Mileage when the problem started
Owner reports
Selected complaints filed with NHTSA by 2018 Mazda Mazda6 owners, lightly cleaned up (personal details are redacted by NHTSA).
The contact owns a 2018 Mazda 6. The contact stated that while merging onto a freeway the vehicle did not accelerate while pressing the accelerator pedal, lost automotive power. After turning the engine off and back on the vehicle operated as normal but later while driving approximately 65 MPH the failure had reoccurred while attempting the pass a semi-truck on the freeway. The check engine warning light had also illuminated and the vehicle was eventually towed to the local dealer who was unable to determine the cause of the failure. The vehicle was not yet repaired. The manufacturer was not yet contacted. The failure mileage was 67,000.
Took care for routine maintenance to car dealer (Ourisman Mazda Rockville MD). No problems with car. They reported that I had an 'Coolant Leak at the Cylinder Head'. Cost to fix: $6412.47 They reported that it was 'normal wear and tear'. I found a service bulletin from Mazda whereby they admit a manufacturing defect that affected 2.5T engines. They corrected on March 25th, 2021. However, engines prior to this date had this defect. No recalls were created. No warning to owners. My car was within the mileage warranty when they identified the defect (<60k miles and < 5 yrs old). While my car is less than 5 years old, they now identified the leak, but it has over 60k miles. The local dealer said I was out of warranty and there is nothing they could do. …
At less than 95,000 miles, the car suddenly started overheating. Coolant level was fine, maybe ever so slightly low (could still see the coolant in tubing and some in reservoir, which was closer to low than full). Replaced ECT sensor, thermostat and water pump which seemed to fix the issue. Drove for 9-10 days with no issues and it started overheating again. I was able to park quickly afterward at work (<10 seconds). Schedule for drop off at dealer (if car didn't show signs of overheating first (would have called tow truck). Checked fluid levels in car (was ~1Qt low) and topped it off. Drove to dealer (~30min ride) with no issues whatsoever. When dealer looked at it, they said cylinder was warped and leaking, requiring new engine. A just paid off car, with less than 100k miles on it, now needs a new engine that will cost more than half of what it's worth.
Mazda has a huge issue with there HLAs hydraulic lash adjusters. I've driven the car for 60k+ miles and it's ticked every since I got the car. And many people in the community also have the issue. And Mazda says it's fine and to rev the car above 3k rpms. This issue needs to be resolved. Before my warranty went up they said they'd fix it at the dealer if it would tick while in there possession. That's just not reasonable the tick happened as random as it gets. Please please for the sake of Mazda and all it's owners make Mazda fix this as a recall. Many people in the US would be the happiest people in the planet not having to hear there 20k$ car tick like a broken old piece of junk. Thank you for listening. Your truly a franticly hopeless hard working america with a half broken car.
The car only has 70k miles on it. The engine started smoking under the hood. Immediately stopped to look. There was oil leaking but I could not see from where. I took it across the street to the Toyota dealership and had them look at it. They explained to me that there was a crack in the cylinder head and oil was leaking everywhere. Potentially causing a fire or even an explosion. The old was leaking all over the exhaust manifold and engine. I had my 2 toddlers in the car not long before this happened. This is extremely unacceptable. Currently Mazda is saying it will be 7200 to replace the engine and that cost is on me. I think that is absolutely absurd being there are only 70k miles on the car and I bought it brand new. I also kept up with all of the required maintenance.
Bought used with 47k miles. Two weeks later, took it to my mechanic for an inspection, they found a massive oil leak on the back of the motor. Took it back to the dealership and they diagnosed it as a cracked cylinder head, for which there is a known TSB and warranty extension. Unfortunately, the warranty extension only covers a coolant leak from the cracked cylinder head, not an oil leak. Thankfully, the dealership took care of me but had they not, I was looking at a $7k+ repair on a car I had owned for 2 weeks. In the TSB, Mazda acknowledges that there were both design and manufacturing flaws for the affected model years. In acknowledging the issue, they should have issued a recall for affected vehicles, not a simple warranty extension
I took my car in for scheduled maintenance and the technicians at the Mazda dealer found out the tensioner and belt needed to be replaced, when the car is less than 36k in miles. Vehicles being repaired under warranty but a tensioner should not be going out this early in the lifespan of a 2 year old car. I have found a lot of people are complaining for the same issue. This can cause the cars to not run as there's no notice ahead of time that the belt and tensioner are bad. I do have paper work stating tensioner problems. Vehicles should be recalled due to poor manufacturing and parts making it unsafe on the road.
My cylinder head is leaking coolant. There is a well known and well documented issue with these cylinder heads cracking due to poor casting. This has become such a big issue that Mazda has even recalled the cylinder heads, BUT, only if the engine is equipped with Turbo. However, this issue is becoming enormous even for non turbo owners and is a huge safety issue as it can lead to overheating, stalling, and further damage to other components. I feel very strongly that it is time for Mazda to take some responsibility and extend the cylinder head recall to the non turbo engines.
Start engine when cold and it knocks/ taps from the valve cover very loud, found a tab for valve lifters. Mazda said I'm out of warranty and it would be a 2k fix on a car I just bought second hand. A lot of other drivers have experienced the same issue and have even said it's a safety issues as when it happens for long enough it could cause the cams to wear down causing the car to stall out in traffic or in a dangerous road situation. Very dangerous imo and should be fixed for free as Mazda admitted that it's a design flaw of the HLA
Cracked Cylinder Head. At 50,400 miles. This is far too common of a problem for such a new car with so few miles. I have seen many similar reports online. My mechanic was baffled. This is a $5k cost AT LEAST. Mazda has a history of not covering these defects. And it IS a defect, not a simple wear and tear issue. A cracked cylinder head can eventually lead to engine failure, so it is dangerous to drive with it. The problem HAS been confirmed by an independent service center. I got a oil pressure warning sign.
Engine complaints in other Mazda6 years
Frequently asked questions
How common are engine problems on the 2018 Mazda Mazda6?
NHTSA has 32 complaints about the engine & cooling of the 2018 Mazda Mazda6, 55% of the model year's 58 complaints.
Is there a recall for 2018 Mazda Mazda6 engine problems?
No. NHTSA lists no engine & cooling recall for the 2018 Mazda Mazda6, though it has 2 recalls for other components. If the problem is widespread, a repair may still be covered by an extended warranty or a manufacturer service bulletin — ask a dealer.
At what mileage do 2018 Mazda Mazda6 engine problems start?
Half of the complaints with a recorded mileage happened before about 7,000 miles, and 67% before 25,000 miles.
Is it dangerous?
Owners linked 0 crashes, 1 fire and 0 injuries to engine & cooling problems on this model year. If you notice symptoms, have the car checked before driving further.
Source: U.S. National Highway Traffic Safety Administration (NHTSA) — owner complaints through October 20, 2026, recalls and defect investigations; fuel economy from the EPA. Complaints are unverified reports and are not proof of a defect. How we rate model years.