How To Flush Your Car's Cooling System

Flushing the coolant in your vehicle's cooling system is a great step in maintaining a healthy engine. A failure in the cooling system can easily result in an engine damaged beyond repair and a wallet much, much lighter. Luckily, servicing a car's cooling system is easily within the grasp of the backyard mechanic. Spring and Autumn or good times to check your cooling system.

Take a moment to familiarize yourself with how your car's cooling system works. Below is a diagram illustrating a typical cooling system with the major parts of the system highlighted and explained.
The heart of any cooling system is the radiator. This large, flat tank of coolant is positioned at the front of your vehicle, just behind the grill. The radiator has many small channels that coolant flows through to dissipate heat. Directly behind the radiator will be one or two fans which help the radiator cool the antifreeze.*
On most vehicles, there will be a radiator cap on top of the radiator, on some, the cap is on the coolant recovery reservoir.
Cold coolant is pulled by the water pump, through the lower radiator hose, and into the engine. The coolant circulates throughout the engine, keeping it from overheating.
When the engine has reached normal operating temperatures, the thermostat opens, allowing the hot coolant to flow from the engine back to the radiator where it is cooled again.
When you turn the heat on inside your car, coolant flows from the engine into the heater core. The heater core is sort of like a miniature radiator located inside the dashboard that uses the heat from the coolant to warm the air in the car's cabin.

*The term coolant and antifreeze are interchangeable. This fluid has four main tasks: cool the engine, keep from freezing, keep from boiling, and keep the system from corroding.

What Type of Coolant/Antifreeze Should I Use?
Today's coolant market is confusing. In days past all coolant was the green ethylene glycol variety, but not anymore. Now it seems that every car manufacturer has at least one color of coolant. There are extended life coolants that now claim to go up to 150,000 miles before they need to be flushed and there are several "All Makes, All Models" type of coolant on store shelves. Which to use? Here is a pdf that has some good, technical information. If you want my simple answer, I would recommend using whatever coolant came with your vehicle. If you cannot find that or do not know, you can always use the tried and true green ethylene glycol. The only major drawback with the green stuff is its short 2 year coolant change interval, but even then, this short flush interval forces you to keep on top of your cooling system's maintenance, so I am not even sure that it is a drawback.

Common Problems With the Cooling System
Normally, your car's cooling system will work flawlessly for many years, but when a problem does occur, it is usually one of these:

• Leaking coolant (external) - a cracked radiator or old hose can cause coolant to leak. Replace any worn hoses or repair/replace the radiator.
• Leaking coolant (internal) - if your coolant level is dropping but you do not see any signs of external leakage, check the condition of your oil. If the oil is milky, then you have a blown head gasket.
• Leaking coolant (general) - if the coolant is not leaking out externally or internally, have your radiator cap pressure tested. A bad radiator cap may let steam escape, thus lowering the level of coolant.
  
• Coolant does not get cold - A broken fan clutch (if your fan is belt driven) or an electrical problem (if your fan is electrically driven) can disable the fan.
• Engine overheats - There can be many causes of this. First, check the coolant level in the radiator. Next, check for any liquid leaking out of the weep hole in the water pump; leakage here indicates a bad water pump. If the water pump and coolant levels are good, check the thermostat. A thermostat that is stuck closed will not allow coolant to circulate. When the engine is warm, feel the upper radiator hose. If it is hot, then the thermostat is not stuck closed.
• Engine takes a long time to get to operating temperature - The thermostat is stuck open, replace the thermostat.
• There is no heat coming out of the vents - A thermostat that is stuck open will increase the time it takes to get hot air out of the vents. If you do not get any hot air, the heater core may be plugged or bad.
• Coolant is leaking into the front passenger leg area - The heater core is clogged.

Flushing the Coolant on a 1996 Ford Ranger

Here is the method I used on my Ranger to service the cooling system.
There are several methods available.

There are four main steps in servicing the cooling system:

1. Flush the radiator
2. Flush the heater core
3. Flush the coolant recovery reservoir
4. Fill the system

Tools and Materials
You do not need much to flush your cooling system.

• The proper amount of coolant and water (check your owner's manual to find the cooling system's capacity)
• Pliers or screw driver to remove hose clamps
• Hose to direct draining coolant into proper container
• Large bucket or container to drain coolant into
• Garden hose attached to a water supply to flush the system
• Funnel to fill the radiator
• Chemical Cooling System Flush (optional) if your cooling system is very corroded or dirty, you may want to use a cleaner.
  

