Oil Cooler

Many engines have a small oil-to-coolant heat exchanger next to the oil filter. High-performance cars may have separate oil-to-air coolers at the front. Automatic gearboxes often have their own cooler. Engines that tow or run hot for long periods benefit most; the cooler keeps oil from thinning too much.

Hot oil flows through plates or tubes that pass heat to coolant or air.

A leaking oil cooler can mix oil and coolant, which looks like a head gasket fault. Check the cooler seals when you see oil in the coolant.