Cooling system air lock problem

[Clarky_X]

All. I seem to have an air lock in my cooling system.

Symptoms:
Looses water at between 1/4 and 1ltr / tank (200 miles)
When water is low, gurgling heard in the dash, heater matrix.
Water is very frothy in filler and header.
Header tank is full.

I had a new rad less than a year ago as I lost a lot of water due to a leak. When I had the new rad I put a new TRD rad cap on (1.3 bar).

I am using Halfords coolant for older cars, mixed 50/50.

I think the coolant loss is due to an air lock forcing water into the header, and overflowing out the tube onto the road.

I bled the cooling system several times on Friday. I couldn't find the engine bay bleed valve (AE101 GZE) so just used the service hoses on the rad bleed and heater bleed valves. The rad bleed valve just leaks when open so I had to open it to get water into the service hose then close it just to stop pouring too much coolant down the drive. Every time I closed the valve, each turn reduced the water level in the service hose.

I bled it through 3 times and obviously the level in the filler neck kept dropping, probably due to the leaky rad bleed valve. I then realised that I had the heater set on the coolest, so put it up to full heat and bled another 3 times. Still the level in the filler neck kept dropping, again probably due to the rad bleed.

Every time, the coolant was frothing in the neck and frothing in the header tank.

Do I still have an air lock? Is this another problem?

I am yet to take it out on a test drive, so maybe time will tell, but I was expecting at least the frothing to stop.

I have not flushed out the heater matrix with a hose yet. Thought I'd try the bleed first.

Any help welcome.

Regards
Stephen

[MartG]

Frothing is quite often a sign of a blown head gasket ( possibly caused by low coolant when you had a leak ), with gases from the combustion chambers being forced into the coolant

[Clarky_X]

Well, I did initially think head gasket when I started losing water, but my garage man said its not as it would be pouring white smoke out the exhaust if it was burning coolant. But I suppose if the compression is forcing air out, it won't be able to let water back into the chamber?

[MartG]

Yep - it depends on exactly how the HG has failed - sometimes they fail in a way that water is sucked into the cylinders and steam comes out the back, other times they fail so gasses are forced into the coolant and overflows the header tank