Flushing the Radiator

1. Start by removing the radiator cap.
2. Locate the radiator drain (on side of radiator, passenger side)
3. Attach a 3/8" inside diameter hose onto the drain nipple and route the hose into a large (4-5 gallon minimum) container.
4. Unscrew the draincock enough to let coolant drain from the radiator. You do not have to remove it. (If your car's radiator does not have a drain, you can disconnect the lower radiator hose to drain the radiator).
5. When coolant stops draining, use a garden hose at the radiator cap to flush the radiator. When the fluid coming out is clear, the radiator has been flushed. Let all the water drain, then tighten the draincock. Compare the color of your coolant to new coolant. If the old coolant looks good, then proceed to the next section. If the old coolant is rusty, or if chunks of rust and corrosion came out with the flush, you may consider using a chemical flushing agent to clean your radiator. Follow the manufacturer's instructions. On my truck, the old coolant looks really good, so I did not use any chemical cleaners.

Flushing the Heater Core

1. Locate the heater core inlet and outlet hoses. These two hoses will be located at the passenger side firewall. Follow the hoses to determine which is the inlet and which is the outlet. The inlet hose will come from the engine or thermostat; the outlet will come from the water pump.
2. Detach both hoses. Route the outlet hose so that it will empty into the drain container (I rigged up a drain pipe and hose).
3. With the garden hose, spray water into the inlet hose until the fluid draining from the outlet hose is clear. Alternate between a steady stream and short bursts to help dislodge any build-up inside the heater core.
4. Back flush the heater core by switching which hose drains and which you spray water into.
5. This step is optional, but you can repeat step #3 one more time.
6. Reattach the hoses, making sure they are properly routed (you do not want to get the inlet/outlet switched).

Flushing the Coolant Reservoir

1. Locate the end of the reservoir hose attached to the radiator pressure cap. Remove the hose from the cap and unclip it from the top of the radiator.
2. Route the hose so that the fluid drains into the drain container.
3. Open the coolant recovery reservoir cap. If the inside is fairly clean a simple garden hose flush is all that is needed. If there is a lot of scale and corrosion build-up, you may need to use a household cleaner to help get the tank clean. The reservoir on my truck had a bit of sediment in it, but not much.

Before proceeding to refilling the system with fresh coolant, make sure all hoses and drains are secure. Also, if your car is older, now may be a good time to do a little preventative maintenance and replace the thermostat.


Filling the System

1. Slowly add a 50/50 mix of antifreeze and water (distilled is preferrable) to the radiator. Use a large funnel. When done, leave the funnel in place.
2. When the radiator will take no more coolant, fill the reservoir to the "COLD FILL" line.
3. Set the heat controls all the way up.
4. Start the engine and let it run for 10 minutes AFTER it gets to operating temperature.
5. Shut the engine off and let it cool down. Add more coolant as necessary and reinstall the radiator cap.
   

There you go! I would keep an eye on the coolant level periodically for the next couple of days. If you think there may still be air in the system, you can purge it out by running the engine with the cap off the radiator.

Disposing of Used Coolant
"How do I properly dispose of used auto coolant?" This is a common question. The answer is to find out what your local laws are. Some recycling or hazardous materials centers will accept used coolant as will some auto parts stores. In some places, you can drain used coolant into the sewer as long as that sewer goes directly to a sanitation plant. In any case, always follow these guidelines:

• NEVER empty into a storm sewer or drain that does not end at a sanitation plant (septic systems are unacceptable!).
• NEVER pour into the ground.
• NEVER leave antifreeze uncovered - children or animals can be attracted to its sweet scent and taste and drink it, this is VERY dangerous and can be fatal!
• ALWAYS find out what the local laws are for properly disposing used coolant.
  

Other Coolant Flush Methods
I mentioned some other methods of flushing the coolant system. One simple way is to do a radiator drain and refill, then drive the car for the day, then repeat a few more times. However, using this method will not get the heater core or coolant reservoir properly flushed.

Another method is to purchase a flushing kit. These kits include a 'T' adapter that you install by cutting one of the hoses going to the heater core. Then you attach a garden hose and run the engine while the water purges all the old coolant out of the radiator. Finally, you add straight (not pre-diluted) coolant to the radiator until the proper mix is attained. This process does a good job of flushing, but you end up with tap water in your cooling system. I would personally not want all the hard minerals found in most tap water clogging up my radiator, so use distilled water when possible.