On this engine the coolant disappears internally, with no external trace. It starts in two places: the material of the plastic degas hose running to the expansion tank ages and cracks, or the connection of the coolant hose to the cylinder head lets through. In a more severe case the degas chamber of the cylinder head itself cracks or warps, and then the coolant seeps into the combustion chamber or into the oil. Because no puddle forms, the level drops quietly and the engine overheats: the temperature gauge starts to climb mainly after a longer motorway stretch. The further signs are white steam from the exhaust, a sweetish smell, and misfiring that gets worse when warm. Ford issued a service bulletin for this (19-2346) and an extended warranty for certain model years as well. The coolant hose and the degas tank are available in a revised design, and engines built around 2016 and later already have the better material connection and tank. If the fault is found early and the head has not warped, the repair is replacing the hose and the tank, between 50 and 300 euro. If it is found late, the head gasket or the whole cylinder head follows, and that is 2,500 to 5,500 euro. The leak is reported above 80,000 km and the cracking of the head above 100,000 km.

In the smaller models, the Fiesta, the Fusion and the B-Max, the IB5 holds up well, but in the larger Focus and especially the Mondeo it does less well: there the engine torque and the weight of the car put a heavier load on the same gearbox.

The timing belt runs in oil, under its cover, and cannot be seen from outside. Contaminants building up in the oil attack the belt material, so it breaks down early if oil changes are skipped or the oil level drops below the minimum on the dipstick. Fragments of the disintegrating belt end up in the sump and can block the oil pickup, after which the engine is left without oil pressure.