Since my engine has twice been so badly gunked up it wouldn't start, I installed an inexpensive catch can. Installation was easy and only took a few minutes. The can is actually a filter, and was installed in the tube after the PCV valve and before the intake manifold. The can fastened to the airfilter box.
I had a hunch that possibly blow-by was contributing to the reoccuring gunk formation, that being reason for trying a catch can. During the timespan between both gunked-up occurences, the valves were impecably clean, that verified by endoscope. The car has about 100 000km (60 000miles) on it, and the compression is a bit lower than normal ever since the first gunk "repair" at the Mitsubishi dealer. It needs no extra oil between oil changes. The gunk covering the intake valves forces them to remain open, causing massive compression loss and thus no starting possible.
For that story see thread: https://mirageforum.com/forum/showth...ar-won-t-start
During repair when the intake manifold was out of the car for gunk clean-up, I notice that behind the throttle, the manifold was perfectly clean inside. However on the cylinder head side, the inside of the intake manual was coated with a black, oily, gritty, carbon-like substance, some sort of combustion residue. Near the middle of the intake manifold is where the tube from the PCV valve merges into it. From there on, the inside of the manifold is coated with residue. Before that tube, the manifold is clean. That was the reason for trying a catch can. It might not stop gunk coating the valves, but can't do any harm.
Test results:
The catch can has a very fine brass filter inside for catching droplets from the blowby mist, and it does collect more than I thought.
UPDATE after one week:
The catch can pictured below catches oil at the rate of about 3ccm every 1000km.
This model will collect about 12ccm until I call it full. That is the point when the caught oil begins to touch the fine brass filter.
In other words, only about 4000km and the catch can needs emptying out. Therefore I ordered a similar but inexpensive bigger one for a few bucks.
This is the catch can originally bought:
https://www.ebay.de/itm/Car-Universa...8AAOSwwFlfBvnh
Here some pix how it was installed. The original tube that was on the PCV valve was not shortened, it connects can output with manifold. A new piece of tube a few cm length (in medieval: "inches") was put between PCV valve and the intake of the can. Important: although the can and tubes have no real pressure to withstand, they absolutely must be airtight! If not, the engine will not idle properly or may not start.
Btw, there is a TSB about non-starting engines where the rubber tube slipped off the PCV valve.