Actually, the coolant outlet housing is covered by powertrain warranty (assuming you haven't gone over 100,000 miles). However, the oil cooler is not. It's just the way the warranty is written.
"Engine coverage includes all internally lubricated parts, engine oil cooling hoses, and lines. Also included are all actuators and electrical components internal to the engine (e.g., Active Fuel Management valve, lifter and oil manifold) cylinder head, block, timing gears, timing chain, timing cover, oil pump/oil pump housing, OHC carriers, valve covers, oil pan, seals, gaskets, manifolds, flywheel, water pump, harmonic balancer, engine mount, turbocharger, and supercharger. Timing belts are covered until the first scheduled maintenance interval. Exclusions: Excluded from the powertrain coverage are sensors, wiring, connectors, engine radiator, coolant hoses, coolant, and heater core. Coverage on the engine cooling system begins at the inlet to the water pump and ends with the thermostat housing and/or outlet that attaches to the return hose. Also excluded is the starter motor, entire pressurized fuel system (in-tank fuel pump, pressure lines, fuel rail(s), regulator, injectors, and return line), as well as the Engine/ Powertrain Control Module and/or module programming."
Notice it doesn't list the oil cooler itself.
"Engine coverage includes all internally lubricated parts, engine oil cooling hoses, and lines. Also included are all actuators and electrical components internal to the engine (e.g., Active Fuel Management valve, lifter and oil manifold) cylinder head, block, timing gears, timing chain, timing cover, oil pump/oil pump housing, OHC carriers, valve covers, oil pan, seals, gaskets, manifolds, flywheel, water pump, harmonic balancer, engine mount, turbocharger, and supercharger. Timing belts are covered until the first scheduled maintenance interval. Exclusions: Excluded from the powertrain coverage are sensors, wiring, connectors, engine radiator, coolant hoses, coolant, and heater core. Coverage on the engine cooling system begins at the inlet to the water pump and ends with the thermostat housing and/or outlet that attaches to the return hose. Also excluded is the starter motor, entire pressurized fuel system (in-tank fuel pump, pressure lines, fuel rail(s), regulator, injectors, and return line), as well as the Engine/ Powertrain Control Module and/or module programming."
Notice it doesn't list the oil cooler itself.
