P0128 on Ford: How to Diagnose & Fix

The 1.5L EcoBoost in 2014-2019 Ford Fusion is affected by the same open-deck cylinder block design defect as the Escape. Coolant leaks internally from the block passages into the combustion chambers due to insufficient sealing surface and porous block material that cannot maintain coolant pressure over time. Ford TSBs 19-2139, 19-2375 and 20-2100 direct short block and head gasket replacement on 2014-2019 Fusion 1.5L vehicles, and Ford Customer Satisfaction Program 21N12 provides extended coverage for the short block replacement on certain 2017-2019 Fusion 1.5L vehicles. A consolidated class action lawsuit covers 2013-2019 Fusion and Escape with 1.5L, 1.6L, and 2.0L EcoBoost engines. Some owners have experienced engine failure with no warning - no check engine light before coolant hydrolocked the cylinder.

The 2.0L EcoBoost in 2017-2019 Ford Escape suffers from the same fundamental open-deck block design defect as the 1.5L variant. Coolant leaks internally through the cylinder head/block interface into the combustion chambers. Ford issued TSB 19-2208 in 2019 (superseded by TSB 19-2346 in December 2019) acknowledging the problem. The fix per TSB requires complete long block engine replacement, which can cost up to about $9,500 at dealers. The TSB covers only Escapes built on or before May 16, 2019, so 2020+ 2.0L engines are not covered by this bulletin. Class action lawsuits are pending covering 2013-2019 EcoBoost vehicles.

The 2.0L EcoBoost engine in 2015-2018 Ford Edge is notorious for internal coolant leaks where antifreeze bypasses the head gasket and floods the combustion chambers. Ford's open-deck block design with scored channels between cylinders creates an inadequate sealing surface that degrades over time. Ford acknowledged this in TSB 19-2208 (superseded by TSB 19-2346, later TSB 22-2229) and the prescribed fix is complete engine long block replacement costing $7,500-$10,500. Ford never issued a recall, relying instead on TSBs and limited extended warranty coverage. 2019 and later Edges are not included in these coolant-intrusion TSBs. CarComplaints.com lists 43+ complaints for the 2017 Edge alone specifically for coolant leak into cylinder.

On the 3.5L and 3.7L Duratec V6 the water pump is driven off the timing chain and lives INSIDE the oil-lubricated front timing cover, not bolted to the outside of the block. When the pump's shaft seal and bearing wear out (commonly 90k-130k miles), coolant does not drip onto the driveway - it runs down the weep passage and, once the passage plugs or the seal fully lets go, straight into the crankcase. Owners report the first sign is a slowly dropping coolant reservoir with no visible external leak, then milky residue on the dipstick and oil cap. Coolant-contaminated oil destroys rod and main bearings and scores cylinder walls, which is why so many of these turn into engine replacements rather than pump jobs. A class-action suit was filed against Ford over this design. The labor is brutal because the front cover, timing chains and often the engine's front accessory drive must come off, and many shops quote the job with the engine partially lifted.

The 1.6L EcoBoost engine in 2014-2016 Ford Transit Connect has documented issues with coolant loss, overheating, and in severe cases engine fires. Ford issued Recall 17S09 (NHTSA 17V209) covering 2013-2015 Transit Connect models with the 1.6L GTDI engine (2016 models are not included in this recall): if driven with an insufficient coolant level, the cylinder head may overheat, crack and leak oil, which can lead to an engine compartment fire. The 1.6L EcoBoost was also susceptible to head gasket failure and internal coolant leaks similar to the 1.5L and 2.0L EcoBoost engines in other Ford models. The engine was dropped after the 2016 model year. The FordTransitConnectForum documents numerous cases of premature engine failure on 1.6L-equipped vans used in commercial service.

Early 2.3L EcoBoost Mustangs can experience coolant intrusion into the combustion chamber through cracked cylinder head or head gasket failure. This can cause white smoke from exhaust, coolant loss, and potential engine damage if not addressed.

The 1.0L EcoBoost uses a brittle nylon degas/coolant return hose running from the top of the expansion tank to the engine. Over thousands of heat cycles the nylon becomes brittle and cracks or snaps, often at highway speed. Because the engine has a very small coolant capacity and high thermal load, a burst hose causes total coolant loss in seconds; the aluminum cylinder head then overheats almost instantly, warps, and blows the head gasket — the failure mode owners nickname 'EcoBoom.' In March 2015 Ford issued a UK Field Service Action to replace the coolant pipe on about 44,682 1.0L cars built between October 2011 and October 2013, and in 2018 Ford UK agreed to pay 100% of dealer repair costs for 1.0L overheating failures linked to the fault. Owners are advised to check whether the hose from the expansion tank is hard black plastic (original, at-risk) or flexible rubber (updated).

The 6.0L Powerstroke diesel (2003-2005 Excursion) is notorious for TTY head bolt stretching under boost pressure, causing head gasket failure. This is the same engine used in Super Duty trucks and is one of the most problematic diesel engines Ford produced.

F-150s with an automatic transmission route ATF through a cooler built into the radiator end tank. When the internal barrier cracks or corrodes, the two fluids cross-contaminate: pink/foamy 'strawberry milkshake' ATF appears in the coolant and coolant gets into the transmission. Coolant is highly destructive to transmission clutches and can cause total transmission failure if driven on. The radiator can fail internally with no external leak, so owners often discover it only after shift problems or a milkshake in the overflow bottle.

EcoSport owners report thermostats sticking open, leaving the engine running below its target operating temperature. The signature is a P0128 'coolant thermostat below regulating temperature' code together with weak cabin heat and worse fuel economy, because the ECU holds a richer warm-up strategy while the engine never reaches closed-loop temperature. What makes this awkward on the EcoSport is that owners on the 2018+ forum have found the vehicle carries TWO thermostats, so replacing the obvious one and reusing the other leaves the code coming back — and several owners report P0128 persisting through repeat coolant temperature sensor replacements because the sensor was never the fault. Coolant seepage from the plastic thermostat housing and its gasket is the closely related failure, showing up as slow, unexplained coolant level loss rather than a puddle. Both engines are affected; on the 1.0L the consequences are much worse because of its small coolant volume, so treat any coolant loss on a three-cylinder car as urgent.

The 2003-2007 6.0L Power Stroke in the F-350 uses torque-to-yield head bolts in a high-cylinder-pressure engine with relatively few fasteners per cylinder. Under repeated heat cycles, and especially with the elevated cylinder pressures that come from towing at weight or from any power tuning, the TTY bolts stretch and lose clamp load. The head lifts momentarily, the gasket fire ring loses its seal, and combustion gas is pushed into the cooling system. This is the failure that gave the 6.0L its reputation. It is frequently downstream of the plugged oil cooler / EGR cooler problem, because the resulting overheating is what finally pushes the bolts past yield. F-350 dually and chassis-cab trucks working near GVWR see it earlier than lightly used trucks.

On certain 2022-2023 Maverick hybrids built at Hermosillo from February 3, 2021 through January 13, 2023, Ford Customer Satisfaction Program 24N04 says the printed circuit board inside the exhaust gas heat recovery (EGHR) actuator housing may fail due to water ingress. The EGHR valve can then stick in position and the malfunction indicator lamp comes on with EGHR codes such as P2C22, P2C23 or P237C-P237F. Ford's coolant-leak finding in the same program applies to the F-150 hybrid, not the Maverick.