Audi S3 coolant "boiling", misfires, coolant in oil

[null1337]

Hello guys,

Audi S3 2015 CJX, 90k kilometers mileage.

I'm running out of ideas.
It started with water pump leak - replaced.
While bleeding coolant system after replacing water pump thermostat housing we noticed there is problem with bleeding and water is "bubbling" (video).
My mechanic said it's normal behaviour, because of pressures etc. I didn't quite believe in that, because there isn't any "boiling" in my father's A3 2.0 tfsi and even my friend's same S3.
I was trying to make test for CO2 in coolant, but it was impossible due coolant reaching too fast to the tester.
Engine was sometimes running a bit I did basic diagnosis in VCDS - it showed misfires on all 4 cylinders. Few misfires after 10 min on idle and about 10-20 misfires on each cylinder after hard 1 km ride. Also there was something which looked like coolant under oil cap (picture) - mechanic said it's not coolant (then WTF is this).
Head was reassembled - no signs of wear or anything on gasket and cylinders. Head was checked under pressure with hot water for cracks, then planned and assembled. Coolant system was checked under air pressure.
Result after head regeneration - same problem with boling coolant, no misfires on idle, no coolant in oil.
At least that's what mechanic said. There wasn't test drive yet, because car was on summer tyres. I am picking it up tommorow and will check by myself on road if there really aren't misfires and no coolant in oil.

Car has no problem with power, no white cloud from exhaust. Oil coolant radiator wasn't checked yet, because he said that if it was damaged then oil would be in coolant, because of much higher pressure of oil. Bottom of the engine block wasn't checked too.

I'd appreciate any ideas why is this happening & what else could be checked.

Video

[MikTip]

After driving...the spark plugs need to be removed and look down into the cylinders...the piston tops...see if their is coolant. If you have a boroscope even better.

If coolant is found then the head is cracked...usually in between the valves.

(Oil coolant radiator wasn't checked yet). I would replace it...to eliminate it being the cause.

Also the turbo charger share oil and coolant in the same place...might be that...

[null1337]

I've forgot to mention - compression is fine. As I wrote in post - head was checked for cracks with some special fool with compressed hot water, it's straight. Block is straight too.

[MikTip]

I've forgot to mention - compression is fine. As I wrote in post - head was checked for cracks with some special fool with compressed hot water, it's straight. Block is straight too.

Change Oil coolant radiator

[null1337]

Change Oil coolant radiator

But it can't cause water boiling like this, is it?

[MikTip]

But it can't cause water boiling like this, is it?

At this point you do not know what it is...you do know the oil coolant radiator wasnt checked or changed. If you change it.. its eliminated from the equation.

I also wrote it could be the turbo....

[null1337]

Car is probably after chiptuning. I've discovered turbo is pumping almost 1.6 bar (23 psi) in peak. I'm going to restore ECU to stock tommorow. Also EPC error with turned off 4th cylinder (too high pressure) showed up. Probably due too many misfires or knocking. Additionaly error about blocked auxiliary water pump showed up yesterday, but it may be related with me changing HVAC hot country settings from cold country to normal.

[MetalMan]

I've forgot to mention - compression is fine. As I wrote in post - head was checked for cracks with some special fool with compressed hot water, it's straight. Block is straight too.

On a different Audi platform, the B6 A4 1.8T, cracks in the cylinder head were very common (cylinder head code AMB). My B5 A4 1.8T with cylinder head code AWM even developed a crack between cooling jacket and valve seat. The effects of this crack were not noticeable until the engine was HOT - such as driving on the highway for 20+ minutes. Then in that circumstance if I went full throttle the crack opened up enough and combustion gases pushed into the cooling system... which pressurized the cooling system. On long road trips in hot weather and mountain driving the car would overheat. But cooler weather and shorter trips this wasn't an issue.

Also the car had EXCELLENT compression at 130k miles. I don't think pressure-testing my cylinder head as yours was would have revealed the crack.

[null1337]

On a different Audi platform, the B6 A4 1.8T, cracks in the cylinder head were very common (cylinder head code AMB). My B5 A4 1.8T with cylinder head code AWM even developed a crack between cooling jacket and valve seat. The effects of this crack were not noticeable until the engine was HOT - such as driving on the highway for 20+ minutes. Then in that circumstance if I went full throttle the crack opened up enough and combustion gases pushed into the cooling system... which pressurized the cooling system. On long road trips in hot weather and mountain driving the car would overheat. But cooler weather and shorter trips this wasn't an issue.

Also the car had EXCELLENT compression at 130k miles. I don't think pressure-testing my cylinder head as yours was would have revealed the crack.

That's interesting. The thing is that my coolant is "boiling" when engine is cold too.

[MetalMan]

That's interesting. The thing is that my coolant is "boiling" when engine is cold too.

Sounds like then a crack in the cylinder head isn't likely.

I'm going to propose some additional test ideas:

• Leak down test - and check to see if the cooling system pressure increases while combustion chamber pressure decreases
• Cooling system test - I didn't see this mentioned, but have you pressure tested the cooling system? I wonder if there might be a "leak" that is actually sucking in air near the water pump, where the system might be under more of a vacuum than pressure.

Also I agree that the oil cooler ("oil coolant radiator") is not likely an issue. As you noted the oil is at a higher pressure and when it fails, oil will be in the coolant and not coolant in the oil. (had this problem also on my B5 A4 1.8T)
Turbo could be an issue though, so I'm curious if going to stock ECU tune changes anything.

[null1337]

Cooling system was tested for leaks under pressure.

Car was tuned. I've reverted soft to stock today and misfires are gone. Tuner discovered other related problem. There is up to 6* timing angle retardation on every cylinder...