Engine - Cylinder Head Cover Leak Information
Date: January 3, 2012
Order No.: S-B-01.20/32a
Supersedes: S-B-01.20/32, April 2, 2010
Group: 01
Revision a: Star Diagnosis video information and revised text.
SUBJECT:
All Models with M272 and M273 Engines Cylinder Head Cover Leaks
Field inspections of suspected cylinder head cover oil leaks, have revealed that unnecessary resealing is being performed where the cylinder head
cover is not the root cause of the leak.
In cases of customer complaints of oil leakage, it is essential to determine the actual source. A proper remedy should be applied to avoid repeat
repairs and unnecessary workshop visits (refer to other publications on the subject). For your convenience, a video has been created which outlines
the proper procedure to help identify the source of engine oil leaks. The video is available as of the 11/2011 Star Diagnosis release and can be
accessed through the following path:
SDmedia--> Symptoms/Topics--> Engine--> AR - Localize oil leaks on major assemblies [Model Passenger cars]
The new generation of Mercedes-Benz engines have chemical sealers (sometimes referred to as "formed-in-place gaskets") applied to sealing
surfaces by robots during the engine assembly process. This engine sealing technique called the RTV (Room Temperature Vulcanizing) uses the
Mercedes-Benz A220 2020 Page 81
silicone rubber compound. This precise and uniform application of silicone at the factory insures proper adhesion and a leak tight connection that
very rarely leaks.
During necessary engine resealing repairs, care must be taken in preparing surfaces and applying silicone compound. Do not clean surfaces with any
abrasive materials or sharp tools. Only approved Loctite cleaning spray must be used when prepping engine surfaces (refer to published
documentation on the subject, such as bulletin S-B-01.10129(x)).
Only 1 millimeter (+/- 0.2 mm) thick silicone bead should be applied uniformly to one side of sealing surfaces on a precise pattern (refer to Figure 1
and 2 and / or WIS doc AH01.30-P-1000-08V). A small amount of oil should be applied to camshaft bearings. Sealing surfaces must be assembled
