Hey, i have a 1.9 tdi with a 5-speed manual... At Norwegian roadspeeds (80kph/50mph) i just cant decide if i should use 4th or 5th gear... When i reach hills, and the cruise-control starts to accellerate, the engine shakes and rumbles quite a bit, so i tend to keep it in 4th... It lays around 1400rpm in 5th... Should i keep driving in 4th to prevent soot in the turbo and particle filtre?

5th gear at 1400rpm is fine for driving on flat without accelerating but you should change down to accelerate or climb hills where the load on the engine increases.

 

This should, as you say protect the turbo and DPF from clogging and also save wear on the DMF and gearbox.

 

Also make sure you drive it a bit harder now and then using more revs to keep everything cleared out.

Seconded; if you're hearing the engine "lugging" like you describe, you'll give the engine and clutch an easier time if you change down a gear.

Thirded! 

 

When I got my wife going on the Superb (manual) diesel (she had only driven petrol before) I told her if anything feels like the onset of a stall (chugging, vibration) then change down a gear. I don't care what the "suggested Gear" display is saying (if you have that - it suggests changing up too early for the good of the drivetrain IMO) and I don't care if the Cruise control is on and I don't care if the car is "managing it".

 

I think the basic rule with cars always applies - if it doesn't feel right then it isn't right. 

 

Like Phil-E and Ken say, give it a burn from time to time. I'd define that as making sure that at least once a month, you make sure the car has been driven when warmed up for 25-30 minutes with the RPM over 2000. I'd also take the opportunity to let the RPM get over 4000 when joining a motorway or similar (i.e. drive it hard and blast some junk out).

Thanks guys