Draining Antifreeze: 671 Detroit Diesel Boat Engine Maintenance Guide

The Detroit Diesel 6-71 engine is a robust and reliable engine, commonly found in boats and tugs. While these engines are built to last, proper maintenance is key to ensuring their longevity. One important aspect of maintenance is draining and replacing the engine coolant, which should be done when it becomes old or contaminated. This process can be tricky due to the cramped engine spaces and the toxicity of the coolant. It is important to capture the waste coolant and dispose of it properly. Additionally, for winter storage, it is crucial to drain the engine and add antifreeze to prevent a cracked block. This guide will provide a step-by-step procedure for draining the antifreeze and coolant from a Detroit Diesel 6-71 boat engine, ensuring a safe and efficient process.

Find the engine drain plug

To find the engine drain plug on a Detroit Diesel 6-71 engine, you'll first need to locate the serial number. This can be found on the cylinder block. The serial number will be similar to 6A18959, where the first digit indicates the number of cylinders. So, for the 671 engine, the serial number will start with a 6.

For older engines, the full engine size and series can be identified in the first three digits. For example, 671-RA63 indicates that it is a 6-cylinder member of the 71 series.

Once you've confirmed that you have the correct engine, you can refer to the engine manual or a Detroit Diesel mechanic to locate the specific drain plug for your model.

It's important to note that these engines are known for their reliability and longevity, and proper maintenance is key to keeping them in good condition. This includes regular oil changes, as these engines tend to spill oil during their use. Only certain types of lubricating oil should be used, such as a high-detergent lubricant made for heavy-duty use.

Additionally, when it comes to troubleshooting and repairs, it's recommended to consult a professional familiar with these engines, as they have unique characteristics that differ from four-stroke engines.

Place a pan under the plug opening

Let the engine drain for a while; there are a lot of jackets and crevices and that heat exchanger to empty. A lot may dribble out. It is recommended that you fill the engine with fresh water and run it for a few minutes to circulate and rinse it. Then, when the engine has cooled enough, repeat the above steps before you refill with fresh coolant.

When replacing your engine coolant, check your boat's engine manual for guidelines on which coolant to use. There are different types of coolant, and you will need to mix the coolant with the correct proportion of water. Most specify 50%/50% water to coolant for optimal heat removal and freeze protection.

Open the drain plug

To open the drain plug on your 6-71 Detroit Diesel boat engine, you'll need to locate the engine drain plug. This can be tricky, as it usually looks like another knob or protrusion on the engine block. Refer to the engine manual in your owner's manual to find the exact location—it may be labelled as "Block Drain" or "Coolant Drain".

Once you've located the drain plug, follow these steps:

• Place a flat catch pan, like an oil change pan, under the plug opening. Make sure it's positioned to catch any overspill, and that the pan is big enough to capture all the coolant.
• Slowly open the drain plug. The coolant will start to flow out. If the flow is low, open the coolant fill cap at the top of the engine.
• If your drain pan is full, close the plug, empty the pan into sealable waste storage containers, then replace the pan under the drain and continue.
• Let the engine drain completely. There are a lot of jackets and crevices, and the heat exchanger will need time to empty.
• (Optional) Using the exhaust/blower side of a shop vacuum, put the hose on the fill cap hole to blow out any remaining coolant. You may need to seal the gap with rags or your hand to increase the pressure.
• Transfer the waste coolant to storage bottles.
• Dispose of the waste coolant properly. Contact your local sanitation department, trash hauler, or marina office for disposal instructions.

Remember, engine coolant is toxic and must be handled and disposed of carefully. It can cause blindness or death and may be attractive to pets and children due to its sweet taste and smell.

Let the engine drain

Using the exhaust/blower side of a shop vacuum is optional. Put the hose on the fill cap hole to blow out any remaining coolant. You may need to seal the gap between the hose and the fill cap hole edge with rags or your hand to get more effective pressure.

Transfer the waste coolant to storage bottles

Transferring the waste coolant to storage bottles is the final step in the process of draining the engine coolant. This step is important as it ensures the waste coolant is disposed of properly and does not end up in the bilge or overboard. It is recommended to use old coolant jugs as storage bottles, as they are perfect for holding the waste coolant.

Once you have collected the waste coolant in the sealable containers, you can then dispose of it properly. It is important to note that engine coolant is toxic and must be handled with care. Most marinas have a disposal area for waste coolant, and you can also take it to an appropriate disposal facility or a service station that accepts waste coolant. Some municipal or regional household hazardous waste handling centers also accept waste coolant.

It is worth mentioning that propylene glycol, which is used in boat antifreeze, can be recycled, but this is typically done in industrial volumes. Collection centers may recycle small amounts, but it is not common.

Frequently asked questions