Engine Coolant Thermostat Guide for the 1979-1981 Dodge St. Regis
Keep your St. Regis's engine temperature in check with the right aftermarket thermostat.
- A thermostat fails either stuck open (engine runs too cold) or stuck closed (engine overheats).
- For a stock St. Regis, a 180°F or 195°F thermostat is the correct choice.
- Always replace the thermostat gasket and consider testing the new part in water before installation.
- Standard replacement brands like Gates and Motorad are reliable choices for a daily driver.
Is your Dodge St. Regis running too hot or too cold?
The engine coolant thermostat is a common failure point that can cause significant problems. Because it's a simple mechanical part, it can fail in one of two ways: stuck open or stuck closed. A thermostat stuck closed will cause the engine to overheat quickly, as hot coolant can't get to the radiator. A thermostat stuck open will prevent the engine from reaching its proper operating temperature, leading to poor performance, bad fuel mileage, and no heat in the cabin.
Choosing the Right Aftermarket Thermostat
For a classic vehicle like the St. Regis, OEM parts are often unavailable. The aftermarket offers a wide selection of thermostats, but quality can vary. Here’s a breakdown of the brands available:
- Performance Brands (Edelbrock, Mr. Gasket, Mishimoto): These brands often offer "high-flow" thermostats designed for better cooling under heavy use. Edelbrock and Mr. Gasket are well-known in the classic Mopar community. However, some users report reliability issues with certain high-flow designs, so it's important to choose a reputable model. Mishimoto is a strong performance brand, though less traditionally associated with classic Mopars.
- Standard Replacement Brands (Gates, Motorad, Calorstat): These brands aim to meet or exceed original factory specifications. Gates and Motorad are common, reliable choices for daily drivers. It's worth noting that many brands, including Gates, sometimes re-box thermostats manufactured by Motorad. This is a common industry practice and Motorad is generally considered a quality manufacturer.
Always Test Before Installing
Regardless of the brand you choose, it's a wise practice to test the new thermostat before installation. Simply place it in a pot of water on the stove with a thermometer. Watch to see that it opens near its rated temperature before the water boils. This simple step can save you from having to do the job twice.
Known Issues, TSBs, or Recalls
There are no specific recalls or Technical Service Bulletins (TSBs) from the NHTSA related to the engine coolant thermostat for the 1979-1981 Dodge St. Regis. Any cooling system issues on a vehicle of this age are typically due to the age and wear of individual components like the thermostat, water pump, or radiator hoses.
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Thermostat | $7.33 - $56.13 |
| Thermostat Gasket | $2 - $10 |
| Shop Labor | $100 - $180 |
Frequently Asked Questions (FAQ)
What temperature thermostat should I use?
For most stock 318 or 360 V8 engines, a 180°F or 195°F thermostat is recommended. The factory specification was often 195°F for better emissions and efficiency. Some owners in hotter climates or with modified engines prefer a 180°F thermostat for an extra margin of cooling. A 160°F thermostat is generally too cold for a stock street-driven engine and can lead to increased engine wear and poor performance.
Do I need to replace the gasket?
Yes, absolutely. Never reuse an old thermostat gasket. Always install a new gasket with the new thermostat to prevent coolant leaks. It's also a good idea to apply a thin layer of gasket sealant specifically designed for cooling systems.
Can I replace the thermostat myself?
Yes, this is a very DIY-friendly job for most owners. The thermostat is typically located at the front of the engine where the upper radiator hose connects to the engine block. The process involves draining some coolant, unbolting the thermostat housing, swapping the part and gasket, and refilling the coolant. The entire job usually takes less than an hour.
What are the signs of a bad thermostat?
The most common signs are engine overheating (gauge in the red), or the engine taking a very long time to warm up (gauge stays on cold). You might also notice your cabin heater isn't blowing hot air, or the temperature gauge needle moves erratically.
Technical Specifications
Common temperature ratings are 180°F and 195°F. The correct thermostat diameter for most Mopar small block engines (318, 360 V8) is typically 2.125 inches. Always verify the flange diameter if possible before ordering.
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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.