Mazda Coolant Leak Lawsuit Says Defect Can Cause Engine Overheating, Failure

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A proposed class action lawsuit alleges several Mazda vehicle models equipped with SKYACTIV-G 2.5T engines contain a defect that can cause engine coolant to leak, posing the risk of engine overheating, stalling and/or catastrophic engine failure. 

Have you experienced a coolant leak with your 2019-2020 Mazda CX-5, 2016-2020 Mazda CX-9 or 2018-2020 Mazda6? Let us know here. 

The 72-page lawsuit claims 2019-2020 Mazda CX-5, 2016-2020 Mazda CX-9, and 2018-2020 Mazda6 vehicles (class vehicles) suffer from a “latent manufacturing and/or design defect” that can cause “significant structural weakness” in the cylinder head around the car’s exhaust manifold.  

The suit accuses Mazda Motor America and Mazda Motor Corporation of long knowing about the coolant leak defect and actively concealing the problem from drivers. 

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“Despite their longstanding knowledge, Defendants have been unable or unwilling to adequately repair the Class Vehicles for free when the Defect manifests,” the case alleges. 

The alleged defect may allow coolant into an engine’s combustion chamber, where it can mix with engine oil and reduce the oil’s viscosity, hampering lubrication and increasing the chances of premature engine failure, the filing says. Once this occurs, internal engine damage cannot be repaired, and an engine replacement is required, the suit states. 

The Mazda vehicles at issue, like many vehicles, utilize a liquid engine cooling system to dissipate heat generated by the engine’s combustion cycle while in operation, the lawsuit explains. This cooling system incorporates a thermostat module that monitors the engine’s operating temperature by measuring the coolant’s temperature, and when the thermostat reads an optimal engine temperature, it will open and allow coolant to flow between the radiator and engine in order to stay within the ideal temperature range, the filing relays. 

Conversely, when an engine is running cold, the suit says, the thermostat closes and keeps engine coolant from passing between the radiator and the engine, allowing the latter to build heat to reach optimal operating temperature. 

In the Mazda class vehicles, the engine cylinder head is a critical part of the engine’s combustion cycle, as it’s tasked with closing the top of the combustion chamber, the complaint relays. Crucially, the cylinder head, which is bolted to the top of the engine block, also contains coolant passages through which flow significant amounts of engine coolant, so as to transfer heat generated through the combustion cycle away from the engine to prevent overheating, the suit says. 

“The engine cylinder head houses the spark plugs, intake and exhaust runners, valves, oiling passages, and cooling passages. It also has rockers to open and close the valves, and valve springs that hold the camshafts. The function of the cylinder head is to allow the engine to breathe the air it needs for combustion and expel the exhaust gasses.” 

According to the complaint, the first technical service bulletin (TSB) from Mazda regarding potential engine coolant leakage stemming from the cylinder head came in October 2021, and subsequent bulletins to dealers noted that “there may be cracks at the stud bolt hole or outside of the exhaust manifold flange on the cylinder head.” 

“According to Defendants’ TSB, these cracks may be caused by ‘[e]xpansion characteristics of the exhaust manifold during usage causing unexpected force to certain areas of the cylinder head. Residual stress generated during production in the cylinder head material may be greater than expected. The external force from the exhaust system when driving over bumps may cause unexpected force to certain areas of the cylinder head. To eliminate this concern, the design of the exhaust manifold gasket and the cylinder head has been modified to reduce the force on the cylinder head.’” 

Repair methods for the Mazda engine coolant leak defect range from replacing an engine’s cylinder head assembly to total engine replacement, for which proposed class members are left to pay out of pocket, the lawsuit says.

Rather than fix the alleged defect, Mazda has told drivers who bring their cars to authorized dealers that the engine coolant problem is not covered under warranty, the filing claims. 

The lawsuit looks to cover all persons in the United States who bought or leased a 2019-2020 Mazda CX-5, 2016-2020 Mazda CX-9 or 2018-2020 Mazda6. 

Have you experienced a coolant leak with your 2019-2020 Mazda CX-5, 2016-2020 Mazda CX-9 or 2018-2020 Mazda6? Let us know here.