Engine Coolant Thermostat Replacement Guide for the 1975-1982 Chrysler Valiant
Learn how to spot a failing thermostat and choose the right replacement for your classic Valiant.
- A failing thermostat can cause overheating (stuck closed) or a lack of heat (stuck open).
- The correct stock temperature rating for a 1975-1982 Valiant is 180°F.
- Replacement is a simple, beginner-friendly DIY task that takes less than an hour.
- Always replace the thermostat gasket at the same time to ensure a leak-free seal.
Symptoms of a Failing Thermostat
A thermostat is a wear item that can fail in two ways: stuck open or stuck closed. Each failure has distinct symptoms.
Stuck Closed: This is the most serious type of failure. When the thermostat is stuck shut, coolant cannot get to the radiator to be cooled. This will cause the engine to overheat quickly, which can lead to severe engine damage like a blown head gasket or warped cylinder head.
- Temperature gauge quickly rises to HOT.
- Boiling, gurgling, or rumbling sounds from the engine.
- Coolant leaking or boiling out of the overflow tank or from the thermostat housing area.
Stuck Open: This failure is less critical but should still be addressed. A thermostat stuck open allows coolant to circulate constantly, preventing the engine from reaching its proper operating temperature.
- Engine takes a very long time to warm up, or never reaches the middle of the temperature gauge.
- Heater blows lukewarm or cold air, even after the car has been running.
- Noticeably worse fuel economy because the engine is running too cool.
Choosing the Right Aftermarket Thermostat
For a vehicle of this age, new OEM Mopar parts are generally unavailable, making aftermarket the go-to choice. The most important factor is choosing the correct temperature rating. Based on historical service documents, the standard rating for classic Valiant engines is 180°F. Using a thermostat with a different rating can affect performance and engine management. Always replace the gasket when replacing the thermostat to prevent leaks.
Brand Quality Tiers
When shopping for a new thermostat, you'll find several brands available:
- Gates: A well-known and respected manufacturer of cooling system components, often considered an OE-equivalent supplier. A Gates thermostat is a reliable, high-quality choice for a stock replacement.
- Edelbrock: Known for performance parts, an Edelbrock thermostat may be marketed as a "high-flow" option. This can be beneficial for modified engines but is generally not necessary for a stock Valiant.
- Motorad: A widely available aftermarket brand that often serves as a budget-friendly option. While functional, some owner forums report mixed quality and occasional premature failures compared to other brands.
Typical Replacement Costs
Replacing the thermostat on a 1975-1982 Valiant is a simple and inexpensive job. The part itself is very affordable, and labor is minimal.
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Thermostat | $8 - $27 |
| Shop Labor | $75 - $150 |
| Total Professional Replacement | $83 - $177 |
Frequently Asked Questions
Is it hard to replace the thermostat myself?
No, this is a very easy DIY job for a beginner. It typically involves draining a small amount of coolant, removing two bolts on the thermostat housing located at the front of the engine, swapping the old thermostat and gasket for the new ones, and reassembling. The entire process usually takes less than an hour.
Should I use a 180°F or 195°F thermostat?
For a stock 1975-1982 Valiant, a 180°F thermostat is the correct original specification. Using a hotter 195°F thermostat, which became common on later computer-controlled cars for emissions reasons, is not recommended unless you have made specific engine modifications that require it.
Do I need a "fail-safe" thermostat?
Some aftermarket brands offer "fail-safe" thermostats designed to lock in the open position if they fail. While the idea is to prevent a catastrophic overheat, some mechanics report that these designs can be less reliable and may fail in the open position prematurely. A quality standard-design thermostat from a reputable brand is often the most reliable choice.
My temperature gauge needle moves around a lot. Is that the thermostat?
It could be. Erratic temperature readings, where the gauge fluctuates between cool and normal, can be a sign of a thermostat that is sticking or opening and closing incorrectly. However, it can also be caused by air in the cooling system or a faulty temperature sending unit, so further diagnosis may be needed.
Technical Specifications
OEM Part Numbers: 2129205
Standard Temperature: 180°F (82°C)
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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.