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Engine lubrication

The 12v engine's oil supply is provided by a crescent type oil pump driven by the crankshaft. The oil filter and oil cooler are located on the left side of the die cast aluminum oil sump.

The sump is made up of two parts, an upper and lower section. The upper section is bolted to the bottom of the engine and the transmission housing (this helps to stiffen the engine and transmission assembly).

The oil sump is below and away from the crankshaft. This helps to reduce oil foaming.

Baffles are cast in the lower section of the sump. They help ensure that oil remains around the oil pickup tube even during hard turns.

The picture at the left shows the AAH oil sump setup, which differs from the AFC oil sump setup (See the Features section for more details).
Pump   The 12v engine's lubrication system changed somewhat between the AAH and AFC versions. In addition to the new oil sump setup, the oil filter, oil cooler, and oil pump changed.

The changes inside the oil pump were the most significant. In the AAH engine, oil circulation enters from the pressure side (F) via the 16 bar (232 psi) oil pressure relief valve that screws in to the sump assembly. From there, it circulates to the oil filter. Oil also circulates from the pressure side (F) to the pressure relief valve in the oil pump (D) via channel (C).

In the AFC engine, the oil enters the pump via the oil sump, through the oil cooler and filter, then back to the oil pump (G) to recess (H) and, at the same time, to bearing positions via channel (B), and to the integrated pressure relief valve (D) via channel (C). The advantage to this setup is that oil pressure is regulated on the 'clean' side of the oil filter.

The two oil pump versions are not interchangable; the pumps will only fit on the engine that they were designed for.
Oil enters the oil pump (E) via the oil pickup (G).

Oil pressure comes from the oil pump (E) past the upper part of the oil pan to the 11 bar (150 psi) pressure relief valve (H) integrated in the sump assembly (in the AAH engines the valve opens at 16 bar / 232 psi and screws into the sump assembly), the oil pressure switch (F), and the oil filter (A) to the 5 bar (72 psi) pressure relief valve (C) integrated in the sump assembly (AFC only; this valve does not exist on AAH engines). The 5 bar pressure relief valve (C) controls the oil pressure to the AFC engine.

The 11 bar (160 psi) pressure relief valve (H) is a safety valve that opens only at high RPM and cold engine temperatures.

Lubrication system   The oil pump supplies oil to the oil filter and oil cooler, and then the engine block. The oil passages from the pump to the filter and cooler are cast into the upper section of the oil sump.

Oil is supplied to a central galley in the engine block and then to the main bearings. Oil is then supplied to the cylinder heads for the hydraulic lifters and the camshaft bearings.

Oil is supplied to the right cylinder head from the central galley. The left cylinder head is supplied oil from an additional oil passage in the #2 main bearing support.

Check valves are located in the engine block steadying chamber, one for each oil passage to the cylinder head. They are used to prevent oil from draining back out of the hydraulic lifters when the engine is off.

Pressure relief valves, one in each cylinder head, limit the oil pressure to the hydraulic lifters and camshaft bearings to 2.7 bar (39 psi). This limit in pressure prevents the lifters from being pumped up too much.

Each head gasket has a calibrated hole in the oil supply passage. These holes ensure that full oil pressure is maintained in the engine block when the oil pressure relief valves are open.

Lubrication system component locations

  • Oil pressure relief valve: regulates system pressure
  • Oil pressure sending unit: sender for oil pressure gauge (0.3 bar / 4.35 psi)
  • Oil pressure switch: sender for oil pressure warning light (0.9 bar / 13 psi): gray connector
  Component Locations