- Car Care & Maintenance
How to Change Coolant without Causing Engine Overheat
You can change coolant in your own garage without leaving behind air pockets — a common problem in many modern vehicles that lead to engine overheat.
As the protective qualities of antifreeze degrade over time, acid content increases and rust spreads out. Soon after, corrosion begins to destroy your water pump, radiator, and surfaces throughout the engine.
That's why car manufacturers suggest a two- or five-year service interval or more, depending on your particular vehicle make and model and the type of antifreeze you're using.
So the sooner you change that old coolant in your car, the better. You'll only need a few common tools.
Work on this car maintenance project on a Saturday morning with the help of this guide and without fear that your engine will overheat afterwards.
Just follow these steps.
Draining the Cooling System
Before you start, find a well ventilated area with a level surface — if you need to raise your car — and with enough room around your car to comfortably change the coolant.
1. Wait for the engine to cool before removing the radiator cap — or the reservoir cap if there's no radiator cap. This will prevent hot coolant from gushing out and burning your skin.
2. Find the petcock towards the bottom of the radiator. On some vehicles, you need to raise the front of the car to gain access to the petcock from underneath. If this is so, use a floor jack to raise the front of your car and secure it with a jack stand. Also, block the rear wheels with a couple of wooden blocks and set the parking brake.
3. Place a drain pan under the car toward the radiator drain valve.
4. Loosen the petcock with your hand or a pair of pliers or a wrench.
Some radiator drain valves have little room around them you can hardly reach them with your hand or tool; others tend to rust over time you don't want to remove them for fear of causing some damage. Instead, try removing the lower radiator hose to prevent an expensive repair.
* To do this, loosen the clamp holding the hose at either end, whichever is more accessible to you — depending on the type of clamp, you'll need a screwdriver or a pair of pliers for this.
* Then break the hose grip at the fitting using a pair of slip-joint pliers by carefully twisting the hose just a few degrees.
* Once you brake the grip, manually twist the hose back and forth as you pull it off its fitting. Let the old coolant drain into the drain pan.
5. Loosen the radiator cap and wait for the coolant to drain completely.
6. Locate the block drain plug or plugs. They're located on the side of the engine. Consult your car owner's manual or your vehicle service manual. If you don't have the manual, you can buy an aftermarket copy at your local auto parts store or online.
On some engines, it's almost impossible to remove the drain plugs without some special tools or equipment because of their location or because they seemed to have sealed to the block. Still, other engines lack a drain plug. For these cases, follow the next alternative method.
* After adding fresh coolant to the radiator and reservoir, following the next steps, run your car for a week. Then, drain the radiator and reservoir again and add more fresh coolant to the system. Follow the procedure to remove air from the system as well. Changing the radiator and reservoir coolant twice will replace most of the coolant in the system.
7. After removing the plugs, wait for the coolant to drain completely.
8. After draining the coolant completely, flush the radiator using a garden hose to remove sediments. Run water through the radiator until water flows clear through the radiator drain valve. If you think you need to remove rust and scale from the radiator, get a radiator cleaner from the auto parts store and follow the instructions from the manufacturer.
9. After flushing the radiator, tighten the petcock or reinstall the lower radiator hose, and engine block drain plugs.
10. Now, remove the coolant reservoir, empty the coolant into the drain pan and flush the reservoir.
11. Reinstall the reservoir.
Cooling System Bleed Methods
Depends on car model
Works on most models
Works on most models
Many pre-1995 models don't need bleeding
Refilling the Cooling System
With the coolant removed and the radiator and reservoir cleaned, it's time to refill the cooling system. Before you start, check and see if your system has a purge valve (aka bleeder screw). This is a small, single screw, usually located on the thermostat housing, which connects to the upper radiator hose on the engine side. Check your car owner's manual or vehicle repair manual.
The purge valve will expel any air that gets into the system after adding the new coolant. This will prevent the formation of air bubbles or hot pockets inside the engine that cause overheating.
Using Alternative Methods to Bleed Air from the Cooling System
* Another way to purge air from the system is to use what I call the jack stand method. All you have to do is raise the front of your car to position the radiator neck (fill point) at a higher level than the heater core — this is the small, radiator-like component (usually located underneath the dashboard on the passenger side) that provides warm air to the vehicle interior.
This will prevent the coolant from trapping air bubbles. If you do this, secure the front of the vehicle with a couple of jack stands, block the rear wheels with wooden blocks, and engage the parking brake.
* Also, a highly recommended method is the use of a special funnel that makes it easier to fill up the radiator or cooling system without introducing air into the system. Check the Amazon ad below and the video so that you have an idea how it works. Follow the instructions that come with the funnel, if you decide to get one.
Use the most convenient method for you, but make sure to purge the air from the system. Otherwise, air bubbles will prevent proper coolant flow, and overheat and damage your engine.
* 45 degree elbow allows use on radiator caps that are placed at an angle
* The E-adapter is used on the surge tanks on many Ford applications
* The spill-free funnel eliminates trapped air pockets which usually cause erratic cooling system and heater performance
* Extension allows access to caps located under shrouds or in fender wells
1. Set the heater temperature control to the maximum.
2. Slowly add a 50/50 mixture of distilled water and antifreeze — the one recommended by your car manufacturer — to the radiator until it reaches the bottom of the radiator neck.
NOTE: If you live in an area with extreme climate conditions, you'll need to increase the amount of antifreeze to the mix. Also, some car manufacturers recommend using a premixed coolant to add to the system, while others recommend a specific type of antifreeze that you need to mix with distilled water before adding it to the cooling system. Check your car owner's manual or vehicle repair manual for the right premixed-coolant or antifreeze you need for your specific car model.
3. Also, fill the reservoir with fresh coolant up to the Low mark.
4. Leave the radiator cap off and start the engine.
5. Let the engine idle — between 15 and 20 minutes — until it reaches operating temperature. At this point, the thermostat will open and you'll see through the radiator neck how the coolant begins to flow and the upper radiator hose starts to get hot. The coolant level will drop.
6. Add more fresh coolant to bring the level up to the bottom of the radiator neck. Wait a few seconds for the coolant to circulate and the trapped air to come out.
* If you're purging the air through the bleed screw, crack the screw open using a wrench and let coolant flow through the valve until you see coolant flowing free of air bubbles. Then tighten the screw. On some models, the bleeding procedure will differ from the one described here. Check your car owner's manual or vehicle repair manual for specific instructions for your car make and model.
7. Turn off the engine and let it cool.
8. Top off the coolant in the radiator to the correct level — usually about an inch below the bottom of the radiator neck. Then, squeeze the upper radiator hose to expel the air and add more coolant if necessary.
9. Add more coolant to the reservoir up to the Low mark, if necessary.
10. Replace the radiator cap.
11. Start the engine again and let it reach operating temperature and check for leaks.
When you need to change coolant in your car, don't forget the most critical part, bleeding the cooling system, specially on car models with low-profile radiators. Trapped air will seriously disrupt the system and cause costly damage. By replacing the coolant at the recommended service interval, you are removing dirt and rust particles that eventually corrode, block radiator and heater small passages, and cause serious system damage. So follow this guide every time you need to service the cooling system.
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