Noise from hydraulic tappets ?

[Daniel]

My Thema S2 V6 gives a "ticking" sound from the engine room and it becomes louder if the oil temperature is higher than 60 degrees.

My garage told me that the noise is caused by one or two hydraulic tappets and these have to be changed. I have also asked another garage which has specialised to engine repairs and they said noise from the hydraulic tappets can be caused by the oil, too.

The car has run 138.000 km so far and I use 10W-40 part-synthetically oil. Now I wonder if I should change to full-synthetically 10W-60 oil (quite expensive).

Has anybody experience with this problem ?