I have a 93 3500 w/6.5 td 3 days ago started having excessive blowby---pulled oilpan took inspection miror and checked all pistons, no damage and no holes-- vent is also clear!!!! WHAT ELSE SHOULD I CHECK!

Check for broke rings?

No evidence of that without tearing down but all signs seem to show no problem inside cyls.

Cracked head or blown head gasket are also possibilities.





Compression testers exist that thread into the glow plug holes, which can narrow down your search. You can also open injector lines one at a time an look for a big decrease in blowby when the effected hole is deactivated, but you're probably going for the full teardown no matter what's causing the blowby.