cooler and flow regulator just described. Oil from the coolers is  routed through two tubes (D) to a Y-fitting, where the floating  control thermostat (A) samples oil temperature and positions  the two oil cooler air-exit doors through the use of a two-door  actuating mechanism. From the Y-fitting, the lubricating oil is  returned to the tank where it completes its circuit. oil cooler air-exit flap. Newer systems use electronic control  systems, but the function or the overall operation is basically  the same regarding control of the oil temperature through  control of the air flow through the cooler. In some lubrication systems, dual oil coolers are used. If the  typical oil system previously described is adapted to two oil  coolers, the system is modified to include a flow divider, two  identical coolers and flow regulators, dual air-exit doors, a  two-door actuating mechanism, and a Y-fitting.  [Figure 6-14] Oil is returned from the engine through a single tube to the  flow divider (E), where the return oil flow is divided equally  into two tubes (C), one for each cooler. The coolers and  regulators have the same construction and operations as the  The following lubrication system is typical of those on small,  single-engine aircraft. The oil system and components are  those used to lubricate a 225 horsepower (hp) six-cylinder,  horizontally opposed, air-cooled engine. In a typical dry sump  pressure-lubrication system, a mechanical pump supplies  oil under pressure to the bearings throughout the engine.  [Figure 6-4]  The oil flows into the inlet or suction side of  the oil pump through a suction screen and a line connected to  the external tank at a point higher than the bottom of the oil  sump. This prevents sediment that falls into the sump from  being drawn into the pump. The tank outlet is higher than  the pump inlet, so gravity can assist the flow into the pump.  The engine-driven, positive-displacement, gear-type pump  forces the oil into the full flow filter.  [Figure 6-6]  The oil  either passes through the filter under normal conditions or,  if the filter were to become clogged, the filter bypass valve  would open as mentioned earlier. In the bypass position, the  oil would not be filtered. As seen in  Figure 6-6 , the regulating  (relief) valve senses when system pressure is reached and  opens enough to bypass oil to the inlet side of the oil pump.  Then, the oil flows into a manifold that distributes the oil  through drilled passages to the crankshaft bearings and other  bearings throughout the engine. Oil flows from the main  bearings through holes drilled in the crankshaft to the lower  connecting rod bearings.  [Figure 6-15] 6-12 Figure 6-14.  Dual oil cooler system. Figure 6-13.  Floating control thermostat.  Dry Sump Lubrication System Operation A B C D E G C F Shaft A Bimetal element B Grounded center contact arm C Electric motor D Gear train E Cam F Floating contact arm G Top view Side view A B E D C Floating control thermostat A Y-fitting B Outlet from cooler tubes D Flow divider E Inlet to cooler tubes C