Basically, it is behind the crankshaft pulley on the outside of the engine. To help visualize its' position, locate the oil filter mount. That is part of the oil pump. The timing belt, crank pulley, oil pan, and Power Steering pump must all be removed to gain access. Did you say you were thinking of replacing the timing belt anyway? Go for the water pump and belt tensioner too while you're at it.
None, oil pumps are not prone to wear out or fail. If the oil pump is actually failing the whole engine is probably worn.
The oil pump is behind the front cover driven by the timing belt.
The oil pump is basically the front cover of the engine and is driven by the crankshaft. You WILL need a repair manual for this operation.
Bottom front of engine.
5W-30 is the preferred oil ( according to the 1996 Mercury Villager Owner Guide )
The oil pump assembly is behind the front timing cover and fits around the crankshaft snout. Needless to say, this requires considerable disassembly to get at.
Bolted to the bottom of the engine block INSIDE the oil pan
According to the 1998 Mercury Villager Owner Guide ( 5W-30 ) is the preferred oil
10w30
5W-30
I looked at the Mercury Villager Owner Guides from ( 1996 , 1999 , and 2002 ) With engine oil filter change : Each Owner Guide shows ( 4.2 U.S. quarts )
There is generally no reason to replace an oil pump unless the engine is being rebuilt. Low oil pressure is usually the result of worn internal engine bearings, not a bad oil pump. The oil pump normally produces much more oil pressure than the engine needs.