Coolant Bleeding problem on KV6

[T-Cut]

Originally Posted by paulh260260

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

Originally Posted by T-Cut

- - - - 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.

Maybe try the fast test. With engine stone cold, open the pressure cap to ensure it starts off at atmospheric pressure. Screw cap back, start the engine and rev it to around 3000rpm for 30-60 seconds. Stop the engine, which will be nowhere near warmed up. Unscrew the cap and observe/listen for gas release. Obviously there shouldn't be any significant hiss.


TC

[paulh260260]

Originally Posted by T-Cut

Maybe try the fast test. With engine stone cold, open the pressure cap to ensure it starts off at atmospheric pressure. Screw cap back, start the engine and rev it to around 3000rpm for 30-60 seconds. Stop the engine, which will be nowhere near warmed up. Unscrew the cap and observe/listen for gas release. Obviously there shouldn't be any significant hiss.


TC

Thank TC Ill give that a go tomorrow morning and report back

Paul

[paulh260260]

Originally Posted by T-Cut

Maybe try the fast test. With engine stone cold, open the pressure cap to ensure it starts off at atmospheric pressure. Screw cap back, start the engine and rev it to around 3000rpm for 30-60 seconds. Stop the engine, which will be nowhere near warmed up. Unscrew the cap and observe/listen for gas release. Obviously there shouldn't be any significant hiss.


TC

Tried the fast test as suggested and on releasing the header tank cap there is a slight hiss of gas following the fast test.

Paul

[T-Cut]

Originally Posted by T-Cut

Obviously there shouldn't be any significant hiss.

Originally Posted by paulh260260

- - - there is a slight hiss of gas following the fast test.

Significant or slight, that is the question.

This test is one of several simple diagnostic ways for assessing exhaust gas getting into the cooling system. Residual pressure in a stone cold coolng system can only be the result of a permanent gas being pumped into it. This quick test on its own isn't a reason to run around shouting HGF, but it's an abnormal sign. Obviously, the cooling system pressure rises anyway as it warms up, so just few degrees warmer than 'cold' will pump it up a little. If there's any air bubbles anywhere near the heads, then the pressure will rise much quicker as the air warms and expands. So, the system must be properly bled for the test to work correctly. It can only be considered proof positive if there's a significant pressure generated after a few seconds running. There's that 'significant' again. I suppose whether it is or not significant is basically down to personal judgement. You might repeat the test for a little longer while the head temperature's displayed on the diagnostic screen. That way the start and end temperatures are another bit of info. Clearly, if a small gasket leak allows exhaust gas into the coolant when you're driving, there's always going to be 'air' that needs bleeding out.



TC

[paulh260260]

Originally Posted by T-Cut

Significant or slight, that is the question.

This test is one of several simple diagnostic ways for assessing exhaust gas getting into the cooling system. Residual pressure in a stone cold coolng system can only be the result of a permanent gas being pumped into it. This quick test on its own isn't a reason to run around shouting HGF, but it's an abnormal sign. Obviously, the cooling system pressure rises anyway as it warms up, so just few degrees warmer than 'cold' will pump it up a little. If there's any air bubbles anywhere near the heads, then the pressure will rise much quicker as the air warms and expands. So, the system must be properly bled for the test to work correctly. It can only be considered proof positive if there's a significant pressure generated after a few seconds running. There's that 'significant' again. I suppose whether it is or not significant is basically down to personal judgement. You might repeat the test for a little longer while the head temperature's displayed on the diagnostic screen. That way the start and end temperatures are another bit of info. Clearly, if a small gasket leak allows exhaust gas into the coolant when you're driving, there's always going to be 'air' that needs bleeding out.



TC

Well it was definitely slight after the fast test. I have just done a longer fast test for about 100 seconds until she hit 60 degrees and there is hardly any escape of air.

What I did notice on the last test is a sound of liquid running just on start up for a second or two. The sound was from the rear of the dash. Is that significant given this is the first time I've heard it.

Both the heater and air con worked fine

I've idled her until she got to 100 again and Ill see if there is a more significant release of gas tomorrow. If there is what could that signify?

With regard to the exhaust sniff test, if there is not even the slightest hint of exhaust gas from the cap or header is that usually enough to suffice for the test, or should I get a proper combustion leak tester?

Paul

[T-Cut]

Hello Paul. Your results suggest there's still air trapped in the cooling system. The flowing water sound from the dash area is due to bubbles passing through the heater matrix. The heater matrix will still get hot, even if some of the chanels contain air. There are lots of parallel chanels. So, an air-free cooling system is silent. There's a specific routine set down for bleeding the V6, are you following that or using your best guess? The convoluted V6 system means the header tank should be raised during the refill/bleed operaton.

When the engine has cooled down completely, there should be no 'significant' release of pressure when you slacken the filler cap.

TC

[paulh260260]

Originally Posted by T-Cut

Hello Paul. Your results suggest there's still air trapped in the cooling system. The flowing water sound from the dash area is due to bubbles passing through the heater matrix. The heater matrix will still get hot, even if some of the chanels contain air. There are lots of parallel chanels. So, an air-free cooling system is silent. There's a specific routine set down for bleeding the V6, are you following that or using your best guess? The convoluted V6 system means the header tank should be raised during the refill/bleed operaton.

When the engine has cooled down completely, there should be no 'significant' release of pressure when you slacken the filler cap.

TC

Yep TC that was the opening post.

I think I'm following it to the letter, the opening post explain my steps.

What has me stumped is the fact that there is flowing, almost gushing, coolant coming from the bleed screw once I remove the header tank cap. There is no gurgle or splurt you would expect if there was an airlock.

Should I remove the header tank cap before I remove the bleed screw ( none of the guides explain when the cap should be removed) Although that suggests to me it would flow even faster!!

Could it be the fact that I drop the header tank whist I'm refitting the bleed screw, at which time the flow has stopped?( I need both hand to guide then fit the screw)

I cant see how the coolant flows out so fast if there is still air in the system unless I'm doing something wrong

Paul

[SD1too]

Hello Paul,

How did you get on with completely draining the system and refilling with the expansion tank supported so that your hands are free to refit the bleed screw? This should be done whilst coolant is flowing from the orifice.

Your air lock could be stuck in the heater matrix, for example, which would explain why you don't see air being expelled through the bleeding port.

When the engine is running with the expansion cap off, are you getting a steady uninterrupted flow into the filler neck from the small diameter cylinder head bleed hose?

Originally Posted by paulh260260

Should I remove the header tank cap before I remove the bleed screw ( none of the guides explain when the cap should be removed) ...

Refer to the MGR procedure which I gave you Paul. Drain the system, remove bleed screw and expansion tank cap, add coolant until it emerges from the bleeding port without bubbles then insert the screw against the flow.

I think your confusion is arising because you haven't drained the system first.

Simon

[trikey]

If you can hear gurgling behind the dash, you have air in your heater matrix, you need to bleed again to remove it.

[paulh260260]

Originally Posted by trikey

If you can hear gurgling behind the dash, you have air in your heater matrix, you need to bleed again to remove it.

Cheers Trikey

So based on my opening description where do you think i'm going wrong to have to do this for a fourth time ( want to avoid getting it wrong yet again!!)

Cheers

Paul