Flushing Your Cooling System
By Courtney Evans
Many cooling system woes can be completely eliminated with proper preventative maintenance. What kind of maintenance am I referring to? Well, your vehicle’s cooling system is made up of many components and parts. The list includes your radiator, water hoses, water pump, thermostat, heater core, and many others. These parts need to be periodically replaced based on their service life and the recommendations of your vehicle service manual. The subject of this article is not a cooling system part per se. We’re going to discus the liquid (coolant) that runs throughout the cooling system. This liquid is the agent that is responsible for actually moving heat away from your engine and is commonly called antifreeze.
Before we actually discuss flushing the coolant from your engine, let’s talk about the nature of the liquid cooled engine. I think you’re basic understanding of how the system works will greatly contribute to you properly performing a cooling system flush. I will discuss engine cooling in much greater detail in a subsequent article. I’ll just briefly touch on the subject here.
During the normal operation of your engine, vast amounts of heat are generated. The heat is literally generated by explosions within the cylinders of your engine. If this heat were left to go unchecked, your engine would overheat and cease to function because your oil and other engine components would fail and that’s just the beginning of your problems. Liquid is very good at dissipating heat, so this liquid is pumped throughout the nooks and crannies of your engine, thus removing the heat and taking it to an area where it can be cooled. This “area” is your radiator and it is located at the front of the vehicle.
The radiator has lots of surface area and fins that allow the heat to dissipate quickly. Once cooled, the liquid is then pumped back into the engine where the cycle repeats. This cooling process can actually be performed with plain water, however plain water has two characteristics that aren’t conducive to the practical operation inside an engine. First, water is not good at rust and corrosion prevention. In fact, it actually causes them. Second, water freezes at an unacceptable temperature for normal vehicle operation. Water good, ice bad.
So, we add antifreeze to the water to give it the desirable characteristics for operation within an engine. Most antifreeze is made from ethylene glycol and is typically dyed green, yellow, red, orange, pink, or blue. Because of the ethylene glycol, antifreeze prevents corrosion in the cooling system and freezes at a much lower temperature than water, almost making it the perfect substance for cooling an engine. I said “almost” because the problem with antifreeze, like most things, is that it cannot protect forever. Typically, it looses its protective properties after just two years or 30,000 miles. There are extended-life antifreezes available that protect for much longer, but those are the exception, not the rule.
Now that you know a little bit more about the nature of your cooling system and antifreeze, that brings us to flushing your cooling system. Let’s do it!
Caution! Make sure that your engine is cold. If you been driving your vehicle, let it cool for at least an hour before attempting to drain the system. The first thing you need to do is get rid of the old coolant. Remove the radiator cap so that you can let air into the system. You may have to raise the front of the vehicle to get to the bottom of the radiator. Another word of caution. This is a messy job, so make sure you have plenty of rags and paper towels handy. Also, wear goggles or safety glasses to protect your eyes. Coolant burns.
Some drain plugs require a special tool to open them. This tool is available at your local auto parts store. Some drain plugs can be opened by hand and others may require the use of pliers.
Make sure that you have a drain pan with a large enough capacity to catch all of the coolant. You can find the total engine coolant capacity in your owners or service manual. Move the dashboard ventilation lever to HOT to open the valve to the heater core. Now, open the plug and watch the show. If you don’t have a drain plug, just disconnect the lower radiator hose at the radiator. Removing the coolant from the radiator will evacuate about 45% of the coolant from the system. If your engine has a water drain plug on the engine block, removing it will help clear the antifreeze from the system faster than by just draining the radiator alone.
After the first draining, close the bottom of the radiator, fill the system with water, briefly run the engine, drain and repeat. Thus, “flushing” the system. You want to make sure that the final system draining reveals clear water and no more antifreeze.
If your city doesn’t have hazardous waste disposal for the spent antifreeze, the safest way to get rid of it is to pour it into a household drain, clothes washer pipe, or toilet. Don’t pour it onto the ground or into a storm drain. Make sure you keep the old and new antifreeze away from animals and children. It is typically sweet, tempting, and very poisonous.
The Filling and the Bleeding
Now that the system is clear of the old antifreeze, you need to fill the system with the new antifreeze. Again, check the total capacity of the system. You’ll fill the system with half antifreeze and half water. Some antifreeze is available pre-mixed 50/50 with water. If this is the kind you have, then you can just fill as-is.
This process takes a little care and patience to perform correctly. Because the engine block has lots of nooks and crannies, care must be taken to remove trapped air. The radiator fill cap and neck should be at the high point of the system to allow air to bleed out, however sometime this is not the case. So, if you have not raised the front of the vehicle, now is the time to do so.
Fill the radiator with the antifreeze or antifreeze/water mixture. You may have a bleed screw somewhere on the top of the engine. Follow the upper radiator hose. The bleed screw may be on the top of the radiator, on top of the thermostat housing located on the top of the engine, or both. If you have a bleed screw, open it to allow the air to escape. Slowly pour in the required amount of antifreeze until you see it oozing from the air bleeds and then close the bleed screws. Pour the remaining antifreeze into the radiator and top off the system with water.
If your system has a heater core valve, move the dashboard switch to COLD to close the system. Now with the engine running and warm, have someone move the dashboard switch back to HOT and listen to the valve. You should hear an initial rush of coolant into the heater core. After that, the valve should be silent. If you hear the gurgling sound of bubbles, air is still in the system. Check the whole system for leaks and then lower the vehicle. Make sure that you periodically check the coolant level in the system over the next few weeks. Continually top off the radiator as necessary as air rises to the top.
Here’s a quick breakdown of the steps:
1. Make sure the engine is cool and protect your eyes
2. Raise the front of the vehicle if necessary
3. Move the ventilation lever to HOT
4. Remove the radiator cap
5. Open the radiator plug
6. Open the engine water plug if you have one
7. Close system, fill with water
8. Run engine, drain and repeat
Filling and Bleeding
1. Raise vehicle if you already haven’t done so
2. Open bleed screws if applicable
3. Move the ventilation lever to COLD if vehicle equipped with heater coolant valve
4. Fill with antifreeze or antifreeze/water mixture
5. Close bleed screws when coolant oozes out
6. Have assistant move ventilation lever to HOT, listen for rush and bubbles
7. Check for leaks and lower vehicle
8. Check coolant level periodically over two weeks and top off as necessary
Removing old coolant and adding new coolant isn’t that difficult. It just takes a little time and patience. Performing this procedure at the proper intervals will aid in the protection of your cooling system components. You’ll have the satisfaction of a job well-done, a smile on your face, and an extra jingle in your pocket!