Cooling System Flush & Fill Procedure
by Chris Morris


First off, let me start by saying that the contents in this document are for use at your own risk.   Any damages to personal property or bodily damages are not the responsibility of the author.  If you agree with the above statement, then proceed with the rest of the document.  If you do not agree, please delete this document immediately. 


The following procedure is meant to be a guide to help you with the tedious task of servicing the cooling system on your car without removing the block plug and knock sensor.  I have done this several times on my cars and the cars of my Family and friends.  So far I have not had any complaints and I feel that I do a better job of it myself than to let a mechanic do it.  That’s not to say that I think all mechanics are inept and incompetent. 

Getting started-

Before you start to work on your car, get organized!  Make sure that you have all the tools, chemicals and safety equipment and have them close by so that this all goes smoothly and as quickly as possible.  You will need one gallon of ethylene glycol (green stuff) and about four or five gallons of distilled water.  Check your hoses and radiator cap and replace them if necessary.  You may also want to have a replacement thermostat handy and one 8oz bottle of Red line water wetter (optional). 

Safety equipment-

I cannot stress enough the importance of safety.  Do not at any time put yourself, your car or others in an unsafe situation.  Listen to that little voice inside your head.  I highly recommend the following personal protective equipment that will help you to do the job safely.


         Heat resistant rubber gloves

         Long sleeve shirt and pants

         Jack stands or ramps

         A large catch pan 

Comment: I do not recommend the use of Dexcool or leak sealing tablets.  Your best bet is to stick with the green ethylene glycol mixed 50/50 with distilled water.  The use of Red line water wetter will help your radiator to cool more efficiently and it also fights corrosion.  One bottle will work for the entire cooling system.  This is an ideal time to replace the thermostat and to delete the throttle body coolant.  I recommend a 160-degree thermostat from Hypertech. 

Get to work!

1.       With the engine cold, remove the radiator cap.  Make sure that your car is parked on level ground and you can reach the radiator drain plug. 

2.      Place a large container under the radiator drain to catch all of the coolant as it is drained. 

3.      Carefully unscrew the drain plug and let all of the coolant drain out into the catch pan.   If you can’t remove the drain plug, try removing the lower radiator hose.  If you need to do this, be very careful as the coolant will gush out and most likely drench you if you are not careful. 

4.      After the coolant has stopped draining, put the drain plug back in. 

5.      Remove the reservoir and dump the coolant into the catch pan and thoroughly clean the reservoir inside and out with fresh tap water.  You will need to remove the battery first as it sits on top of the reservoir.    

6.      Fill the radiator with distilled water to the top and turn the engine and heater on.  Do not put the radiator cap back on as you will need to top off the radiator with distilled water as the thermostat will open and the level will go down.   

7.      Let the water circulate for about five minutes and then turn the ignition off. 

8.      Once the water is cool enough, repeat step #3. 

9.      Repeat steps #4,6 until the water drains clear.  

10.  If you are satisfied that the water was as clear as it will get on the last draining, then you can go ahead with thermostat replacement and/or throttle body coolant bypass.  Be careful to not over tighten the thermostat housing bolts, as they just need to be snug.  If you want to delete the throttle body coolant, then follow the directions in step 10a. 

10a. Disconnect the black coolant lines on either side of the throttle body.  Be ready to catch the coolant that will drain out of the throttle body and lines.  Route the lines so that they meet and overlap each other.  You will need to cut about 2 to 3 inches off one of the ends so that they come together flush.  You will need a 3/8” brass fitting and band clamps to join the two lines.  Once this is done secure the lines with some zip ties so that they are out of the way of the fans.  On my Camaro, I routed them on top of the fan shroud and under the intake elbow.  Plug the metal fittings on either side of the throttle body with vacuum line caps and you’re done. 

11.  Install the reservoir and fill it about half way with coolant and distilled water mixed 50/50.   Use the dip stick to measure the level as it should be at the cool line. 

12.  Put in one gallon of coolant into the radiator as there will be approximately one gallon of distilled water in the block.  Fill it to the top and then turn the ignition on and let it circulate for a few minutes.  This will allow the large air pockets to purge and you can top off the radiator when the level goes down. 

13.  Turn off the ignition and put the radiator cap back on.  Check for leaks or any other loose items as you are about to bleed the cooling system.  Make damn sure that you used a reverse flow thermostat and that you installed it properly.  If it is not done right, your car will soon over heat.   

14.  You’re almost finished!  Drive your car up on ramps or use jack stands to get the nose up in the air.  You need to do this in order for the tiny air bubbles remaining in the system to escape through the bleed screws.  Don’t forget to pull the emergency brake handle up. 

15.  With the engine running, the car in park and the parking brake on, open the top-most bleed screw until a steady stream of coolant comes out.  Be careful not to get any coolant on your optispark.  What I do is form a funnel, or deflector out of aluminum foil.  You can form it around the bleed screw on the heater hose and route it down to the catch pan. 

16.  Once there are no more air bubbles coming out of the bleed screw close it, but be careful not to strip the threads as it is made of soft brass.  Make sure everything is closed and tightened and then put your car back down on the ground and go for a test drive. 

17.  While driving check for the low coolant light and observe the temperature gauge.  If it starts climbing into the red zone you better find a place to pull over and find out what’s wrong.  If you notice that the needle on the temp gauge bounces a little, there is probably still air in the system and you will need to go through the bleeding process again.   Don’t worry as this is normal, it just takes a little time and driving to get all of the air out.  Be persistent, as air bubbles will form hot spots on the heads and cause detonation. 


Well, I hope that this document has helped you to successfully service you cooling system.   If you have any questions or constructive criticism, please e-mail me at  Best of luck to you and feel free to give this to anyone you feel can use it. 

Best regards, 

Chris Morris

A.K.A. Chris 94Z A4 on the forums

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