Confusion confusion? Just confused..
So I'm back out there bleeding the system again. Got the expansion tank up high, cap off and up to operating temp. At around 212/213 air burps/bubbles will start. It will hold at 213 for a minute or so and the temps fall back to 190. Thermostat opened. The water level falls to near empty. As temps rise again the water level fills to nearly coming out of the tank accompanied by more air. I did this for half, nearly three quarters of an hour. The thermostat always working around 213. But when I put the cap on the tank (with it high or low) the thermostat goes back to opening 220 and etc..
So I'm thinking somehow there is pressure being induced into the cooling system. Since the previous owner had overheated the engine (not knowing how hot or how long or how many times...) I'm guessing my luck has run out. I have the valve cover today to inspect the plugs and get a look at the pistons. Pistons all have carbon on them. No clean tops. Plugs are looking normal and all consistent. Before I pull the head I didn't know if anybody had two cents to throw in. My mental bucket is getting empty.

 

OFF with her HEAD! A little to dramatic?
No real signs of gasket failure. Only as I pulled the head off, the one layer of the gasket stayed to block. I mean it didn't even peal apart from the other half. Not sure if that is something even stating.
More importantly, no cracks between the valves. Tomorrow I'll clean the head and put a straight edge to it.

 

Think I'm looking at a warped head. There's .006 between cylinders 3&4, .005 between 2&3, .004 gap along the back of the head. Think I'll be calling machine shops tomorrow. The play in the valves makes me wonder about the guides, but all will be known soon enough...
I'll report back after reassembly.

 

Got the head back last night. All back together and still can't get air outa the coolant system. Getting kinda frustrated. Maybe I'm bleeding it correct?
The machine shop took .009 off the surface and did a valve job. The miss at start up is gone.. But the coolant level in the expansion tank will be at below minimum level and push up to the top. I've start to try a new way to bleed it. I got a half a Pepsi bottle stuck in the the tank. When the temp gets to 210 and it's time for the thermostat to open, the water level rises and comes up the bottle, burps and air bubbles come out. Temp stays a 212/213 and starts to come back down, as well as coolant level. I did this process for 2hrs last night.
If I put the cap on and go for a drive, the temps cycle between 221 to 230. I really don't want to have to pay someone to burp the system , but it's getting there. Is there anything else that can be inducing air into the cooling system. Like I stated, I've replaced the : coolant flange, j-plug, thermostat, expansion tank and water pump. There is no leaks, only what I believe to be air in the system.
????????????

 

Sorry if I'm bumping an old thread... I've had the same issue and all threads I've searched for do not have end solution response.

Same sob story here:
a4 1.8 (AMB)
Already changed
Headgasket/head/waterpump and lastly thermostat (twice)
Also verified thermostat in hot water and It opened, at a very high temperature.

Same things is happening when it is in the car, car heats up and builds pressure in coolant system.

Funny, I bought the car thinking the waterpump was gone and unfortunately, i'm in the middle of this mess now.

Ever find a solution??

Cheers

 

This can't be good.... so I'll just go into further detail.

Starting to think somewhere down the line, there is a blockage in coolant system or a hose is hooked up wrong and started this issue.

Should there ALWAYS be coolant coming out of expansion tank return line (small line on front of tank).
Before thermostat opens, there is none coming out
when thermostat opens, there is a slow steady stream

This is starting to look like a flow issue of sorts