On most cars you need not remove the engine to get at the sump . But often you have to raise it slightly and wedge it on its mountings so that the sump moves clear of the front- suspension cross member.
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Rotary shaft or oil seals are placed between moving and stationary pieces of machinery to ensure that contaminants, moisture, corrosive materials and abrasives do not damage the various components. They can also prevent unwanted mixing of fluids, including water and oil combining within a machine.