If the cooling system is contaminated, then the coolant must first be drained and the cooling system must be rinsed.
Contamination may be:
- Oil (defective cylinder head gasket)
- Rust (internal corrosion of engine)
- Aluminium (internal corrosion of radiator)
- Foreign particles (additives/sealant)
- Foreign particles (defective water pump)
Depending on the degree of soiling, the cooling system is cleaned with hot water or with a special rinsing liquid. Depending on vehicle manufacturer and symptom, there are various approaches to rinsing. Audi specifies a special rinsing liquid for rinsing if the coolant is rusty brown and the heating power is insufficient. For the multiple rinsing process, the thermostat must be dismantled and the heating power must be measured before and after the rinsing.
With regard to its models Corsa, Vectra and Omega up to model year 1997, Opel/Vauxhall notes that a clogged radiator may be the cause of excessively high engine temperature. In that case, the system should be rinsed with hot water (> 50 °C) and, in addition to the radiator, all coolant-contacting parts (heat exchanger, cylinder head etc.) should be replaced. The degree of contamination and the vehicle manufacturer’s instructions thus specify the method and the rinsing agent to be used. It should at any rate be observed that due to the design (e.g. flat tube) of modern cooling systems not all components can be rinsed and therefore need to be replaced.
This applies in particular for the following components:
- Electrical valves
- Heat exchanger
If the coolant level in the expansion tank cannot be checked due to the contamination (oil, rust), then the tank must likewise be replaced. Thermostat and the closing cap should be replaced as a rule. If special cooling system cleaners are used, then care must be taken that they do not attack sealing materials and do not get into the groundwater or are disposed of via the oil separator. The cleaning agents must be collected together with the coolant and be disposed of separately. After rinsing, the system must be filled with coolant following the vehicle manufacturer’s instructions, bled and checked for function and tightness.