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How to Flush the Radiator

By Rob Robinette

You will need 1 gallon of antifreeze and 2 gallons of distilled (not mineral) water. You can get the water from the grocery store for about $3. You will also need a Phillips head screwdriver, a 2 gallon bucket, a cloth rag and a funnel.
The coolant system capacity is 9.3 US quarts (2 gallons, 1.3 quarts) and you won't be able to drain that last 1.3 quarts of coolant so 1 gallon of antifreeze and 1 gallon of water will give you about a 55% antifreeze to water ratio. This percentage will give you max protection from freezing, down to -40 degrees F. If you don't need that much freeze protection 35% antifreeze will protect you down to 3 degrees F and will actually cool the car more efficiently.
Warning: Don't try to drain the coolant system unless the car is really cool or you may get burned. Start by relieving the pressure by opening the coolant cap on the engine (not on the plastic overfill tank). Then put the cap back on to minimize the amount of fluid that will drain onto your hand when you remove the plug. The drain plug is in the bottom of the radiator and is accessible from beneath the car (you may have to raise the front end). There is a 1 inch round hole in the plastic engine bay floor pan about 1 foot from the spoiler and near the center line of the car (it's the only round hole I saw). Completely remove the drain plug, put the bucket in place and then remove both coolant caps to help the system drain. Warning: Antifreeze smells and tastes great to animals and it will kill them, don't leave this stuff lying around. Take it to a recycling station.
Flush out the system by pouring in about a half of a gallon of distilled water. Wait for it to drain and reinstall the plug. If you want to really flush out the system then fill it with distilled water, replace the radiator cap and run the engine for about 3 minutes with the heater on full hot and then drain it again. If you do the double flush you will need another 2 gallons of water.  Add the water and antifreeze to get between 35% - 55% antifreeze. I recommend alternating between the two fluids because you can't be sure how much fluid will actually be needed to fill the system. You can minimize the air bubbles in the system by gently squeezing and pulsing the large diameter coolant hose that runs by the right side of the intercooler. Check the fluid level in your overflow tank (white tank near the front right wheel). The only way to replace it's fuel is to suck the fluid out or remove the fender wheel liner and take out the tank. I just added some water and coolant to get the level close to the F line on the dipstick.
IMPORTANT: You must "burp" the coolant system. Run the car for a about three minutes (don't drive it yet because you may be low on coolant) and shut it down. Put a rag over the engine coolant cap and open it up, pulse the big coolant hose, and top it off. You will need to do this several times. The first time you drive it take some water with you because you may get the "Add Coolant" buzzer and you don't want to drive the car for more than about 30 seconds with the buzzer on. Remove the radiator cap and top off the coolant level before you drive the car for the next three drives and you will have a well purged coolant system.
Rob Robinette

People keep asking me how to purge their cooling system. To purge cooing system: fill the passenger side overflow tank to the full line on the dipstick. Fill the black expansion tank near the IC to the top. fill the water pump mounted filler to the top. Start the engine and turn on the heat till it blows warm. Shut off the car and let it cool. *Remove the water pump filler cap. if the level dropped more than 1 inch, remove the cap on the black expansion tank and fill it to the top. (if less than 1 inch, fill water pump filler cap to the top, restart the car w/ heat still on, now you should be OK, just recheck every day or 2 until the level stabilizes). Replace the cap and top off the water pump filler cap. Restart the car w/ heat still on. Let it cool again. If the level drops at the water pump cap again repeat everything after * until it the level there stays within 3/4 inch from the top. If you can't get it to stay topped off after 3 iterations:
Replace air separation tank (black plastic) w/ this setup: coolant_tank.htm
This should be done anyway because that little black expansion tank will split from the heat. This has caused slippery coolant to spray out under the tires and loss of control of vehicles in more than one instance. If you don't do the mod on the web page, replace the expansion tank anyway with the one from Pettit (approx. $135) to enhance reliability. If you still loose coolant, CAREFULLY check the hose from the black expansion tank to the coolant recovery tank near the air filter. Even a tiny pinhole or bad seal on this hose will prevent coolant from being siphoned back into the engine on shutdown, which will eventually lower the level of coolant in the engine. If everything still checks out, have the cooling system pressure checked and the spark plugs and oil checked for coolant- you may have a more serious problem.
Tom Jelly

When my car was at MazMax here in Houston last fall (turbos were being pulled), the mechanic gave me this tip which is fantastic. Remove the top coolant hose from the throttle body (is in the rear near the firewall) when refilling the system. Today I did a cooling and heater system hose replacement job, along with eliminating the coolant separation tank (installed the 86-88 pressure cap neck). I removed the top hose when I started filling the system. This was the first time in 6 years that the system almost took the full amount, about 8 quarts. After filling, replacing the hose, and running the engine for 2 minutes, it only took about 1 pint more. Then I drove the car until fully warmed up and let it cool down; it then took about cup more. During this the overflow tank was filled way of course.
Chuck 93 R1

WARNING
The most important tip is to make sure the drain plug still has a rubber gasket/washer on it before putting it back in. I did not know this plug was there, and had I not seen it in the pan I had drained the coolant into, I would have never known any better. The washer must have stuck to the radiator and then fell off as the coolant was draining. Nearly a disaster.
Jose

Did you take out the block drain plug, located on the mid-housing, just above the oil pan rail? If not, you left a lot of fluid sitting in the engine block. The plug is just a scaled down version of the oil drain plug - straight threads, with a crush washer. I can't find it mentioned anywhere in my '94 shop manual, so I just tighten it down by feel. On my car, there is a blind tapped hole next to it, with nothing in that hole.

The coolant drain plug on the engine block

 

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