Failure mode - Ford 6.0L Power Stroke

Cooling system degradation / no coolant filtration

Reliability tier: aggregated - verify before ordering, see /disclosure/

Symptoms

brown, cloudy or rusty coolant
sediment / sludge in the bottom of the degas bottle
recurring oil cooler and EGR cooler failures on an otherwise sound engine
gradual overheating tendency under load

Root cause

The factory Motorcraft gold HOAT coolant carries a relatively high silicate load. Under the heat of the EGR cooler the silicates drop out of suspension as a jell-like sludge; residual casting sand from the block adds to it. The 6.0 has no coolant filter from the factory, so this debris circulates and clogs the narrow passages of the engine oil cooler, which then starves the EGR cooler of flow. Independent technical sources call the factory gold coolant a 'probable cause' of the oil-cooler / EGR-cooler failures; it is the widely-accepted upstream trigger of the 6.0 cooling cascade.

Diagnosis

inspect coolant colour and clarity; inspect the bottom of the degas bottle for sediment
test coolant condition / pH / freeze point
if the oil cooler or EGR cooler have failed, assume the coolant is contaminated

Fixes

full cooling system flush, repeated until clean (a silicate-removing flush product is often used) ()

install a bypass coolant filter kit and service it on a schedule (keep gold coolant + add filtration) - cheap and reversible, but a bypass filter only sees roughly 10 percent of coolant flow, so it mitigates rather than fully prevents silicate dropout

6.0L Power Stroke Coolant Filtration Kit (spin-on)

flush and refill with a low-silicate / silicate-free coolant to Ford spec instead of the factory gold (change the coolant chemistry) - removes the silicate source, but is a bigger service job and moves off the exact factory fill

Ford Specification Gold HOAT Coolant (6.0L Power Stroke)

Prevalence

near-universal