I never messed with mechanical tensioner because i don't want to ruin something bacause of improper tension.

Hydraulic ones are so simple....no adjusting needed.

Just came across this...might be helpfull:
https://www.underhoodservice.com/volvo- ... tensioner/

If water pump is original and not leaking...leave it alone. I've been occassionally hearing a "groan" noise from the passenger side when the car is in motion but not yet warmed up. I was concerned the water pump might be failing... Water pump is Aisin btw. Timing belt is OEM. The oil cool...

As it is a turbo 98 year, chances are the groan, is when it is cold. The source is probably the oil cooler thermostat. The make weird noises when they get old ( a bit like me apparently!).

Neil.