How much blow by is too much?
 

I went and looked at a couple Diesels yesterday. One was an NA 300D that had some blow by that was whitish in color, not that much but I noticed it, I then proceeded to check out a turbo 300D that also had blow by but it was blue, and about the same amount as the NA motor. I wonder if some is OK or not?

Let engine warm,open hood.Losen the oil cap if it shoots off maybe bad,if it rattles ok.Note: valve adjustment can improve things,and hose routing to burn blow by gases can affect cap.

my buddy told me that if you can shut the engine off quickly by holding your finger over the valve cover vent, it's got a decent amount.

any truth to that?

I've heard that too.

From what I understand, attempting to shut the car off via plugging the offgas line is not good for the engine.
Don't think a valve adjust will affect blowby, since it is plain and simple, gasses getting by the pistons. So all lower end of the engine.
Blowby is not the be-all end-all in terms of engine health, but I always check it when looking at a car, always after it's been warmed up.
If it blows the cap off, I'm wary of that engine. Saw a 113K mile coupe that barely moved the cap at all, and a wagon with 300K where it blew the cap right out of the engine bay.

Answer
 

Run away diesel, why does it happen?
http://www.peachparts.com/shopforum/showthread.php?t=101404





Have a great day.

MB made a tool for measuring blowby. I assume there are limits related to that tool.
Some years ago, a thread was started on this forum in which blowby was measured in the number of seconds the engine took to pressurize a 30 gallon trashbag. Not a bad comparative process in my view. Here's the thread:

http://www.peachparts.com/shopforum/showthread.php?t=193602&highlight=blowby+gallon

Pinching off the PCV hose and pressurizing the crankcase has very limited value because it presumes that all crankcases have equally intact seals. They probably don't and probably won't once the crankcase is pressurized.