

    A radiator cap falling apart, with dirty or ruptured seals, or with the wrong pressure rating for your particular cooling system can also cause coolant to leak. Check the seal for distortion and wear. And, if necessary, a car shop can pressure test the radiator cap for you.

If you can't find the leak, have the cooling system pressure tested. This is the most common method to find external cooling system leaks and head gasket leaks. If the leak is internal, a combustion leak test might be necessary.

Common Car Cooling System Problem Areas
* Radiator
* Radiator fan
* Hoses
* Thermostat
* Drive belt(s) or Serpentine belt
* Heater core
* Coolant level and condition
* Water pump
* Transmission oil cooler line

Coolant Maintenance Schedule

Check engine coolant level and condition on a regular basis. Regular checks give you the chance to spot potential problems as they begin to develop like frequent coolant low level, contamination and leaks. Key components in the system deteriorate over time, and fluids begin to find their way through weakened seals and worn out assemblies. So check the engine coolant at least once a week and every time you need to lift the hood.

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© 2015 Dan Ferrell


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