Cooling System Flush

Last updated: April 19, 2000

Date: Mon, 30 Mar 1998 19:40:45 EST
From: KAWalanski

Trying to drain all of the coolant from a system: a) is unnecessary; and b) has risk unless you really know what you are doing.

Here is the procedure which has worked well for me over the years (n.b., this will have to me modified to account for the air-separator tank);

  1. Start with a stone cold engine

  2. Open the radiator cap

  3. Open the radiator drain plug and let out as much coolant as will drain';

  4. Replace drain plug and refill the sytem with distilled water

  5. Run the engine for for few minutes until it is warm (not hot);

  6. Repeat steps #3, #4 and #5 until you've effectively replace all of the coolant with distilled water. You'll know your finished draining the system when only clear water drains out.

  7. Drain the system one last time (now only residual distilled water should be in your cooling system);

  8. Suck out all the coolant in the overflow tank (I use a Turkey baster or a huge syringe with a short length of rubber tubing.)

  9. Replace the radiator drain plug.

  10. Add undiluted anti-freeze to the system;

  11. Run the engine to mix the distilled water already in the cooling system with the newly added antifreeze.

  12. Check the antifreeze/water concentration with a tester.

  13. Over the next few days, adjust to the desired antifreeze/water mixture over the next several days. You'll likely have to suck out a little coolant mixture from the fill cap to create room for either the distilled water or the anit-freeze you'll be adding to adjust to the desired concentration. Sometimes I adjust by adding either water or antifreeze to the coolant- overflow tank which utimately mixes with the engine coolant;

  14. Don't forget to add collant and/or water to the coolant overflow tank.

This may sound like a lot of work, but it isn't. The most difficult part is deciding the appropriate mixture to add to the coolant-overflow tank.

Date: Fri, 3 Apr 1998 20:22:00 -0600
From: "Westbrook, Chuck"

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 1/4 cup more. During this the overflow tank was filled 1/2 way of course.

From 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 fillips 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 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.

Date: Fri, 10 Apr 1998 01:30:30 -0500
From: tom

To purge cooing system:

  1. Fill the passenger side overflow tank to the full line on the dipstick.

  2. Fill the black expansion tank near the IC to the top.

  3. Fill the waterpump mounted filler to the top.

  4. Start the engine and turn on the heat till it blows warm. Shut off the car and let it cool.

  5. * Remove the waterpump 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 waterpump 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).

  6. Replace the cap and top off the waterpump filler cap. Restart the car w/ heat still on. Let it cool again. If the level drops at the water pump cap again repeat everthing after * until it the level there stays within 3/4 inch from the top.

  7. If you can't get it to stay topped off after 3 iterations, replace the coolant overflow system w/ this setup:

    Coolant Air Separation Tank Elimination from Rob Robinette.

This should be done anyway because that little black expansion tank will split from the heat. If you don't do the mod on the webpage, replace the expansion tank anyway with the one from Pettit (approx $135) to enhance reliability.

If you still loose coolant, have the cooling system pressure checked and the spark plugs checked for coolant- you may have a more serious problem.

Date: Mon, 18 May 1998 08:45:00 -0500
From: "Westbrook, Chuck"

When you drain your cooling system, you should also remove the drain plug on the left side of the block. It's located between the two rotor housings just above the oil pan on the left side. It takes a 14mm wrench. If you don't do this, the system will not drain completely.

Only use distilled water with your antifreeze + waterwetter solution.

The cooling system should be drained and refilled yearly. If you have been using tap water in the cooling system, then this causes mineral buildup, especially in the radiator. In turn this causes loss of cooling. If this is the case; then you will have to flush the whole system and then run some aluminum safe cooling system cleaner for a while to desolve the mineral buildup.

To help bleed air out of the system when refilling, remove the top cooling system hose from the throttle body.


Date: Sun, 16 Apr 2000 11:26:09 -0500
From: "Steve Wynveen" (

>I was following the how-to's on changing coolant today (the one on Steve
>Cirian's site) and I can't put in the reccomended amount.  I've only been
>able to put in in less than 1 1/4 gallons.  Rob Robinette's blurb in the
>how-to said that it takes 2 gallons. 

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.


Date: Thu, 8 Oct 1998 00:03:17 -0400
From: (Chris Sychlovy)

When filling, a way to get more coolant into the cooling system is to disconnect the ~5/8" O.D. coolant line which ties into the throttle body (this hose runs parallel to the firewall). This effectively burps the system and allows about 1 additional quart of coolant (about 6 total) to be poured in. Another tip is to pour very slowly... I think the fill rates are mentioned in the service manual.

(I think this is an elaboration on Chuck's tip above (Chris credited the idea to him, anyway. --Steve)

>anyone know a way to unclog a radiator?

Take it to a radiator shop. They call the process "boiling the radiator". I had it done to a massive 4-row unit in the old '69 Firebird I had. I can't remember if this is dipping it in acid or similar. I would guess it is some sort of chemical reaction like this, since I think it is lime that builds up inside.


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