How to fix a BMW coolant leak?


BMW coolant leak is one of the concerns of car owners. Coolant leakage, whether large or small, will have a significant impact on the operation of the internal engine. In this article, we will learn about the importance of engine lice as well as problems in the car when coolant leaks.

What is the role of BMW coolant?

BMW car engine coolant is a specialized solution capable of maintaining the ideal temperature for a car engine to operate. Using the manufacturers’ exclusive formula, the coolant solution will absorb heat emitted from the engine, increasing the boiling point of water and reducing the freezing point.

One of the important roles of BMW engine coolant is to lubricate and prevent corrosion of components. If it is not engine coolant but normal filtered water, your car engine will quickly “go away”, just because of corrosion.

The phenomenon of coolant leaking over time will cause serious consequences for cars. Insufficient cooling water will directly affect the engine’s cooling ability. When the engine operates in a state of prolonged high temperature, it will lead to a series of other serious consequences.


Signs that the BMW coolant leak

When the coolant in the BMW E46 radiator leaks, there will be some signs as follows:

  • The engine begins to overheat: The fastest way to check the heat level on a BMW is to monitor the temperature gauge. If the temperature rises too quickly, stop the vehicle immediately.
  • BMW 3 series coolant warning light is on: This is the clearest sign that the engine wants to warn that coolant is leaking.


  • There is a puddle of water under the car: This is also one of the very common signs that your car’s cooling system is having problems. You just need to touch the puddle with your finger and apply it to the white paper. If it is a cooling solution, it will be orange, pink or blue. If it is black or brown, it is engine oil, and if it is clear and colorless, it is water from the air conditioning system.
  • The vehicle cannot roll: This sign shows that the coolant is not enough to warm the engine in the winter or cool the engine at high temperature in the summer. Therefore the vehicle is forced to stop and cannot move.

Causes of BMW coolant warning light

There are several main causes of coolant leaks including:

Material of the cooling tank

The cooling water tank is made from plastic which is an unstable material and is susceptible to cracking/expansion. Like the rest of the components in your vehicle’s engine cooling system, the radiator is under constant stress from heat and pressure. The BMW E46 water tank is actually made up of two plastic cooling tanks connected to an aluminum core. As plastic ages, it can form stress cracks, especially around coolant hose attachments.

The connecting pipes are also made of plastic

As explained above, Made from plastic material, these pipes are not sustainable over time. Excessive abrasion, combined with vibration and environmental conditions, will make this pipe more susceptible to breakage. When the coolant passes through, it will be lost through small holes.

The radiator is cracked

The radiator is a component that wears out a lot due to the nature of its operation. Over time, the radiator corrodes. This is the main cause of the radiator being punctured, causing coolant to leak out.
Additionally, the gasket between the radiator and tank can wear out, causing leaks. There may also be a leak coming from one of the hoses connected to the radiator. Over time, these tubes become brittle and susceptible to damage.

The coolant cap is leaking

The cap of the cooling water tank is not only responsible for keeping the solution from escaping but also ensuring stable pressure inside the water tank. When the radiator cap operates correctly, the cap will create a protective shield, keeping the coolant tank operating well with the correct pressure.
However, over time, the radiator cap will wear out, unable to provide as good protection as the original. From there, coolant can leak outside.

Pump is broken

The water pump is responsible for circulating coolant through the system. Normally, water pumps are driven by belts. This belt connects to the engine crankshaft, but this part can corrode and leak.
The water pump itself can also be affected by external influences leading to leakage. Either way, if the pump is not working properly, coolant cannot move properly, which will cause the engine to overheat.

Effects of BMW coolant leak

If the BMW coolant leak, causing the amount of solution in the tank to be low or depleted, it will definitely cause the car’s cooling system to be interrupted. And this can have a big impact on the entire engine system of the vehicle when operating

  • Engine temperature increases beyond the allowable level: The main task of coolant is to reduce engine temperature to a moderate and safe level. So if there is a lack of cooling water, the engine will definitely get hot and the temperature will increase when operating. This can cause a fire and explosion, which is extremely dangerous.
  • Engine oil pollution: If the leak lasts for a long time at the seal or valve, the engine oil can easily mix with the coolant. This will cause the oil to lose its lubricating ability, parts will be susceptible to corrosion and the engine will not operate effectively.
  • Impact on related parts: Causes costs when having to maintain other parts as well.

Instructions for fixing BMW coolant leaks

In case of BMW coolant leak, replacement of damaged parts is mandatory. Replacing the water tank on a BMW is a simple process for the average home mechanic. It is very important to use only a mixture of Genuine BMW Antifreeze/Coolant mixed 50/50 with distilled water when filling the system at the end of this repair.


  • Safe Water
  • Engine coolant
  • Upper radiator hose, Lower radiator hose
  • Necessary tools to perform disassembly

Implementation fix BMW coolant leak steps

Step 1: Drain the radiator and remove the lower radiator hoses: The hoses are very tight and often have to be pried out. Age and temperature cause the internal O-rings to seize on the plastic radiator hose connections. If you do not intend to replace the radiator hoses during this repair, be careful during removal so as not to damage them.


Step 2: Remove the fan shroud and cooling fan: The fan shroud and cooling fan must be removed to allow enough space to remove and reinstall the water tank. The cooling fan on a BMW is difficult to remove due to the nut (clutch nut) attached to the pulley that turns it.


Step 3: Remove the BMW water tank from the car


Step 4: Install the new BMW radiator: If you have trouble reinstalling the coolant hoses and locking them in place, apply a little dish soap to the connections. This will help the pipe be installed easily. NEVER use petroleum-based oil or grease on hose O-rings. This may cause a leak.


Step 5: Fill the BMW water tank with coolant, drain and check


Then let the engine cool. Check the coolant level in the coolant tank and refill if necessary.

Above are the basic steps to fix BMW coolant warning light for all repairmen.From the instructions we provide, you can easily follow and follow. In addition, the cooling water system is also susceptible to electronic or sensor errors that are difficult to repair. Therefore, please contact Eurocartool experts for guidance and advice on troubleshooting.

In addition, you can use professional diagnostic software for BMW such as BMW ISTA D, BMW ISTA P programming software, INPA, E-sys,… to diagnose errors, code and program the vehicle.
If you are having difficulty diagnosing BMW coolant leak errors and repairing vehicle systems, please contact us via +13155472355 for advice and support.