Dodge Diplomat 1982-1989 Engine Coolant Thermostat Guide
Keep your Diplomat's engine from overheating or running too cold by choosing the right replacement thermostat.
- A thermostat fails either stuck open (engine runs cold) or stuck closed (engine overheats). Overheating is an emergency; shut the engine off immediately.
- For a stock Diplomat, a standard 195°F thermostat from Gates or Motorad is a reliable, cost-effective choice. A 180°F unit is a common alternative for warmer climates.
- Replacement is a very simple DIY job that can be done in under an hour with basic tools, saving you $100+ in labor costs.
- Always replace the thermostat gasket at the same time to prevent leaks. Most thermostats include one.
Signs of a Failing Thermostat
A thermostat is a wear item that typically fails in one of two ways: stuck open or stuck closed. The symptoms are distinct and tell you what action to take.
Thermostat Stuck Open
This is the less severe failure but still requires attention. A stuck-open thermostat allows coolant to circulate constantly, preventing the engine from getting fully warm. Symptoms include:
- Engine Takes Forever to Warm Up: The temperature gauge on your dashboard may stay in the cold range for a long time after starting the car.
- Poor Heater Performance: The air from your heater vents will be lukewarm or cold because the engine coolant isn't getting hot enough to heat the cabin.
- Decreased Fuel Economy: An engine that runs too cool is inefficient and will use more gasoline.
Thermostat Stuck Closed
A stuck-closed thermostat is a serious problem because it traps coolant in the engine, preventing it from reaching the radiator. This causes the engine to overheat very quickly. Signs include:
- Rapid Overheating: The temperature gauge will shoot up into the red "H" zone shortly after starting the engine.
- Steam from Under the Hood: As the trapped coolant boils, it will create steam that escapes from the engine bay.
- Coolant Leaks or Gurgling Noises: The extreme pressure from overheating can force coolant out of the radiator cap or hoses, and you may hear the coolant boiling.
Choosing the Right Aftermarket Thermostat
For a vehicle like the 1982-1989 Dodge Diplomat, finding a new OEM Mopar thermostat is highly unlikely. Aftermarket brands offer excellent, readily available options that meet or exceed original specifications.
Standard Replacement Brands (Good)
Gates, Motorad: These brands are the workhorses of the aftermarket. They produce reliable, standard-replacement thermostats that are built to original specifications. For a stock Diplomat used for daily driving, a thermostat from Gates or Motorad is a dependable and affordable choice. It's common for different brands to source their parts from the same manufacturer, so you may find a Motorad-stamped thermostat in a Gates box.
Performance Brands (Better/Specific Use)
Edelbrock, Mr. Gasket: These brands are known for performance applications. They often offer "high-flow" or lower-temperature thermostats (like 180°F). A high-flow thermostat isn't necessary for a stock Diplomat engine. While some owners prefer a 180°F thermostat for warmer climates, be aware that Mr. Gasket thermostats have mixed reviews regarding longevity. Edelbrock is a well-regarded performance brand.
Cost of Replacing a Dodge Diplomat Thermostat
| Item | Estimated Cost |
|---|---|
| Aftermarket Thermostat & Gasket | $8 - $58 |
| Shop Labor | $90 - $150 |
| DIY Savings (Total) | $90 - $150 |
Frequently Asked Questions (FAQ)
What temperature thermostat is best for my Diplomat?
For a stock 1982-1989 Dodge Diplomat, a 195°F thermostat is the original factory-specified temperature and is best for overall efficiency. However, many owners of classic cars prefer a 180°F thermostat, which can be a good alternative, especially in hot climates. Avoid thermostats rated below 180°F for a street-driven car, as this can cause the engine to run too cool, increasing wear and reducing efficiency.
Is replacing the thermostat a difficult job?
No, this is an excellent DIY job for a beginner. The thermostat is located in a housing where the upper radiator hose connects to the engine. The job involves partially draining the coolant, removing two bolts, swapping the thermostat and gasket, and refilling the coolant. It typically takes less than an hour with basic hand tools.
Do I need to replace the gasket too?
Yes, absolutely. Never reuse an old thermostat gasket. A new gasket is cheap and essential for preventing coolant leaks. Most new thermostats come with a matching gasket in the box.
Are there any recalls for the Dodge Diplomat thermostat?
No. Searches of the National Highway Traffic Safety Administration (NHTSA) database show no recalls or technical service bulletins (TSBs) for the engine coolant thermostat on the 1982-1989 Dodge Diplomat.
Technical Specifications
The most important specification is the temperature rating, typically 195°F for stock applications or 180°F for a lower-temperature alternative. Ensure the part is specified for the Chrysler 318 V8 or Slant-6 engine, depending on your vehicle's configuration.
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.
- Dodge Diplomat: