Hi all,

I have just changed my 2.0 octavia for a Superb 1.9TDI PD , and have sorted the VW505.01 oil

questions out. Can anyone tell me if a PD engine has anything in common with a CRD engine or any pros and cons with either?

Thanks Roger.

(First time wiith a diesel and just wondering what I have got !!!)

Not really anything in common with a common rail other than its an advanced diesel engine.

The distinguishing feature of both the common rail and the unit injector (PD in VAG speak) diesel engine is the use of very high injection pressures.

Both systems will generate pressures far in excess of those achievable with a standard inline or rotary fuel pump with the result that greater power outputs can be produced at a lower exhaust smoke level. This is mostly due to improved fuel atomisation and the more precise control of injection timing possible with a shorter fuelling duration for a given volume of fuel per shot. Of the two systems, the PD can still achieve higher pressures (approaching 30,000 psi) than a common rail engine but the control of such features as pilot injection is more difficult.

This means in very rough terms that for a given smoke level, the PD will produce more power for less fuel, but the common rail engine can be more refined because a controlled pilot injection will give a "softer" combustion with a more well defined cylinder pressure rise.

This is necessarily a gross simplification which takes no account of developments such as DPFs (which are detrimental to engine performance) but basically if you can stand the noise and roughness, a PD without a soot filter is amongst the most efficient diesel engines ever produced.

rotodiesel.

Thanks both for your replys, Its all clever stuff under that bonnet. I just hope it keeps working !!!

Roger.