Gasket for oil sum

An oil sump gasket seals the oil sump to the engine block and prevents engine oil from leaking out under pressure and thermal stress. In MAN and Mercedes trucks, buses and vans, this seal is essential for maintaining a stable oil level, a clean engine environment and the protection of underlying components such as the crankshaft, connecting rod bearings and oil pump. Oil sump gaskets are available as moulded rubber-elastomer gaskets, multi-layer metal seals, cork-rubber gaskets or liquid sealants applied to specified mounting surfaces. The correct type, the position of sealing strips and any integrated sealing lips vary according to the engine variant.

An oil sump gasket must always be selected based on the vehicle chassis number. Visual comparison or selection based solely on the model name is never sufficient. Even within the same engine family, there may be differences in sump shape, fastening pattern, oil pan construction, sensor positions and the use of front or rear crankshaft seals. This is relevant, among others, for MAN D08, D20, D26 and D38 engines, as well as Mercedes OM 904, OM 906, OM 457, OM 470, OM 471 and OM 473 engines.

On heavy-duty diesel engines, the oil sump often consists of a cast aluminium upper sump section and a steel or aluminium lower sump. The sealing arrangement may then include separate gaskets, O-rings for oil passage connections and liquid sealant at specific transition points. Also pay attention to the fit around the flywheel housing, timing cover and any oil level or oil temperature sensors. A gasket that appears identical may still seal insufficiently due to differences in bolt spacing, sealing lip height or material hardness.

A defective oil sump gasket generally causes visible engine oil leakage along the sump flange, oil deposits on the chassis, contamination of protective panels or dripping after the vehicle has been parked. In more serious cases, the oil level drops between service intervals, an oil smell develops on hot exhaust components, or the clutch becomes contaminated by oil migrating along the rear section of the engine block. However, not every oil leak beneath the engine block originates from the oil sump gasket. Crankshaft seals, oil filter housings, oil cooler modules, turbo lines and cylinder head gaskets can also allow oil to run into the same area.

First clean the engine block, oil sump and surrounding parts using a suitable degreaser. Then inspect the entire flange with an inspection lamp or UV leak detection agent while the engine is warm and idling. Check the oil level according to the vehicle specification and inspect for damaged sump bolts, distorted flanges and impact damage caused by obstacles. If in doubt, measure the flatness of the sump flange using a straightedge and feeler gauge; local deformation often leads to recurring leaks, even with a new gasket. Also check whether the crankcase ventilation system is functioning correctly: excessive crankcase pressure can force an otherwise sound seal outward.

When replacing the gasket, all old gasket material and liquid sealant residue must be completely removed without damaging the aluminium or steel sealing surface. Thoroughly degrease the contact surfaces and inspect the sump for cracks around bolt holes, corrosion and dents. Use only the specified sealant where required by the engine design; an excessively wide bead of sealant can enter the sump and partially block the oil pickup strainer.

Install the oil sump gasket dry or with the specified fitting compound, position the sump without stress and tighten the fastening bolts in the correct sequence to the specified torque. Overtightening distorts thin steel sumps and squeezes out rubber sealing lips, while insufficient clamping force causes oil seepage. Then refill with engine oil of the correct specification, start the engine, check the oil pressure and inspect again for leaks. Based on the chassis number, Braem can help identify the correct gaskets, sealants and associated fastening materials.