Dodge B100 Engine Coolant Thermostat Guide: 1975-1980
Keep your classic B-Series van's engine from overheating or running too cold with the right thermostat.
- A thermostat stuck closed will cause rapid overheating and can destroy your engine; pull over immediately.
- A thermostat stuck open will cause the engine to run cool, resulting in poor heat and bad fuel economy.
- For a stock van, a standard 195°F thermostat from a reputable brand like Gates is a reliable choice.
- This is a very easy DIY job for a home mechanic; always replace the gasket to prevent leaks.
Is Your B100's Thermostat Failing?
A thermostat is a simple mechanical part that wears out over time. After decades of service, the one in your Dodge B100 can fail in one of two ways: stuck open or stuck closed. Each has distinct symptoms.
Thermostat Stuck Closed
This is a critical failure that can cause severe engine damage. If you notice these symptoms, pull over and shut off the engine as soon as it is safe to do so.
- Engine Overheats Quickly: The temperature gauge will climb into the red zone, often within minutes of starting the van.
- Boiling Sounds: You may hear gurgling or boiling noises from the engine bay as the trapped coolant boils.
- Steam from Under the Hood: As pressure builds, hot coolant and steam may be forced out of the radiator cap or overflow tank.
- Sweet Smell: The smell of hot or burning coolant is a strong indicator of an overheating issue.
Thermostat Stuck Open
This failure is less dangerous to your engine but should still be fixed promptly.
- Engine Never Warms Up: The temperature gauge stays on the low end, even after driving for a while.
- Heater Blows Cold Air: Because the engine isn't reaching its proper temperature, the coolant isn't hot enough for the heater to work effectively.
- Poor Fuel Economy: An engine that runs too cool is inefficient, leading to a noticeable drop in gas mileage over time.
Choosing the Right Aftermarket Thermostat
For a classic vehicle like the 1975-1980 B100, original Mopar thermostats are no longer available from dealers. Aftermarket parts are your only option. A quality aftermarket part will perform as well as, or better than, the original 1970s technology. However, brand quality varies significantly based on owner experiences in Mopar forums.
Brand Quality Tiers
Standard Replacement (Recommended for Stock Vans):
- Gates: Consistently viewed as a reliable and safe choice for cooling system components.
- Motorad: A major manufacturer that supplies parts to many other brands, including some formerly top-tier names like Stant. Reviews are very mixed; some units work perfectly, while others fail prematurely. It's a budget-friendly option, but be aware of the inconsistent quality reports.
Performance Options (Consider for Modified or Heavy-Use Vans):
- Edelbrock: Known for durable construction with brass, copper, and stainless steel components. Generally well-regarded in high-performance applications and considered a reliable, if more expensive, choice.
- Mr. Gasket: These high-flow thermostats have very polarized reviews. Some owners report they hold a precise temperature perfectly, but many others have experienced failures right out of the box or after a short time. This suggests potential quality control problems.
Pro Tip: Test Before You Install. Regardless of the brand you choose, it's a wise practice to test the new thermostat before installation. Place it in a pot of water on the stove with a thermometer. Watch to see that it opens at its rated temperature as the water heats up. This simple step can save you from having to do the job twice.
Cost to Replace a Dodge B100 Thermostat
| Part Type | Cost Range |
|---|---|
| New Aftermarket Thermostat | $7.33 - $56.13 |
| Shop Labor Estimate | $100 - $150 |
Frequently Asked Questions (FAQ)
Is this a good DIY job for a beginner?
Yes. Replacing the thermostat on the Slant-6 or V8 engines in these vans is a very straightforward job. It's typically located where the upper radiator hose meets the top of the engine and is held on by two bolts. Basic hand tools are all that's required.
What temperature thermostat should I use?
For a stock B100, a 195°F thermostat is generally the correct choice for overall efficiency and heater performance. A 180°F thermostat can also be used, especially in very hot climates. Avoid low-temperature (160°F) "racing" thermostats for a street-driven van, as they can prevent the engine from warming up properly, causing increased engine wear.
Do I have to replace the gasket?
Yes, always use a new gasket. Re-using the old one will almost certainly cause a coolant leak. Many thermostats come with a new gasket, but check before you buy. For extra insurance against leaks, you can apply a thin layer of thermostat housing sealant to both sides of the gasket.
My van still overheats after replacing the thermostat. What's wrong?
If the problem persists, you may have air trapped in the system. Try parking the van on an incline (nose up), removing the radiator cap (when the engine is cold!), and letting it run to "burp" the air out. Other potential causes include a clogged radiator, a failing water pump, a collapsed radiator hose, or a bad fan clutch.
Are there any recalls for the thermostat on my Dodge B100?
No. Searches of the National Highway Traffic Safety Administration (NHTSA) database show no recalls or technical service bulletins (TSBs) for the thermostat on 1975-1980 Dodge B100 vans. Any failure today is due to the part's age and normal wear.
Technical Specifications
Common temperature ratings for the 1975-1980 Dodge B100 are 180°F and 195°F. The correct thermostat diameter is typically 2.125 inches for Mopar small block and big block engines of this era.
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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.