S2 Coolant System Bleeding - how to

[Rusty]

SAFETY WARNING:-

The coolant system is pressurised when at operating temperature and so any leaks that go critical can cause an explosion of 90+degC coolant. If you're unlucky (and I was) you get this straight on your face and it HURTS A LOT! There's also the 3 hours in A&E to reflect on your previous good looks... I was lucky. If you think you have a leak, don't go poking about until the system pressure is released and the engine is off! This will make life a lot easier, trust me!

This is how I bleed the coolant system, had quite a bit of practice at this after my rad trouble a while ago:-

• Fill the system and get the level somewhere close.
• Remove the 3 screws on the header tank.
• Lift the header tank well above the rad - you can sit it on the mounting points
• Undo the rad screw so that it lets any air out - when the bubbles stop you're done.
• Re-fit the header tank & screws.
• Fit the header tank cap on securely.
• Make sure the fan is connected - I forgot to connect the fan on more than 1 occasion, no harm done though!
• Run the car up to temp, keeping an eye on the level - if it suddenly drops then stop the car, top up to the min level then re-start the process.
• Make sure the fan kicks in at 90+2 notches - higer suggests a leak / not pressurising properly.
• Turn it off and let it cool - overnight if possible.

With the engine off and cold:-

• Remove the 3 screws on the header tank.
• Lift the header tank well above the rad.
• Undo the rad screw to let any air out - again, when the bubbles stop you're done.
• Re-fit the header tank / screws.
• With the car on level ground fill it up to the min marker (this must be done cold!).
• Repeat the header tank trick if necessary.

You're now good to go but keep an eye on it for a run or two.

The leve shoulod be at min when the car is cold again and at max when at operating temperature.

Job Done

HTH

Update:-

If you have drained the heater matrix or pipework (e.g. when fitting a new block coolant pipe), then you will need to disconnect the engine to heater matrix pipe up by the strut brrace and back-fill the matrix / engine to prevent an air lock. On many cars, the plastic matrix bleed screw will have sheared, so you'll have to be a little creative to make sure that as little air is in the matrix as possible

[mcandmar]

Word of caution, dont go near the bleed nipple if the radiator is original. Plastic will be so brittle with age its guaranteed to crack if you even look at it. Good guide all the same

[Rusty]

It's a brass thread inset in the rad but worth exercising caution nonetheless.

Also, if you can get the rad screw out then worth replacing the fibre washer if it's screwed.

When tightening the rad screw, use the minimum of force!

[johne]

You can achieve the same effect as raising the expansion tank by just blowing into the tank gently - obviously on a cold car though.

You can get away with not undoing the radiator bleed screw as there is a vent pipe from the top of the radiator to the expansion tank and if you pressurise the system as I suggest then that will blow any air through the "U" in the vent pipe.

John

[Rusty]

The radiator bleed screw is higher than the small hose that goes to the header tank, thus it's difficult to bleed the radiator correctly.

[Jonas_R]

How can you bleed the coolant without opening the bleed nipple when the car is running?

[larsaskogstad]

I would like to add a comment on this.
Since some few problems I've talked with struggled the same as me with the bleeding.
I recommend to fill the system but also fill the hose that goes to the water rail and then re-fit it to the top of the rad.

After that I started to get circulation in the system after thermostat kicked in.
Use Mahle or Wahler thermostat. I changed my water pump uncessary but lession learned.

bleed1.png

[S2_avant 19930325]

You can achieve the same effect as raising the expansion tank by just blowing into the tank gently - obviously on a cold car though.

You can get away with not undoing the radiator bleed screw as there is a vent pipe from the top of the radiator to the expansion tank and if you pressurise the system as I suggest then that will blow any air through the "U" in the vent pipe.

John

When i blead mine , i hade the car running and get warm with the cap of ,, there should not be a issue to have the cap of from the start when its cold.Then i lifted the expension tank.