I looked at a Ford F-150 truck for sale today with the 5.4L V8 Modular motor. The truck had no running issues.
After raising the hood, I noticed something odd. There is solid material stuck to the inside of the coolant system bottle. I have not seen this before. I have seen extensive mixing of oil and coolant, this usually looks like a brownish sludge.
What causes solid material to accumulate, and in this case stick to the inside of the coolant bottle? Is this indicative of a failure in the cooling system?