Zalvern

TakeshiJin, This thread is old from its last post. But just so you aren't left without a response, I'll try to explain what is most likely the problem: Is your MKZ a 2017 (especially built in 2016)? The "water running behind dash" that is air trapped in the highest point in the coolant system. This happens due to coolant slowly leaking into the cylinder chamber on 2.7L and 3.0L Ecoboost engines. Even some Continentals may have this issue. The final result is the spark plug(s) get contaminated with coolant, causing them to become wet and foul. The first way to catch this problem is to inspect the spark plugs. If one of them is found wet, this is the confirmation needed a faulty cylinder head was installed on the engine at factory assembly. The engine is going to need to get new cylinder heads to perform correctly. Do not accept switching in new spark plugs until the cylinder heads are replaced either, as they will immediately foul out again. As as customer, request that service advisor/tech show you what the spark plugs look like if you're uncomfortable checking them yourself. The wet spark plug is why both MPG and performance is poor, and if you get really aggressive the car at some point, it may throw a CEL misfire code and shudder while driving, only for it to clear up once off the throttle for a bit. I am curious if jcarwright99 solved his issue and discovered needing new cylinder heads installed on his engine. The issue was a lot more widespread than Ford/Lincoln made it seem, as only a few resulted in "blown" engines for units built in 2016 and even some early 2017s. It may be a minor leak on the majority and not harm the engine, but corrupt spark plugs is what hurts performance and MPGs. New Cylinder heads being installed on the engine was the only way all these issues mentioned in this thread (that my own 2017 MKZ 3.0 suffered in the beginning) were solved. Good luck.