2019 Mazda CX-9

The engine cylinder head developed an internal coolant leak, allowing coolant to enter the combustion chamber. This caused engine overheating and smoke coming from the tailpipe while driving. A dealer performed a coolant pressure test confirming coolant leaking into the combustion chamber, and wet/dry compression testing on all 4 cylinders showed low and inconsistent readings consistent with cylinder head coolant intrusion (Cylinder 1: 105/125 psi, Cylinder 2: 115/125 psi, Cylinder 3: 110/175 psi, Cylinder 4: 160/190 psi). Overheating creates a risk of sudden loss of power and potential engine failure while driving, including on the highway. The problem has been confirmed and diagnosed by an authorized dealer service center, and the manufacturer's technical hotline department reviewed the diagnostic findings directly. Warning symptoms (overheating codes and visible tailpipe smoke) first appeared at the time the vehicle was brought in for diagnosis. The manufacturer has an active technical service bulletin addressing cylinder head coolant leaks on this engine and model, along with a related warranty extension program, but has denied coverage for this repair on the basis that the leak is internal rather than external.

2019 CX-9 GT, 30K miles, in August found coolant leaking under the car. This was 5 months past the warranty (but only 30K miles!). After doing research online, I found this is a massively common issue with all engines from several years encompassing 2019, where the coolant leaks due to a cracked cylinder head. There is a TSB from Mazda, which requires replacement of the engine, once the crack is developed. I immediately called Mazda corporate on 8/15/2024 and opened the case with them. They said they can try to assist, but first I have to take the car to the dealer for diagnosis of the problem. Had to wait 2 weeks, then leave the car, they did a full inspection and confirmed cracked cylinder head. Dealer opened up claim with Mazda (which apparently is separate from the case I made when I called the corporate). I had to go back because Mazda warranty dept. was asking the dealer to prove the engine was overheating, which it hasn't yet, because I kept adding coolant, so the engine never overheated. But the dealer lowered the coolant and had the engine overheat a little bit just to generate the computer code the warranty dept was requiring. This itself was an unnecessary additional potentially damaging scenario, completely unnecessary when the crack in the cylinder head was already found, and the coolant leak is clearly present. After all this, Mazda lowered their original quote from $10K to $6K and expect me to pay this to replace the engine. I called the corporate (customer relations) many times, but they said if the warranty dept. decided this, they cannot change it. And there's no way to talk to warranty dept. directly (not customer facing). We purchased a brand new factory assembled car for well over $40K. Due to a very common, Mazda acknowledged, engine manufacturing defect, the major component of the vehicle, its engine, requires replacement at only 30K miles! This is NOT a reasonable expectancy when purchasing any vehicle.

The engine developed a sudden coolant leak on the rear of the engine. A warning comes up stating that the car could overheat and lose power. After a few minutes and no sign of the car overheating, the car loses power and slows down on its own. The car has not yet been seen by the dealer or a repair shop due to no appointments available. Mazda USA has issued a TSB stating the issue with the engine and they state that a design flaw causes the cylinder head to crack because of the external forces from the exhaust system over bumps. The failure appeared all of a sudden with no warning lights or indications, it just started leaking a small amount of coolant one day. Now I'm waiting for Mazda USA to tell us how they are going to remedy this issue and provide assistance. According to their TSB this affects three different vehicle models with the same 2.5L turbo engine built from 2016 to 2020.