The first thing to do is make sure that your engine is cool (or at least only slightly warm). You don’t want your degreasing products to disappear before they have a chance to do what they need too.

Next, you need to cover and protect your electrics! A good way to do this is to grab roll of aluminium foil and tear up small bits as needed to cover your couplers, distribution system, etc.

Now grab some good quality degreaser. The thing to avoid is caustic or solvent-based ones. Although these can both clean very well, they’re more hazardous to use for both yourself and the environment as well as not being totally safe for the car too. Caustic and aluminium parts rarely go well together while solvents and paintwork can be bad too. Modern detergent-based formulations are really effective nowadays and with a little time to act and the occasional bit of scrubbing you should be able to deal with all the built up oil, grease and grime.

So spray your engine area and go do something else for about 10 minutes. Maybe get scrubbing on some of the problem areas. Then come back with a low-pressure hose and rinse off the degreaser. Don’t go crazy on the rinsing and don’t use a high-pressure system, there’s no real need and you just risk forcing water into those electrical bits you spent all that time protecting.

Give it a quick wipe down and then remove your bits of foil. Now you can start your engine and give it about 5-10 minutes to dry up the last of the water. Don’t leave it on longer or else you’ll need to wait even longer to do the next step.

Now grab your vinyl/rubber/trim protectant of choice. I don’t usually recommend one thing over another but if you budget allows, grab some 303 aerospace protectant. It’s magic stuff although things like armour all also do a great job for a bit less. Spray it on your hoses, plastics, rubber, shielded wires, etc. and then wipe off any and all excess. If you’re not very pleased with the results by this stage, you must’ve missed something!

So yeah, you’re pretty much done now. Check out the pic below.

GC WRX engine bay after cleaning.