Due to the death of the GTD, I am now the owner of A SEAT Leon TDi, (a spanish made MK4 Golfish thing) which has the 110hp ASV TDi engine. This was the start of a year long battle of the bubbles.
Lots of massive 2 inch long air bubbles scooting along the intake line, from filter to pump.
new fuel lines.................................................................................bubbles.
new mann filter...............................................................................bubbles.
new genuine bosch tempvalve and "o" rings..................................bubbles.
Sulk a bit.........................................................................................bubbles.
Check fuel tank pick up, clean as whistle........................................bubbles.
Smear gobs of blue hylomar around all fuel line joints....................bubbles.
Smear gob of hylomar about the swage on the mann filter............bubbles.
Check fuel tank breather................................................................bubbles.
Sulk a bit more, this battle has been going on for about a year
Genuine SEAT temp valve (Bosch) on Ebay for £5, buy & fit, not expecting much......................result?
NO MORE WRETCHED BUBBLES and an extra 6 mpg.
So don't assume that that new genuine bosch thermo valve is good out of the box.
Good luck with your Battle of the Bubble.