Engine Coolant Thermostat Guide for 1977-1981 Dodge D150
Keep your classic Dodge D150's engine temperature in check with the right thermostat.
- The correct thermostat for a stock 1977-1981 D150 is 195°F to ensure proper engine warm-up and performance.
- A failing thermostat can get stuck open (engine runs cold) or stuck closed (engine overheats). Overheating is a critical issue that can cause major engine damage.
- Many aftermarket brands like Stant and Gates may be re-boxed Motorad parts, with inconsistent quality reported by users.
- It is highly recommended to test any new aftermarket thermostat in hot water before installation to verify it opens at the correct temperature.
Is Your D150 Thermostat Failing?
A thermostat is a simple mechanical part that can fail in two ways: stuck open or stuck closed. The symptoms are usually obvious if you know what to look for.
Stuck Closed Symptoms
- Engine Overheating: This is the most common and dangerous symptom. The temperature gauge will climb into the red, and you may see steam from the engine. A closed thermostat traps coolant in the engine, preventing it from reaching the radiator to cool down.
- Coolant Leaks: Extreme heat and pressure from overheating can cause coolant to boil over and leak from the radiator overflow or other weak points in the cooling system.
- Rumbling or Gurgling Noises: You might hear sounds from the radiator or engine as the coolant boils.
Stuck Open Symptoms
- Engine Takes Too Long to Warm Up: Your temperature gauge may stay on cold for a long time or never reach the normal operating range.
- Poor Heater Performance: The heater in your cab blows lukewarm or cold air because the engine coolant never gets hot enough.
- Decreased Fuel Economy: An engine that runs too cool is inefficient and uses more fuel.
Choosing the Right Aftermarket Thermostat
For a 1977-1981 Dodge D150, finding a quality aftermarket thermostat can be tricky. Many brands on the market are actually made by the same manufacturer and re-boxed. Quality can be inconsistent, even with well-known names.
Aftermarket Brand Tiers
Tier 1 (Recommended):
- Calorstat: In forums discussing thermostats for Dodge trucks, Calorstat is mentioned as a reliable option that holds temperature accurately.
Tier 2 (Use With Caution):
- Gates, Motorad, Stant: These brands are widely available. However, many sources indicate that Stant and Gates are often re-branded Motorad thermostats. While some users have no issues, many report premature failures or incorrect temperature regulation right out of the box. If you choose one of these brands, it is highly recommended to test the thermostat in a pot of boiling water to ensure it opens at the correct temperature before you install it.
Tier 3 (Performance/Specialty):
- Edelbrock, Mr Gasket: These are often marketed as "high-flow" thermostats. While they may be suitable for highly modified engines, they are not necessary for a stock D150. Some users have reported early failures with Mr Gasket high-flow units. Additionally, if your truck has an aftermarket intake manifold, like one from Edelbrock, you may need a different size thermostat than the stock one.
Always Test Before You Install
Given the reports of inconsistent quality among aftermarket brands, it's a smart move to test your new thermostat before installation. Suspend the thermostat in a pot of water on the stove with a thermometer. Watch to see that it opens fully as the water temperature reaches the rating stamped on the part (e.g., 195°F). This simple step can save you from having to do the job twice.
Expected Costs
Replacing the thermostat is one of the more affordable repairs you can make. The parts are inexpensive, and labor is minimal.
| Part or Service | Estimated Cost |
|---|---|
| New Aftermarket Thermostat | $7 - $57 |
| Thermostat Gasket | $2 - $10 |
| Shop Labor | $90 - $150 |
Frequently Asked Questions
What temperature thermostat should I use for my D150?
For a stock Dodge D150 with a 225 or 318 engine, a 195°F thermostat is the correct factory specification. Using a cooler 180°F or 160°F thermostat can lead to poor fuel economy, reduced heater performance, and increased engine wear over time.
Do I need to replace the gasket too?
Yes. Always use a new gasket when replacing the thermostat to prevent leaks. Some thermostat kits include a new gasket. It's also wise to use a thin layer of gasket maker sealant on both sides of the gasket to ensure a perfect seal on the old metal surfaces.
Can I just remove the thermostat if it fails?
No. Running without a thermostat will cause the engine to warm up very slowly and likely never reach its proper operating temperature. This hurts fuel economy and causes the engine computer (on later models) to stay in an open-loop mode, which can lead to long-term engine problems.
Is this a difficult job to do myself?
No, this is a great job for a beginner. The thermostat is usually located on the top of the engine at the end of the upper radiator hose, making it easy to access. The job requires basic hand tools and should take less than an hour.
Technical Specifications
Standard Temperature: 195°F (90.5°C). Note that some aftermarket intake manifolds may require a larger diameter thermostat than the stock version.
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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.