New posts (Nov 2011) on Autopia Detailing Wiki

Avoid the [I cleaned engine and now it won't start] scenario by covering electrical / electronic and various other parts prior to using any cleaning products, sprays or water. It unsure either protect with a covering and /or use WD-40 water repellent (keep away from heat, sparks and all other sources of ignition)

The most important electrical components are sealed to be ‘water resistant’ or splash proof to resist water ingress that is to say against low pressure, water splashing upwards from the road that is encountered in the course of daily driving conditions, despite their coverings they are not ‘waterproof’. Rain or water splashed up into the engine is at very low pressure, very different from a pressurised hose or steam
Allow the engine to cool down; cold water on a hot engine will cause thermal shock, which could cause the block to fracture. Allow the engine to run while you are using a water spray. Then leave it running for approx five minutes after you are finished spraying. This allows any water that remains to evaporate with the heat from combustion

As long as you use common sense by avoiding a direct strong stream of water (or a pressure washer / steamer at close range) directly into these components, you will be fine.

• Alternator
• Alarm Housing
• Intercooler
• Battery terminals (if not covered already)
• Induction kit cone (if you have one)
• Coil packs
• Electronic control units (ECU)
• GM Opti-Spark Distributor
• On-Board Diagnostics (OBD) port
• Air intake systems (exposed air filters) can be covered with plastic wrap and a rubber band
• Avoid getting water in the spark plug recesses

Notes:

1. This is not an exhaustive list, nor is it marque specific, if in doubt use a water repellent (WD-40) and exercise common sense
2. Use cling-film and then tin foil for the alternator, alarm housing etc as the foil is easier to mould and has greater protection properties. I suggest you use a plastic bag for the induction kit and just wrap it tight over the end to stop any water ingress.
3. For the intercooler the best way to cover is to get a flat sheet of cardboard and just cut it to size so it fits and covers the fins. Cardboard will normally protect the fins for the duration of the washing. It will get soaked so discard after the wash.
4. If you are uncertain of how to proceed on something not included here; talk with somebody who has marque /model /year specific knowledge.