Cold Wash Advantages:
This is the slower process, so the cleaner is in contact longer and has more chance to do the job.

Good quality tap water may be used for dilution of the cleaning fluid. The combustion and turbine areas are cold, so they get cleaned too. Highly qualified personnel may not be required (usually in helicopters a pilot must be in control when the engines are running, for safety reasons. However, maintenance personnel are permitted to turn the engine on the starter for a cold wash).

There is a time penalty as washing usually cannot be carried out until 15–30 minutes after engine shutdown because of engine temperature.
Component wear. Starter motors are subjected to extra cycles.
Dirty washing fluid is expelled from the exhaust onto the surrounding area.
Corrosion. Most washing fluids must be rinsed out with water, then the engine must be hot-run to dry out in an attempt to minimise corrosion.
Oil contamination. Some engines have air-blown sealing arrangements which only work at high engine speeds. Cold washing can allow the oil system to become contaminated with cleaning solution. The water thus admitted may be removed by hot-running the engine until the water is boiled off.
Disposal of effluent can be costly.

Hot Wash Advantages:
Speed of operation.
No engine shutdown needed.
No mess, as the washing fluid evaporates in the exhaust stream.
No effluent disposal necessary.
Less risk of corrosion, as all moisture is dried out.
Air-blown seals work properly, preventing ingress of fluid into oil.
Fewer starter cycles.

Very short dwell time, so a powerful cleaner is needed.
Selection of flow rate is critical. Too low a rate will not clean properly. Too high a rate may cause blade damage or flameout.
Fire risk. Flammable cleaners containing solvents can act as fuel, overspeeding the engine and causing massive damage.
Helicopter application usually requires a pilot to be present.
Attack of turbine materials at high temperatures is possible if washing fluids with poor formulation or manufacturing standards are used. Component failure may also be caused by these materials blocking turbine blade cooling holes. The presence of salt carried through from the compressor may add to this risk.
Demineralised water needed for dilution of cleaning fluid.
Hot washing is prohibited on some engine types.

Both methods have their advantages. We feel that cold washing is simpler and may give a better clean. Hot washing is useful where engine shutdown is undesirable or speed of operation is required.
In general, operators should follow the engine manufacturer’s instructions.