1.8t Air Lock / Cooling system issue

[spellmaster]

Sooo, I'm back in the Audi club. I snapped up a 8E 1.8t (190PS, not sure what code) A4 Avant spares or repair, apparent circulation problem.

I guessed that maybe the previous owner may not have known about the bleed hole in the heater matrix output pipe. However, after a few sessions bleeding it seems that it is indeed suffering from air locking far more than any of my previous B5's (1.8/2.8/S4).

So heres some details:
- 138k on the clock, runs nice, good progressive power.
- Air lock prevents water flowing out of the heater matrix so no warm air is felt unless driving is aggressive. (lead me to believe it was the matrix)
- The car gets nicely up to 90 and stays there, fans in the rad kick in too.
- Cooling system pressurises, quickly. And stays that way for a long time, still pressure enough in it the next day to squirt you from the bleed hole.
- Coolant looks a little brown.
- Compression in cylinders (aprox), thought maybe cracked head but these numbers look ok 1 a little on the low side perhaps?:
1 : 166psi
2 : 181psi
3 : 188psi
4 : 174psi


Whats already been done, an impressive amount by the last but one owner (an audi tech apparently):
@ 135k
Head gasket, and everything associated with it gasket wise.
Timing Belt
Water pump
Thermostat & coolant
Thermostat - Flange
Oil Filter, Oil
All genuine parts (£500 worth in total)

So today i replaced the Heater Matrix & seal kit (genuine £150ish), so far after one test drive 20miles, i still have varying temperatures, ranging from none to lots. heavy load brings on heat, but high fan speeds kill it off. After the car had sat a while tonight i managed to get more air out of the system via the hole in the matrix outlet pipe so will take it on another drive tomorrow and see if the heat is more consistent.

ho hum. if i cant bleed it then i'll have to consider something more sinister is going on. I did try my block tester immediately after getting it home, it didn't go yellow. Perhaps i'll give it another try and see if that reveals anything. I also see these engines suffer with cracking on the cylinder head, i guess its possible that its in the early stages of cracking through to the cooling system, but no water is shooting out of the bores during compression testing.<br>

Any one else on here have a hard to bleed audi 1.8t? i have seen some people post that they need to bleed in other locations like the water temp sensor and rad top hose?

[pauldazzle]

Do you have flow from the headertank return pipe?

[spellmaster]

A little more testing today, results are bad Given all the work that has been done and how well the engine is running I'm thinking it could be a crack in the head

[zollaf]

fluid goes yellow, off with the head and have it tested. you might be lucky and the gasket was replaced before without a skim but you won't know until its apart.

[spellmaster]

Yea I'm hoping they just changed the gasket without a skim, what a waste of genuine parts

[spellmaster]

Took the head off this morning and found the head has cracks in two cylinders, darn.



One seems to be letting oil, the other I guess water. Anyhow this head is junk, fortunately the valves can be reused in another 20v head I already have, shame it's an early head without auxiliary air pump port, or I could have used it for this..

Looks like this ain't the first head this engine has had either as the engine code is missing from the top

[zollaf]

nice, well found.
shame, but at least you know the fault.
my head is cracked in 2 places but its ok and not done anything in 20k miles.

[spellmaster]

Yea had considered getting it pressure tested to see if there was a problem with the cracks, I guess some can be benign, however when I looked at the bores you can see oil is defiantly getting through cyl 2, also explains why the filler cap jumps up at you!

[zollaf]

deffo quite conclusive. no sign of the new head gasket leaking then i presume.

[spellmaster]

Hard to tell it was so new! Couldn't see any tell tail markings, I don't think it was though unless the issues with the cooling system created some really hot spots and warped the head.

However the car ran so well that I think the cracks are the culprit, any gasket issues normally result in some exhaust smoke or poor running