Replacing a Block Heater on a Detroit 671 Engine

[MikePhua]

The Detroit Diesel 671 engine, part of the legendary 71 series, is known for its robustness and reliability. It’s often found in heavy-duty applications like trucks, buses, marine vessels, and power generators. However, like any piece of machinery, even a stalwart engine like the 671 can face issues—one of which is the failure of the block heater. In colder climates, a block heater is essential for ensuring that the engine starts smoothly and efficiently. Replacing this vital component is not overly complicated but requires a few key considerations to ensure proper installation and function.
Understanding the Detroit 671 Engine
The Detroit Diesel 671 is a two-stroke, inline, 6-cylinder engine that has been in production since the 1940s. Over the decades, the 671 has been recognized for its power and reliability, commonly found in industrial, commercial, and military vehicles. Its two-stroke design gives it an advantage in high-revving applications, making it highly efficient in specific industries, such as marine and mining.
The 671 engine features a robust and relatively simple mechanical design that has earned it a reputation for longevity and ease of maintenance. Despite being phased out by newer models, the 671 engine still maintains a strong presence in the second-hand market, with many units still running in the field today. However, even the most durable engines can face issues related to electrical components, including the block heater.
Why Block Heaters Are Important for the Detroit 671
A block heater serves as an essential component in cold climates, especially when starting diesel engines like the Detroit 671. Diesel engines rely on high compression to ignite the fuel, and when the engine is cold, the necessary heat for compression can be difficult to achieve. A block heater keeps the engine's coolant warm before starting, ensuring easier starts and reducing the wear on the starter motor and battery.
In extreme temperatures, the absence of a functioning block heater can cause difficulty starting the engine, increased engine wear, and potential damage to critical engine components. Therefore, replacing a faulty block heater as soon as possible is crucial for maintaining the engine’s performance and longevity.
Symptoms of a Failing Block Heater
Before replacing the block heater, it’s important to diagnose the issue correctly. Some common symptoms of a failing block heater include:

• Difficulty Starting the Engine in Cold Weather: The most common sign of a malfunctioning block heater is trouble starting the engine in colder temperatures, especially in sub-zero conditions.
  
• No Power to the Block Heater: If there is no visible indication of power when the heater is plugged in, such as a lack of warmth in the block or a tripped circuit, the block heater may need replacing.
  
• Visible Leaks: Leaks around the heater, especially if coolant is visibly escaping, may indicate that the block heater’s seals are worn out or that the heater itself is cracked or damaged.
  

Steps to Replace the Block Heater on a Detroit 671
Replacing the block heater in the Detroit 671 requires some mechanical knowledge, but it is not an overly complex process. Here is a general step-by-step guide for replacing the block heater:
1. Preparation

• Ensure Safety: Always begin by turning off the engine and disconnecting the battery. If the engine has been running recently, give it time to cool down before proceeding with the repair.
  
• Locate the Block Heater: On most Detroit 671 engines, the block heater is typically located on the engine block, usually near the lower part of the engine. This heater is typically a threaded element that is screwed into the block.
  

2. Draining the Coolant
To replace the block heater, you’ll need to drain the coolant system to avoid spillage during the removal process. Make sure to drain the coolant into a clean container to reuse it, if possible. You may want to replace the coolant at the same time, depending on its condition.
3. Remove the Old Block Heater

• Disconnect the Electrical Wires: If your block heater is electrically connected, start by disconnecting the power supply from the heater. It’s typically a plug-in type with a cord running to a power source.
  
• Remove the Heater: Using the appropriate tools (such as a socket wrench or impact driver), unscrew the block heater from its threaded location. Be mindful not to damage the threads or surrounding area during removal.
  

4. Install the New Block Heater

• Thread the New Heater: Take the new block heater and screw it into the same location where the old one was removed. Make sure it is threaded securely but be careful not to overtighten it, as this could cause damage.
  
• Reconnect the Electrical Wires: If the heater has an electrical connection, reconnect the wiring or plug it into the power supply. Ensure all connections are tight and secure.
  

5. Refill the Coolant System
After the new block heater is installed, refill the coolant system with fresh coolant if needed. Ensure that the system is filled to the appropriate level and that there are no air pockets in the system.
6. Test the Block Heater
Plug the heater back in and check for proper operation. Let the engine sit for a while and check if the coolant is warming up. You should be able to feel the warmth coming from the block heater after about 15-30 minutes of use. If the heater is functioning correctly, the engine should start without difficulty.
Tips for Preventing Future Block Heater Problems
To prolong the life of your new block heater and ensure reliable performance, here are some maintenance tips:

• Regularly Check the Block Heater: Periodically inspect the block heater for any signs of wear, cracks, or leaks. Ensure that the electrical connections are secure.
  
• Keep the Electrical Connections Clean: Dirt, rust, or corrosion on the block heater’s electrical connections can cause failures. Clean and maintain the connections regularly.
  
• Use the Heater Properly: Avoid leaving the block heater plugged in for extended periods, as overuse can lead to premature failure. It’s best to use it only as needed during cold weather.
  
• Install an Indicator Light: Consider installing an indicator light or power monitor to easily check whether the heater is operating when plugged in.
  

Conclusion
Replacing the block heater in a Detroit 671 engine is a straightforward process that can have a significant impact on the engine's performance in cold weather. By following the correct steps for installation and taking preventive measures, you can ensure that your engine starts easily and operates efficiently, even in extreme temperatures.
Block heaters are essential for maintaining the longevity of your Detroit 671, particularly in colder climates. With regular maintenance and timely repairs, you can keep your Detroit Diesel engine running smoothly for years to come.