TDI HEAD

[dero]

I have a problem & need some qualified help
300TDI is pressurizing the expansion tank when running , happens faster under load .
cooling system seems to be working well until it gets an air lock in the t'stat housing area , low water alarm goes off , bleed the air out & all is well until it get another air lock[ not long , less than 5K ]
Seems to be head gasket type problem . Mechanic tested the expansion tank for combustion gas , tester shows no problem . Tested with engine hot & revving until the tank overflows .
Removed the head , no obvious sign of gasket failure , head has gone off for pressure test .
I can't think of anything other than combustion that could push air into the system .
Any advice would be greatly appreciated .

[Blknight.aus]

DEatd/clogged Vacutator valve and a clogged radiator can do similar, and it may be a small leak somewhere else letting the system pressurise out letting the head cook.

Fan VC and expansion tank cap are also rans.

[dero]

All the above checked out ok , and no sign of a drop of leakage any where .

[loanrangie]

Welch plug at the back of the head OK ?

[dero]

Yes.

[dero]

DEatd/clogged Vacutator valve and a clogged radiator can do similar, and it may be a small leak somewhere else letting the system pressurise out letting the head cook.

Fan VC and expansion tank cap are also rans.

DEatd...Presumably, Do Everything , attention to detail .
The final piece in the puzzle seems to have been an almost imperceptible leak at the top of the radiator core , must have allowed air into the system without any sign of leaking coolant . took a lot of finding .
Your advice has always been good , so I persisted with the attention to detail , and found the leak .
THANK YOU . Seems to have solved a MAJOR headache .

[Blknight.aus]

DEatd...Presumably, Do Everything , attention to detail .
The final piece in the puzzle seems to have been an almost imperceptible leak at the top of the radiator core , must have allowed air into the system without any sign of leaking coolant . took a lot of finding .
Your advice has always been good , so I persisted with the attention to detail , and found the leak .
THANK YOU . Seems to have solved a MAJOR headache .

typonese for Dead, but other than that,

yes, Do Everything, attention to detail is what I ment..

of course, there are two secrets to every good mechanic,
1. Ass beats class, every time. And, my personal insistance
2. "My one true talent in life lies in keeping people guessing where my skill ran out and my luck began."

I'll let you work out where on the line this one fell.
(hint: both answers are correct and both is an acceptable choice)