Drivers Education

Mechanic’s Guide to Drain Coolant from Engine Block

When flushing coolant or antifreeze, you might want to drain it from the engine block also. Thus, this article shows the steps regarding how to drain coolant from engine block.

You can drain engine coolants by opening the radiator petcock. However, if you find no petcock, you would have to remove the lower hose from the engine block to drain coolant/antifreeze. Most of the time, a small amount of oil is left in the block, which you can flush using water before replacing the coolant.

You might also see coolant remnant in the dash heater core. But you do not necessarily have to remove all drops of coolant to change the coolant. The coolant you can remove from the car is enough, and it’s okay to add new coolant even with remnants in the reservoir.

Meanwhile, below are the steps to drain coolant from the engine block:

  1. Turn Off Engine

First, turn off the vehicle engine and allow it to stay in an off state until the radiator cap cools off. Do not attempt to open the cap while the engine is heated. Note that pressure builds up from the radiator and even reaching the hose from the engine block is dangerous.

  1. Locate Coolant Drain Plug

Where is the coolant drain plug on the engine block? You can find the coolant drain plug on the rear of the engine block, typically somewhere near the bottom, but not the exact position with the oil pan. You can find it closer to the flywheel housing, the outer part of the engine pan. It usually looks like bolts in the block that do not hold anything.

  1. Pull Out the Hose

Next, pull the hose from underneath the radiator for the coolant to pour out. You may use a bucket to collect the worn-out coolant/antifreeze. You may now remove the radiator cap and flush it with water using the regular hose.

  1. Idle the Engine

Some experts recommend idling the car engine for a few minutes after draining the coolant from the engine block. Meanwhile, how long can a car remain idle?

  1. Add More Coolant

Turn off the idling engine and add coolant. Make sure to replace the hose from the engine block to avoid draining the new coolant. If there is still coolant, you can allow it a longer period to drain out before replacing the hose.

  1. Check for Leaks

It is advisable to check the coolant system for leaks when draining worn-out coolant or antifreeze from the engine block. Make sure to inspect the clamps/hoses. You may have to replace the thermostat, which wears off over time.

Sometimes, an overflowing hose removes excessive coolant from the engine block. You might find a coolant puddle underneath your vehicle if the hose overflows. Also, overfilling coolant or antifreeze can damage electrical components, especially if the overflow touches the engine wiring.

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How much coolant is in the engine block?

Typically, there are between 1½ and 2 gallons of coolant in the engine block. The reason is that you would normally find this amount when draining coolant into a basin or fluid bucket. Meanwhile, how much coolant does your car need when empty?

Does car engine coolant need to be drained?

Yes, a car engine coolant needs to be drained after a while. Most of the time, coolant older than 5 years in a car may be okay. Depending on the automaker, the coolant might lose its protective properties after 5 years.

If your car coolant has not been changed in 10+ years, or you are not sure about any recent changes, you can flush and replace coolant or antifreeze.

Note that old coolant can result in rusty metals and circulate dirt across the engine, which causes degrades the vehicle. It can also cause corrosion.

Another reason for coolant replacement is overheating. Yes, coolant can cause overheating in a car when it becomes dirty, having too much build-up, which prevents it from moving through the pump.

Note that you do not necessarily have to change your car coolant after 5-10 years. Your owner’s manual specifies the manufacturer’s recommended interval, which you should follow.

In some older Asian vehicles, manufacturers recommend draining or flushing coolant after 2 years, notwithstanding the mileage. American vehicle manufacturers may recommend 150,000 miles or 10 years, depending on the vehicle. Some Mercedes cars, for instance, would have the coolant drained/filtered and reused permanently.

Note also that the coolant you use must match the manufacturer’s specifications. For instance, some coolants are designed for high performance, and we also have coolants for hot weather. Not all coolants enhance performance in specific cars. For example, it may not be OK to use coolant/antifreeze designed for Grand Cherokee on a Honda Civic. Some GMs will need Dex-Cool compared to most European cars that use various fluids.

What Happens if You Don’t Change Car Coolant?

What happens if you don’t change car coolant is that the corrosion inhibitors will eventually stop working. Moreover, the internal radiator and heater core can plug up with corrosion and gunk.

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Also, the cooling system will underperform when old coolant builds up dirt, which clogs up the radiator, causing the engine to overheat since it can’t circulate easily. Of course, the heater will release less heat after clogging partially.

The heater and radiator can corrode, which results in a leak that disposes of coolant from the vehicle. When there is a loss of coolant, the engine cooling system malfunctions, and the interior overheats.

Where is the coolant drain plug on engine block?

A lot of home mechanics drain and replenish their engine’s coolant, only to realize that it makes no difference in the engine’s capacity to maintain the correct operating temperature. The issue is not the operation they are attempting to complete, but rather their inability to locate the coolant drain plug on engine block that must be opened as part of the flushing process.

Engine block drains allow you to drain coolant from the engine block, however the radiator petcock will only allow you to drain the radiator and lines. If you have only drained the radiator and lines, you have only partially completed the job.

The coolant drain plug is located on the rear of the engine block, often at the bottom, but not in the same precise location as the oil pan. Precisely, it is located closer to the flywheel housing, on the engine pan’s exterior. It typically resembles bolts in the block that do not hold anything.

Note: If you drain the coolant, be careful to place it in a suitable container and dispose of it properly. It is toxic to animals and will contaminate ground water. Given your high mileage, it is likely that your radiator is clogged and requires professional cleaning or replacement.

Is it necessary to drain coolant from engine block?

The direct answer to the question is that it is necessary to drain coolant from engine block. The majority of the time, coolant older than five years may be okay in a car. After five years, depending on the manufacturer, the coolant may lose its protective features.

If you have not replaced your car’s coolant in 10 or more years, or if you are unsure if it has been replaced recently, you can drain and replace the coolant. Note that outdated coolant can produce rusty metals and spread dirt throughout the engine, which causes the car to decline. Also, it can cause rusting.

Overheating is another reason to drain coolant from engine block. Yes, a car’s coolant can cause overheating if it becomes too dirty and clogged, preventing it from passing through the pump. Note that you are not required to replace your car’s coolant after 5 to 10 years. You should adhere to the manufacturer-recommended interval specified in your owner’s manual.

In some older Asian cars, the manufacturer recommends draining the coolant after two years, regardless of mileage. On the other hand, American automakers may recommend 150,000 miles or 10 years. For some Mercedes vehicles, you can permanently drain, filter, and reuse the coolant.

Final Thoughts

The steps to drain coolant from the engine block will differ slightly depending on the car. For better accuracy, you should follow the user’s manual to drain/flush your car’s cooling systems.

As mentioned earlier, do not remove the radiator cap or disconnect the hose from the engine block while the engine is hot. It can result in a splash that causes burns. When the engine cools off, take off the radiator cap and remove the hose underneath the engine block for the coolant to drain.

If you are unsure how to drain coolant from the engine block, consult a mechanic. They will also identify issues that require fixes and make recommendations.

Latest posts by Bernard Juchli (see all)

Bernard Juchli

Bernard Juchli is an experienced racer, mechanic and team owner who trusts Avon Tyres.Bernard is the lead driver and force behind his Big Dog Garage Race Team. He is the General Manager and Chief Mechanic of Jay Leno’s Garage. Bernard and his crew of seven are responsible for all repairs, restoration and fabrication of Jay’s incredible automobile and motorcycle collection.

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