Coolant Bleeding problem on KV6

[paulh260260]

Guys

Following on from my post about overheating I've now bled my coolant three times and yet again, after cooling overnight I still get a hiss when removing the header tank cap, or just loosening the bleed screw.

So If i explain exactly what I'm doing and the results of my actions maybe someone can tell me if I'm going wrong somewhere

1. Remove bleed tube from clip on top hose

2. Undo 8m bolt holding header talk to slam panel and bumper

3. Undo bleed screw from bottom hose, at this point there is no flow from the bleed screw hole

4, Unscrew header talk cap, At this point coolant starts gushing out of the bleed screw, no gurgle, no stop start just a constant flow.

5 Raise header talk and start filing with coolant. The coolant is flowing out of the bleed screw hole almost as quickly as I can fill the header tank.

6 At this point I have to lower the talk slightly as I need two hands to manoeuvre the bleed screw into its tight blind spot by which time the flow has stopped.

7. Refit the header tank and fill to the neck

8. Refit header bleed hose to clip on top hose

9. Make sure aircon and heating is off and rev engine at 2000 rpm

10. The coolant almost immediately goes to the top of the header tank spilling even more all over the place.

11 refit the header tank cap

12. Drive for a short time until fan kick in at 100 degrees.

I've even change over the header tank cap but still getting air out

As I said despite following this procedure three times there is still air coming out of the tank when cold suggesting I've not moved the airlock so what if anything am I doing wrong?

Cheers

Paul

[SD1too]

Hello Paul,

Here is the official MG Rover method for reference but it sounds as if you have already been following it.

When undoing the expansion tank cap on a cold engine a slight hiss, akin to opening a beer, is nothing to worry about.

If I were you Paul I would drain your cooling system fully, i.e. using the LH bank cylinder block drain plug as well as removing the radiator bottom hose and start from scratch. If you can, rig something to support your expansion tank leaving both hands free. Note from the official method that as soon as coolant starts flowing steadily from the bleeding orifice, the screw should be refitted. This shouldn't occur until you've poured quite a lot of coolant into the system. If it happens immediately, something's amiss.

By the way, the bleed screw is in the bottom radiator hose on its way to the thermostat.

Any comments?

Simon

[trikey]

Normally when you are getting a constant flow from the bleed screw that’s all you need?

[paulh260260]

Originally Posted by SD1too

Hello Paul,

Here is the official MG Rover method for reference but it sounds as if you have already been following it.

When undoing the expansion tank cap on a cold engine a slight hiss, akin to opening a beer, is nothing to worry about.

If I were you Paul I would drain your cooling system fully, i.e. using the LH bank cylinder block drain plug as well as removing the radiator bottom hose and start from scratch. If you can, rig something to support your expansion tank leaving both hands free. Note from the official method that as soon as coolant starts flowing steadily from the bleeding orifice, the screw should be refitted. This shouldn't occur until you've poured quite a lot of coolant into the system. If it happens immediately, something's amiss.

By the way, the bleed screw is in the bottom radiator hose on its way to the thermostat.

Any comments?

Simon

I see you've spotted my deliberate error Simon, I did of course mean the bottom hose for the bleed screw ( now corrected!)


It's the IMMEDIATE flowing of the coolant that concerns me,, that doesn't sound right but I suspect that a complete drain flush and refill looks sensible whilst I'm under her changing the oil as well

Paul

[paulh260260]

Originally Posted by trikey

Normally when you are getting a constant flow from the bleed screw that’s all you need?

You're right trikey but I don't think it'd meant to gush out immediately

Paul

[SD1too]

Originally Posted by paulh260260

It's the IMMEDIATE flowing of the coolant that concerns me ...

That might happen if the cooling system is still filled, as was the case with yours. Let us know what happens after it's been fully drained.

Simon

[Ducati750cc]

Might sound silly but is the hiss from pressure escaping, or a vacuum being released.

[bl52krz]

It should be the air being sucked into the system. With the header tank normally full to the top when the engine is at operating temperature, when it cools down, there is a ‘shrinkage’ of water, therefore there is a space in the header tank for a vacuum to form. When you undo the cap, this allows air to get into the tank..... the noise that you hear. If there is pressure, not a vacuum when you take the cap off, there is a different noise and you can feel it being ‘pushed’ away from the tank.

[T-Cut]

Apart from a 22psi-plus pressure relief valve, the header tank cap also has a hair spring valve to allow air in (if necessary) as the system cools down. Without a vacuum relief valve, the radiator would collapse following an overheat situation. So, there should be no hiss of air being sucked in when the cap is slackened. Similarly, there should be no significant hiss of air being released. If there is, you have to ask where does this excess pressure come from? The pressure when cold should be the same as it was the last time it was cold.



TC

[paulh260260]

Originally Posted by bl52krz

It should be the air being sucked into the system. With the header tank normally full to the top when the engine is at operating temperature, when it cools down, there is a ‘shrinkage’ of water, therefore there is a space in the header tank for a vacuum to form. When you undo the cap, this allows air to get into the tank..... the noise that you hear. If there is pressure, not a vacuum when you take the cap off, there is a different noise and you can feel it being ‘pushed’ away from the tank.

Ive checked again this morning and it definitely sounds like air being pushed out rather than being drawn in