I have a 2004 diesel Prado. 302,000km no catch can and no problems with engine. Always serviced by Toyota

Lets first of all go back in engine history well before the PCV valve which became law and the follow on of how we as vehicle engine designers actually dealt with engine Blow By... yes that is what it was actually called.
Well, all the engines had a level of engine Blow By and this was disposed from the crankcase of the engine by what was called a Draught Tube.
This tube was generally fitted in the Rocker Cover or the Side Plate of an engine, depending on the configuration and the subsequent fumes that were emitted from the engine were disposed into the atmosphere. via the draught tube.
This draught tube had an angle cut onto the lower extremity of the tube which provided an angle which actually by way of a small vacuum allowed the negative air pressure created behind and to the rear of this tube to actually draw the fumes from the crankcase (Sump) and reduce the crankcase of pressure.
As time went on we as a society of people who needed to provide cleaner air to our fellow man our collective authorities decided that this system was not conducive to us all breathing clean air so low and behold the PCV valve was invented to enable the oil fumes to be recirculated back into the the intake manifold.
We as an engineering society were actually fortunate that when this big change was happening we were also developing better manufacturing practices with the internal combustion engines and their ability to restrict pollution of the air.
Lets face it, the big deal with most governments was lets sell clean vehicles.
That is not a problem lets sell clean engines...
From this come what we have today...
An engine thats use is only taken as an average of how it it is actually used. A clogged engine does not function as it should but unless an authorised inspector says that it is nor acceptable then it continues to operate as a pollutor.

We have vehicles that are only driven for short distances and if they are diesels then any Toorak Tractor, or lesser vehicle will have an engine coking problem.
Tradie vehicles that only travel short distances may coke up...
Vehicles that are beginning to show signs of engine wear will coke up.
Vehicles that have a faulty or out of service PCV system will coke up.

On our forum, fortunately many vehicles are driven for long distances per day and over the standard life may not show any problems but to generalise is at the least, dangerous as a worn engine or a new engine that is not run in correctly or just the change of use of an engine in reasonable condition may create a problem to the owner.
My original post, even though it copped poo poo from the OP was my explanation of why I fitted an oil Catch Can.
My mistake in my post was that for the first 18 months my wife only used the vehicle as a shopping trolly.
I was fortunate that this use resulted in no problem but as I had fitted a Provent Oil Catch Can from new I had no way off assessing if the non fitment may have caused me any major costs with the de coking procedure of my engine.

-- Edited by Dickodownunder on Tuesday 22nd of January 2019 08:58:10 PM

-- Edited by Webmaster on Tuesday 22nd of January 2019 09:25:15 PM