Coolant bleeding?

[Rich Lewis]

Just changed my spark plugs and I disconnected the water feed, not sure if I needed to do the job or not, either way I did, what's the best way to bleed the coolant system?

[Steve]

When the car is cold. Remove the rad cap. Fill up to the top. Start car and put the heater on its hottest setting with the fan on full. I then found the easiest way to force the air out is to squeeze the two pipes at the rear off the engine that go to the heater matrix (careful though they will get hot). You should see air come out of the rad. Just keep topping with fluid as needed. After about ten minutes of this you should find the heater gets hot. Replace the rad cap, top up the expansion tank to the required level and enjoy.

[Ian C]

Just to add to this, once you've done that bleed you then get the rest of the air out like this:

 

1. Fill the expansion tank to full
   
2. Run the car up to temp
   
3. Let it cool
   
4. Repeat until you don't need to fill the expansion tank up again
   

 

Reason for this is that the air gets forced out of the expansion tank when the system heats up, but coolant is drawn back in from the expansion tank as it cools down. This self-bleeds the system as long as you keep the expansion tank filled up. Takes about 3 cycles.

 

-Ian

[Scoboblio]

While we're on the subject, do you end up with air in the system if you use the drain plug on the bottom of the rad to change the coolant, rather than removing the bottom rad hose? The reason I ask is that I changed my coolant yesterday using the tap, having followed the above advice I *saw* no air bubbles at all coming out from the radiator with the cap off.