This is a debate that will continue ad-infinitum. I'm guessing that if an engine is already extensively coked then the removal of all of it could lead to sealing problems.
However, if coking is controlled by virtue of good operating conditions (ie. quality fuels, good maintenance and not too much short distance driving) then it's best to keep things clean.
I've never yet heard anyone say that it's a good idea to skip a couple of services, use the wrong grade of oil, fill with poor fuel and drive stop start for five years in order to build up a healthy deposition of carbon and other associated by products of poor combustion.
I also think everything has changed since my day, better fuel, fuel injection, ecu controlled, and better engine designe, when was the last time you needed to take the head off to do a de-coke
I asked about that two, Could just be how that engine is. Should be no reason for the drop off unless they had some air left in the lines or did not put a vent hole in the tank.
Re: Alcohol/water injection turbo diesels. 
Linear Mode
