Dodge D350 Engine Coolant Thermostat: A Guide for 1981-1988 Models
Keeping your D350's big engine at the right temperature starts with this small, crucial part.
- A failing thermostat can either stick open (engine runs cool) or stick closed (engine overheats); overheating is a critical emergency.
- For the V8 engines in the D350, a 180°F or 195°F thermostat is the correct choice for proper engine operation.
- Brand quality is mixed; consider premium standard brands like Edelbrock or Calorstat, and always test a new thermostat in hot water before installation.
- Replacement is simple and inexpensive, making it a good first step when troubleshooting cooling system issues.
Is Your D350 Thermostat Failing?
A thermostat is a simple mechanical part, but when it fails, it can cause problems ranging from annoying to catastrophic for your truck's engine. Thermostats typically fail in one of two ways: stuck open or stuck closed.
Critical Failure: Stuck Closed
This is the most dangerous type of failure. The thermostat fails to open, trapping hot coolant inside the engine block. This will cause rapid overheating, which can lead to warped cylinder heads, blown head gaskets, and severe engine damage. If your temperature gauge spikes into the red, pull over and shut off the engine immediately.
Common Failure: Stuck Open
A thermostat stuck in the open position allows coolant to flow to the radiator constantly. This prevents the engine from reaching its proper operating temperature. Symptoms include a temperature gauge that never reaches the middle of the normal range, poor heater performance in the cab, and potentially worse fuel mileage. While less dangerous than a stuck-closed failure, it should still be addressed to prevent long-term engine sludge buildup.
Choosing the Right Aftermarket Thermostat
For a classic workhorse like the 1981-1988 D350, reliability is key. You don't need the most expensive part, but you should avoid the cheapest no-name options. Aftermarket thermostats for your truck generally fall into a few categories.
Brand Quality Tiers
- Standard Replacement (Tier 1): Brands like Gates and Motorad are widely available. They are designed to meet original factory specifications. However, forum discussions suggest that quality can be inconsistent, with some users reporting early failures. It's worth noting that Motorad often manufactures thermostats for other brands, including Gates and even some OEM Mopar parts for newer vehicles.
- Premium & High-Performance (Tier 2): Brands like Edelbrock, Mishimoto, and Mr. Gasket offer 'high-flow' designs. These are built to allow more coolant to pass through when open, which can be beneficial for modified or hard-working engines. Edelbrock generally receives positive reviews for quality. Mr. Gasket reviews are very mixed, with some users loving them and others reporting them failing right out of the box. Calorstat is another brand that gets positive mentions for holding stable temperatures, especially under load.
Pro Tip: Test Before You Install
It's a classic mechanic's trick for a reason. Before installing any new thermostat, suspend it in a pot of water on the stove with a thermometer. Heat the water and watch to see that the thermostat opens near its rated temperature (e.g., a 180°F thermostat should start opening around 180°F). This simple test can save you from installing a defective part.
Cost of a New Thermostat for Dodge D350
| Part Type | Estimated Cost |
|---|---|
| New Aftermarket Thermostat | $7 - $56 |
| Shop Labor for Installation | $75 - $150 |
Cost estimates are for parts and labor and may vary based on your location and chosen supplier.
Frequently Asked Questions
What temperature thermostat do I need for my D350?
For the V8 engines (5.2L/318ci and 5.9L/360ci) common in these trucks, a 180°F or 195°F thermostat is typically standard. A 195°F thermostat is often preferred for better engine efficiency and heater performance. Check your vehicle's specific requirements, but either should work well. Using a lower temperature thermostat (like 160°F) is generally not recommended unless you have a specific, modified application, as it can negatively impact fuel economy.
Can I just remove the thermostat and run without one?
No, this is a bad idea. Running without a thermostat will cause the engine to run too cool, leading to poor performance, increased fuel consumption, and accelerated engine wear and sludge buildup. The cooling system is designed to operate with a thermostat regulating the temperature.
What is a 'fail-safe' thermostat?
These are designed to lock in the open position if they fail, preventing a catastrophic overheating event. While the idea is good, some mechanics find them prone to 'false fails,' where they lock open without an actual overheating event, causing the exact symptoms of a standard stuck-open thermostat. For a simple, robust truck like the D350, a quality standard-design thermostat is often the most reliable choice.
Do I need to replace the gasket too?
Yes, absolutely. Always use a new gasket when replacing the thermostat to prevent coolant leaks from the housing. Some thermostat kits come with a new gasket. If not, purchase one separately. Make sure the mating surfaces on the engine and the thermostat housing are clean and smooth before installing the new gasket.
Technical Specifications
The most important specification is the temperature rating, typically 180°F or 195°F. Ensure you get the correct size/design for your specific engine (V8 vs. Slant-6). High-flow designs are available but not required for stock applications.
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.
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