Mk3 VR6 gurgling/air bubbles from Heatercore

[Mustillo]

Hi all,

About a month ago I decided to do a coolant flush while replacing all of the coolant hoses. I did a thorough flush using a hose and flush additives. After installing new hoses and bleeding the system I have noticed this odd air bubble sound which I am assuming is coming from the heater core, just below the dash, above the pedals.

Just recently I noticed my gauge had stopped working (stuck on 70), I had a fault for the sensor (implausible) and also my bottom radiator hose was never getting hot and the thermostat was stuck closed. I thought this was an explanation to why air bubbles were trapped in the heater core as they were not circulating around the system...

So today I flushed the coolant and also replaced the thermostat & seals. I then pressure bled the system using a Snap-on tool, bottom hoses collapsed it sucked up 4.5L of G12 and the rest with demineralised water.

1. Left the cap off ran the car for about 30 minutes (Guage hit 90 degrees, fans were on, heater was heating & bottom rad hose was hot)
2. Revved it now and then
3. Pinched the top and bottom hoses a couple of times,

But that damn annoying air bubble noise is still there?! I sure as hell hope it's not the heatercore that is on it's way out... Previous owner had it done which I was relieved to hear.

Any ideas? I have read that this gap of air can cause condensation leading to a rust hole in the heatercore...

Thanks in advance!

[Martin]

Make sure the car is level

You installed the thermostat with the pin hole at the top?

Make sure the heater is on max hot during the flush and warm up

After running the engine and the temp gauge reaches ~90 turn off but leave the ignition on
The electric water pump often kicks in and helps the bleeding process

[Mustillo]

Thank you,

Make sure the car is level

You installed the thermostat with the pin hole at the top?
Yes defiantly, didn't want to make that mistake

~90 turn off but leave the ignition on
The electric water pump often kicks in and helps the bleeding process

I'll try this tomorrow, just leaving the electric water pump running.
I have read that some people unbolt the coolant bottle to lift it higher?

Just seems a bit strange that air can still be in there

[Mustillo]

Make sure the car is level

You installed the thermostat with the pin hole at the top?

Make sure the heater is on max hot during the flush and warm up

After running the engine and the temp gauge reaches ~90 turn off but leave the ignition on
The electric water pump often kicks in and helps the bleeding process

Yes thermostat air escape hole was aligned to the top as best as I could.

Thanks

[Martin]

Just seems a bit strange that air can still be in there

Some cars bleed easy and others can be a real pain

[Martin]

Starting it from cold with the water bottle cap off and turn off by the the time the engine reaches 90 deg

[Mustillo]

Starting it from cold with the water bottle cap off and turn off by the the time the engine reaches 90 deg

I ended up poping off the top throttpe body hose, connected a temporary hose to the throttle body back into the bottle then ran it, air came out of the heater core feed hose!

Seems to be better but the water pump has decided to screw up, so I'm going to have to do it all again while replacing it

[Martin]

I ended up poping off the top throttpe body hose, connected a temporary hose to the throttle body back into the bottle then ran it, air came out of the heater core feed hose!

Seems to be better but the water pump has decided to screw up, so I'm going to have to do it all again while replacing it

Well done and good thinking - typical that the car would bite back