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 extended warranty coverage to 7 years/84,000 miles for short block replacement per TSB 19-2139 and TSB 19-2375. 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 2.3L EcoBoost engine in 2015-2019 Mustangs is prone to head gasket failure, particularly in vehicles that experience repeated heat cycles or are driven hard. Block distortion over multiple thermal cycles creates gaps between the engine block and cylinder head that the gasket cannot seal, allowing coolant to enter the cylinders when the engine is cold. Ford redesigned the engine for 2020+ models.

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 4.0L SOHC V6 used in 2005-2010 Mustangs commonly develops coolant leaks from the composite thermostat housing and related seals. The plastic housing can warp or crack with age and heat cycling, causing external coolant seepage and sometimes overheating if the leak worsens. This is a well-known issue across Ford applications using the same 4.0L engine and is frequently documented in owner forums and repair databases.

The 3.5L V6 engine (both naturally aspirated and EcoBoost versions) features an internal water pump located under the engine front cover. When this pump fails, it can leak coolant internally into the engine crankcase, contaminating the oil and potentially causing catastrophic engine damage if not caught immediately.

The 2.0L EcoBoost in 2015-2019 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 (later updated to TSB 22-2229 in 2022) acknowledging the problem. The fix per TSB requires complete long block engine replacement costing $7,000-$10,000 at dealers. Ford redesigned the block in 2019 with a closed-deck layout, so 2020+ 2.0L engines are not affected by this specific issue. Class action lawsuits are pending covering 2013-2019 EcoBoost vehicles.

The 2.0L EcoBoost engine in 2015-2019 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 (later TSB 22-2229) and the prescribed fix is complete engine long block replacement costing $7,700-$10,000+. Ford never issued a recall, relying instead on TSBs and limited extended warranty coverage. The 2020+ redesigned closed-deck block resolved this issue. 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 2014-2018 Ford Transit Connect has documented issues with coolant loss, overheating, and in severe cases engine fires. Ford issued Recall 14S11 (NHTSA 14V309) for 2013-2014 models covering coolant leakage from the cylinder head that could contact hot engine components and cause 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 discontinued and replaced by the 2.0L EcoBoost in later Transit Connect models. The FordTransitConnectForum documents numerous cases of premature engine failure on 1.6L-equipped vans used in commercial service.

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.

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 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.' Ford issued safety action 17S09 (and related regional campaigns) to replace the brittle nylon hose with a reinforced rubberized version, and in the UK agreed to fund repairs after a wave of overheating fires. Owners are advised to check whether the hose from the expansion tank is hard black plastic (original, at-risk) or flexible rubber (updated).

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.

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.

The 2.3L Duratec-equipped Ranger is known for coolant leaks from the thermostat housing assembly and related plastic cooling components. Owners report seepage or sudden cracking near the housing, leading to coolant smell, low coolant level, and occasional overheating if ignored. The problem is common enough in owner forums and repair databases to be considered a known age-related weakness on these trucks.