Coolant question (again)

Madman1886 · 13 Jun 2025

Afternoon peeps,

As per my last post, I've been having some coolant issues after changing 90% of the pipes during the winter. After following the procedures outlined (vacuum fill and then burping as required) my car still popped a front pipe after the first reckey run. So I've fixed that and refilled and burped again. Took the car a run earlier and she went fine, no warnings or fluid loss, temp never went above 80. However, when I parked up I popped the hood for a look and noticed the coolant level just below the min and the burp clip wouldnt go back down when replaced in normal posistion. I let it cool a bit the slowly removed the cap, usual release of pressure and coolant went back upto max. Is this normal, or is it a sign of an airlock in the system. Any help would be appreciated. Cheers.

gizlaroc · 13 Jun 2025

You need someone to rev it to around 4000rpm with the cap off, and ideally when "warm", around 40-50ºc, don't go higher, well you can get higher, but don't take the cap off if it is higher than that.

Set climate to max temp to get the heater matrix in the loop, then get it up to that 40-50ºc temperature with the cap off and start to rev it, you will probably see the level drop as you rev it, rev it up and down a bit and try and hold the revs at a steady 4000rpm for a bit, or 3000rpm if 4000 is too loud and annoying neighbours, keep doing it for while and you should push any air through, and thus the level will drop, after 10 mins or so when you think you have got it out, put the cap back on, and put it on with still being revved to 3-4000rpm.

Now check it again over the next 4 or 5 drives and do the same if needed.

Madman1886 · 13 Jun 2025

Had the wife doing that, and I filled it as she sat at 3k revs, however as she let the revs drop a big gush of coolant overflowed out. Car was nose down as well. But I've just got a horrible feeling there's still air in there.
I'll give it a few runs and see if it settles down a bit. Thanks

Luddite · 13 Jun 2025

I wonder, is it desirable to be sure that the heater is calling for heat, to ensure the heater matrix is in circuit when burping the system..?
.Just thinking in type.

gizlaroc · 14 Jun 2025

Yeah definitely. Good point.

I will edit my post above to include that.

Mac996t · 14 Jun 2025

Luddite said:
I wonder, is it desirable to be sure that the heater is calling for heat, to ensure the heater matrix is in circuit when burping the system..?
.Just thinking in type.

Thats not necessary in either the 996 or 997 as the coolant flows through the heater matrix 100% of the time, there are no valves in the heater pipes as there can be on other cars!

Mac996t · 14 Jun 2025

There's so much written about how to bleed the coolant system on these cars.

The key thing to know is that most of the air stays in the system until the thermostat opens, and once open the coolant still doesn't flow everywhere unless you rev the engine the get the waterpump generating some pressure. The next problem is that if you then let the revs drop to idle the pressure you've just generated pushes the coolant momentarily back into the coolant bottle which then overflows. You can stop this by putting the cap back on while the revs drop then take it off again. Keep adding coolant until it will take no more even when reving, and all the pipes are hot and the engine is at normal temp.
This will have got about 97% of the coolant in.
But you're not finished yet there will still be small pockets of air as not all of the bleed points are at the high point so next you need to drive the car with the burp valve open (cap on tight) while turning hard left and right and accelerating and braking. This will allow the last of the air to make it back to the expansion bottle. You should find this last bit will allow you to add about 0.5 litres then the level should stay constant. Also as soon as the burp valve pin stays up by itself when the engine is warm you can then put put the burp valve handle back down.

Madman1886 · 14 Jun 2025

Thanks peeps, appreciate all the help. Just to point out, had the heating on high and full blast, cars heating up no problem. I'll do it again with the revs at 3k and before she let's the throttle go, ill make sure the caps on tight. Thanks