Lincoln MKZ Engine Coolant Thermostat Guide for 2007-2020 Models
Understanding why your Lincoln MKZ is overheating, running cold, or has a P0128 code.
- A thermostat stuck open is the most common failure and the primary cause of a P0128 check engine light code.
- For most 2013-2020 models, it is best to replace the entire thermostat housing assembly, not just the thermostat, to prevent future leaks.
- Always match the new thermostat to your MKZ's specific engine (2.0L, 3.0L, 3.5L, 3.7L) and use the OEM-specified temperature rating.
- After replacement, the cooling system must be properly bled to remove air pockets and prevent overheating.
Is Your MKZ's Thermostat Stuck Open or Stuck Closed?
A thermostat typically fails in one of two ways, causing distinct problems for your Lincoln MKZ.
- Stuck Open Failure: This is the more common failure on modern vehicles. The thermostat remains open all the time, constantly circulating coolant to the radiator. Your engine will take a very long time to warm up, or it may never reach the proper operating temperature, especially in cold weather. This leads to poor fuel economy, reduced heater performance, and will almost always trigger a Check Engine Light with code P0128.
- Stuck Closed Failure: This is a more serious problem. The thermostat is stuck closed and will not open to let hot coolant get to the radiator. This will cause the engine to overheat quickly, which can lead to severe engine damage like a warped cylinder head or blown head gasket if not addressed immediately.
Thermostat Only vs. Full Housing Assembly
When shopping for this part, you will see a huge price difference, from under $20 to over $300. This is because there are two types of parts available.
- Thermostat Only: This is just the small, metal valve itself. On some older MKZ models, particularly the first generation (2007-2012) with the 3.5L V6 engine, you may be able to replace just the thermostat.
- Thermostat Housing Assembly: Newer MKZ engines, like the 2.0L and 3.7L, often use a complete plastic housing that includes the thermostat, the coolant temperature sensor, and the outlet pipe. These plastic housings can become brittle over time and develop cracks or leaks. In most cases, replacing the entire assembly is the recommended and more reliable repair. 🎬 Watch this step-by-step guide for replacing the 2.0L thermostat housing.
Choosing the Right Aftermarket Thermostat Brand
With several brands available, choosing the right one can be confusing. Here’s a breakdown of the options for your MKZ.
- Motorcraft: This is the Original Equipment (OEM) brand from Ford. It is the benchmark for quality, fit, and correct temperature rating. If you want a guaranteed direct replacement with no guesswork, Motorcraft is the safest choice.
- Gates: Gates is a major, reputable aftermarket manufacturer of cooling system parts. They are generally considered a high-quality alternative to OEM parts. While one forum user reported a failure, this is not a widespread complaint.
- Motorad: This is a very common aftermarket brand, and they also manufacture thermostats for other brands like Stant. User reviews are mixed; some report premature failures, while others have no issues. They are a budget-friendly option, but may not have the same longevity as OEM.
- Mishimoto: This is a performance-oriented brand. Their thermostats are designed to open at a lower temperature (around 154°F) than the stock thermostat (around 180-190°F). This is intended for highly modified or racing engines. For a daily driven MKZ, using a lower-temperature thermostat is not recommended as it can hurt fuel economy and cause the engine to run too cool.
- Calorstat / Facet: These are standard aftermarket brands. While less discussed in owner forums, they provide an OEM-equivalent option that meets basic replacement needs.
Known Issue: 2.0L EcoBoost Coolant Intrusion
Owners of 2017-2019 Lincoln MKZ models with the 2.0L EcoBoost engine should be aware of a known issue detailed in Ford's Technical Service Bulletin (TSB) 19-2346. This issue involves a potential for coolant to leak into the engine's cylinders due to a specific engine block design. Symptoms can include coolant loss with no visible leak, white exhaust smoke, and engine misfires. This is a serious engine problem, not just a thermostat failure. A class-action lawsuit was also filed regarding this issue.
🎬 See this detailed breakdown of the EcoBoost coolant intrusion problem.Frequently Asked Questions (FAQ)
What is the P0128 code on my Lincoln MKZ?
The P0128 diagnostic code means "Coolant Temperature Below Thermostat Regulating Temperature." This code is set by your car's computer when it detects that the engine is not warming up to its proper operating temperature within a specific amount of time. The most common cause for this code is a thermostat that is stuck in the open position.
Do I need to replace the whole housing or just the thermostat?
For most 2013-2020 MKZ models, the thermostat is integrated into a plastic housing. These housings are a common failure point, prone to cracking and leaking. It is highly recommended to replace the entire assembly to prevent future leaks, even if only the thermostat has failed.
What temperature thermostat should I buy for my MKZ?
You should always use a thermostat with the same temperature rating as the original part specified for your engine. This is typically between 180°F and 195°F. Using a lower temperature thermostat, like a racing one from Mishimoto, can prevent your engine from reaching its optimal temperature, negatively affecting performance and efficiency on a stock vehicle.
Do I need to bleed the cooling system after replacing the thermostat?
Yes, this is a critical step. After replacing the thermostat and refilling the coolant, air gets trapped in the system. You must bleed the cooling system to remove these air pockets. Failure to do so can cause the engine to overheat, even with a new thermostat, because the trapped air prevents coolant from circulating properly.
🎬 Watch how to properly bleed the cooling system on V6 engines.Helpful Videos
Technical Specifications
OEM Part Numbers: 1X4Z-8575-FA 3M4Z-8575-B RT-1233 RT-1221 RT-1253
Temperature ratings vary by engine, typically 180°F, 187°F, 190°F, or 192°F. Many models use an integrated housing assembly which includes the thermostat, seal, and sensor.
We Have This Part in Stock
The information in this article is provided for general reference and educational purposes only. Vehicle specifications, procedures, and part compatibility can vary by production date, trim level, and region. Always consult your vehicle's factory service manual and verify part numbers before purchasing or performing repairs. Safety-critical components such as airbags, seat belts, and braking systems should be installed by a qualified professional.
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