ISM, ISMe, and QSM11 – Crankcase Gases (Blowby) Excessive

Symptom Tree  t027

This is symptom tree t027
Cause Correction

Crankcase ventilation system is plugged

Check and clean the crankcase breather and vent tube. Refer to Procedure 003-002 in Section 3.


Centrifugal bypass filter is malfunctioning

Disconnect and plug the air supply line to the filter. Check for blowby again. If blowby is within specifications, repair the filter. Refer to Procedure 007-012 in Section 7. Refer to the OEM service manual.


Turbocharger oil seal is leaking

Isolate the turbocharger to determine if the turbocharger seals are leaking. Refer to Procedure 014-010 in Section 14.


Air compressor is malfunctioning

Isolate the air compressor by disconnecting the air inlet and outlet lines. Refer to Procedure 012-003 in Section 12. Check blowby. If blowby is within specifications, rebuild or replace the air compressor.


Rocker lever housing or rocker lever housing gasket is leaking intake air into the crankcase

Inspect the rocker lever housing for cracks. Inspect the gasket for tears and breaks. Inspect the gasket sealing surface for scratches and cracks. Refer to Procedure 003-013 in Section 3.


Cylinder head valve guides are excessively worn

Check the valve guides for wear. Replace the cylinder head, if necessary. Refer to Procedure 002-004 in Section 2.


Cylinder liner, pistons, or piston rings are worn or damaged

Check the pistons, piston rings, and cylinder liners. Refer to Procedure 001-043 in Section 1, Procedure 001-047 in Section 1, and Procedure 001-028 in Section 1.

Last Modified:  11-Oct-2010