When you work on the engine's cooling circuit, there are several things you should be mindful of. This doesn't just apply to the routine changing of coolant but also to replacing faulty components (such as the water pump, thermostats, and radiators), fixing leaks in hoses or connections, and installing an auxiliary heater. Careful work is of the utmost importance.
Changing the coolant isn't as simple as just draining and refilling anymore. You should closely inspect the old coolant when changing it and check for any contaminants. Foreign substances or objects like oil, rust, scale, and aluminum particles can indicate defects in components or even parts outside of the cooling system. In such cases, the cooling system must be flushed.
As a general rule: Vehicle manufacturers provide specific procedures and the type of flushing agent to be used, depending on the level of contamination. For some modern cooling systems, certain components may need to be replaced due to their design, as they can no longer be flushed effectively.
Note: When replacing components and after opening hose and plug connections, make sure to replace all old seals. This is often overlooked because, for many quick-release connectors on thermostat housings, these seals are located in the counterpart of the connecting hose and aren't directly visible from the outside.
Tip: For MAHLE's thermal management products marked with SIMPLE FIT, accessories such as O-rings, seals, or screws are already included in the package.
The traditional method of refilling through the reservoir or radiator cap isn't physically feasible anymore. This is because often the radiator or other components are at the same level as the vehicle's engine or even below it. Moreover, the cooling systems of modern cars are so intricately designed that the coolant can't naturally flow into every nook and cranny. This inevitably leads to air pockets in the system! These pockets significantly reduce the circulation of the coolant – which can result in engine overheating and severe damage.
Thus, the only professional and therefore safe method is vacuum-filling the cooling system. Another advantage to this method is that if a sufficient vacuum isn't achieved in the cooling circuit, there's likely an issue with the system. Vacuum bleeding devices use a Venturi nozzle and shop compressed air to draw out all the air from the cooling system.
Afterward, the new coolant, approved by the vehicle manufacturer, is drawn bubble-free into the cooling circuit by the vacuum. It's essential during this process to maintain the correct ratio of water to coolant. Ideally, you should mix the coolant with 50% distilled water to ensure adequate freeze protection. As always, it's vital to follow the vehicle manufacturer's guidelines and not mix different coolants together.
By the way, the vacuum only pulls out air and not the coolant from the system. You can't drain the cooling circuit using a vacuum.