Engine Coolant Thermostat Guide for 1975-1989 Dodge W100
Keep your classic Dodge W100's engine running at the right temperature by choosing the correct thermostat.
- A failing thermostat can cause your engine to overheat (stuck closed) or run too cool (stuck open). Overheating is a critical issue.
- For a stock 1975-1989 W100, always choose a new thermostat with the factory temperature rating, usually 195°F.
- Replacing the thermostat is a simple, DIY-friendly job that takes about an hour with basic tools.
- While OEM Mopar parts are scarce, quality aftermarket brands like Calorstat and Gates are reliable choices for a stock replacement.
Is Your W100 Thermostat Failing?
A thermostat is a simple mechanical part, but it's critical. When it fails, it usually gets stuck in one of two positions: open or closed. Both can cause problems for your classic truck's engine.
Stuck Closed: The Danger Zone
This is the more serious failure. A thermostat stuck closed prevents coolant from reaching the radiator. Your engine will quickly overheat, which can lead to warped cylinder heads, blown head gaskets, and catastrophic engine damage. If your temperature gauge shoots into the red, you see steam from the engine, or hear rumbling/boiling sounds, pull over immediately.
Stuck Open: The Inefficient Failure
If the thermostat is stuck open, coolant constantly flows to the radiator. This makes it very difficult for your engine to reach its normal operating temperature, especially in cooler weather. Symptoms include the temperature gauge staying low, poor heater performance, and reduced fuel economy because the engine runs rich (too much fuel) trying to warm up.
Choosing the Right Aftermarket Thermostat
For a vehicle like the 1975-1989 W100, finding a new original Mopar thermostat is highly unlikely. The good news is that many quality aftermarket brands are available. The key is to choose the right one for your needs and avoid common pitfalls.
Always choose a thermostat with the OEM-specified temperature rating for your engine (usually 195°F). Using a lower temperature thermostat on a stock engine can negatively affect performance and efficiency.
Brand Quality Tiers for Your Dodge
Based on owner experiences and forum discussions, aftermarket thermostats can be grouped into tiers:
- Premium/OEM-Equivalent: Brands like Calorstat are often considered OEM suppliers and have a strong reputation for quality and reliability. They are designed to meet original specifications and are an excellent choice for a stock replacement.
- Reliable Aftermarket: Gates is a well-regarded brand in the aftermarket community. Many owners have used them for years with good results. Motorad's higher-end "UltraStat" line is also considered a decent option with better construction than some base models.
- Performance/High-Flow: Brands like Edelbrock, Mr. Gasket, and Mishimoto are geared towards performance applications. They often feature high-flow designs or lower opening temperatures (e.g., 180°F or 160°F). While they can be beneficial in highly modified or racing engines, they are generally not recommended for a stock daily-driven W100. Using one can lead to the engine running too cool.
Estimated Costs
| Part/Service | Estimated Cost |
|---|---|
| New Aftermarket Thermostat | $7.93 - $56.13 |
| Shop Labor | $100 - $200 |
| Total Professional Replacement | $110 - $260 |
Pro-Tip: Replacing the thermostat is a great time to also replace the upper radiator hose and flush your cooling system. It's a simple job that adds minimal cost and ensures the whole system is in good shape.
Frequently Asked Questions
Can I replace the thermostat on my W100 myself?
Yes, this is a very DIY-friendly job for a 1975-1989 Dodge W100. It typically requires basic hand tools, a drain pan, and about an hour of your time. The thermostat is usually located where the upper radiator hose connects to the engine.
What temperature thermostat should I use?
For a stock W100, you should always use the OEM-specified temperature, which is typically 195°F. Using a 180°F or 160°F thermostat can cause the engine to run too cool, leading to poor fuel economy and inefficient operation.
Are there any recalls for the thermostat on a 1975-1989 Dodge W100?
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 this specific vehicle range.
What's the most common mistake when ordering a thermostat?
The most common mistakes are choosing the wrong temperature rating or buying a "performance" thermostat for a stock engine. Another potential issue is getting the wrong diameter, so it's important to confirm the part fits your specific engine (e.g., Slant 6, 318 V8, 360 V8). Always stick to the OEM temperature for best results on a daily driver.
Should I use sealant on the gasket?
Some mechanics apply a very thin layer of a specific gasket sealant to help hold the gasket in place during installation, while others install it dry. The most important step is to thoroughly clean the old gasket material from both the housing and the engine surface to ensure a perfect seal.
Technical Specifications
Standard OEM Temperature: 195°F (verify for your specific engine). Gasket is typically required.
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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.