Best way to clean an engine bay?

[ENV²]

Go lol

[Ynnekdude]

Because of coilpack issues, I am really hesitant to ever have a water stream directly touch my engine bay. Generally, I get a towel damp with Adam's APC and then rub everything down. Then I just grab a damp water rag and wipe everything down again. Afterwards things get dressed. It never looks as good as new but I am too scared to ever really get the engine bay wet.

[TOGWT]

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

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.

[TOGWT]

1. Warm up the engine
2. Cover water sensitive components
3. Apply a mild degreaser and agitate
4. Rinse away residue
5. Remove any applied component protection (cling film, foil, etc)
6. Apply protection to rubber / vinyl parts
7. Start and allow engine to warm up and dry engine bay

[Crucible35]

I think many are in the same boat when I say that I would love to be able to clean the engine, but if I opened my hood and someone asked me to point out the coil packs, the alarm housing or even the ECU I wouldn't have a clue what they look like. Sure, I could do some research to identify each component, but even then I think I would need a labeled diagram of our engine bay to clarify what would actually need to be covered.

[TOGWT]

If it has electrical wires going to or from it or it has an open end; cover it

Other than that-take it to a professional and have him/her do it for you

[Crucible35]

That's what I was thinking too.....although I had the dealership do the engine bay a couple of years ago and.....two sets of coil packs later, got my car back. The other day I was in at a different dealership and asked them....they said they wouldn't do it, or at least my SA wouldn't recommend it.

[Leor604]

I've always washed my engines as follows:

Get engine warm (not HOT)
Wet down with low pressure water. I use the "shower" setting on the nozzle.
Spray with mild detergent solution (dawn, simple green, car wash soap). I never use a harsh degreaser.
Agitate with long bristle brush
Rinse using "shower" setting.
Go for a drive to fully warm and dry out engine bay.
Once cool, you can detail the plastics and hoses if you want your engine to be in "show" condition. I just want it clean so typically don't do this step.

Never had an issue with not starting or any electrical gremlins. YMMV.