The oil cooler on the ford 6.0 powerestroke diesel has oil and coolant flowing through it. Coolant is very important, if the coolant isn't maintained and changed regularly it will break down and get trapped in the oil cooler. When this happens the coolant flow is restricted which in turn doesn't allow it to cool the oil costing about $1300 to replace. Replacing the oil cooler is a part of the bulletproof package repair.
Signs that this could be a problem are:
- Coolant loss through the degas bottle
- Fan running at high RPMs