Engine Coolant Thermostat Guide for the 1978-1980 Dodge RD200
Keep your classic Dodge RD200's engine from overheating or running too cold by choosing the right thermostat.
- A thermostat can fail stuck-closed (causing critical overheating) or stuck-open (causing the engine to run too cool).
- For a stock RD200, use a quality 195°F thermostat for best performance; avoid cheap brands known for poor quality control.
- Replacement is a simple DIY job for most owners, requiring basic tools and about an hour of time.
- No recalls or TSBs are on file for the thermostat on this vehicle; failures are due to age and wear.
Is Your Dodge RD200 Thermostat Failing?
A thermostat is a simple mechanical part, but when it fails, it can cause serious problems. On a truck from the 1978-1980 era, failures are usually due to age, corrosion, or debris in the cooling system. There are two ways a thermostat typically fails:
Thermostat Stuck Closed (Serious)
This is the most dangerous failure. A stuck-closed thermostat traps coolant inside the engine, preventing it from reaching the radiator. This will cause your engine to overheat very quickly, which can lead to severe damage like warped cylinder heads or a cracked block. If you see the temperature gauge shoot into the red, pull over immediately and shut off the engine to prevent catastrophic failure.
Thermostat Stuck Open (Moderate)
If the thermostat is stuck open, coolant flows to the radiator all the time. This makes it very difficult for your engine to reach its proper operating temperature, especially in cooler weather. You will notice the temperature gauge stays low, your heater blows lukewarm air, and your fuel mileage may get worse because the engine is running too rich. While less critical than overheating, this can cause long-term engine wear.
Choosing the Right Aftermarket Thermostat
For a vintage truck like the RD200, new OEM thermostats from Mopar are generally not available. The market consists of aftermarket brands that vary in quality. Here’s a breakdown of your options:
Tier 1: OEM Quality & Performance Brands
- Calorstat: Often an OEM supplier for many European and some domestic brands, Calorstat is generally regarded as a high-quality, reliable choice that you can trust to perform like the original.
- Edelbrock / Mr. Gasket: These are performance brands that offer high-flow thermostats. They are designed for modified engines that may require extra cooling capacity. An Edelbrock or Mr. Gasket thermostat can be a good upgrade if you use your truck for heavy hauling or have a modified engine, but may be unnecessary for a stock daily driver.
Tier 2: Standard Aftermarket (Use with Caution)
- Gates: Gates is a well-known name in cooling systems, but forum discussions show mixed reviews for their thermostats, with some users experiencing temperature swings.
- Stant: This brand was once considered the gold standard for aftermarket thermostats. However, many enthusiasts report a significant drop in quality in recent years, with some parts failing prematurely. Older, new-old-stock (NOS) Stant parts are excellent if you can find them.
Tier 3: Economy Brands
- Motorad: This brand is widely available but has a poor reputation among many mechanics and DIYers for inconsistency and a high failure rate. Some sources claim Motorad now manufactures thermostats for other brands, including Stant, which may explain the decline in quality. It is best to avoid these if possible.
Pro Tip: No matter which brand you buy, it's a good practice to test the new thermostat before installing it. Simply hang it in a pot of water on the stove with a thermometer. Watch to see that it opens near its rated temperature (e.g., 195°F) as the water heats up.
Aftermarket Thermostat Cost for 1978-1980 Dodge RD200
| Part Type | Price Range |
|---|---|
| New Aftermarket Thermostat | $7.33 - $56.13 |
| Thermostat Gasket (Sold Separately) | $1 - $5 |
Known Issues, Recalls & TSBs
Searches of the National Highway Traffic Safety Administration (NHTSA) database and technical service bulletin (TSB) archives found no specific recalls or bulletins related to the engine coolant thermostat for the 1978-1980 Dodge RD200. Any failure on a vehicle of this age is almost certainly due to normal wear and tear over several decades.
Frequently Asked Questions (FAQ)
What temperature thermostat should I use in my RD200?
For a stock Dodge V8 engine from this era, a 195°F thermostat is generally recommended for best efficiency and heater performance. A 180°F thermostat can be used in very hot climates or for mildly modified engines. Avoid 160°F racing thermostats for street use, as they will likely cause the engine to run too cool.
Is replacing the thermostat a good DIY job?
Yes, this is a great job for a beginner. On these Dodge trucks, the thermostat is almost always on top of the engine at the front, where the upper radiator hose connects. The job requires basic hand tools to drain some coolant, remove the two-bolt housing, and swap the part. The key is to thoroughly clean the old gasket material off both the engine and the housing before installing the new gasket.
Do I need to replace the gasket too?
Yes, always use a new gasket. Never reuse the old one. Some thermostats come with a gasket, but often you must buy it separately. Using sealant in addition to the gasket is usually not necessary unless the housing surfaces are pitted or damaged.
Do I need a "high-flow" thermostat?
For a stock engine, a high-flow thermostat is not necessary. A standard design from a quality brand will work perfectly. High-flow models from brands like Edelbrock are designed for engines with high-volume water pumps and other performance cooling system modifications.
Technical Specifications
Standard Temperature: 180°F or 195°F. The thermostat is typically located where the upper radiator hose connects to the engine intake manifold.
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.