I've been washing the engine bays of all of the cars I have driven for the past 25 years or so.
How did I get started? Isn’t this really bad for my car? Why did / do I bother?
I worked with a guy back then who was seriously obsessed with keeping his 1986 Thunderbird clean - way more so than I ever was or currently am. He popped the hood one day and I marveled at the near showroom appearance of the ~ 4 year old engine bay.
I asked the same questions many of you have about getting the various components and systems wet. The owner of the car was quite talented with most things automotive, especially the electrical systems as he was a professional car audio install technician with a high end audio shop. The sound system in that car was phenomenal even by today’s standards.
He was quite confident that the water would not cause problems. That engine bay got a rinse with nearly every car wash and a regular washing. I was still skeptical. I carefully tried it myself starting out away from wiring and the alternator gradually becoming more confident until the entire engine bay was squeaky clean. It looked great then and still does.
I’ve never had a problem with getting any electrical items wet – even a distributor. A modern engine bay is engineered to get somewhat wet during normal use. Assuming your engine bay is in reasonably good shape, with no defects in the electrical, crankcase ventilation and intake systems you will most likely have no problems as well. This works best and is easiest from when a car is new as dirt and oxidation never have a chance to start. Even an older engine bay can be transformed with a little extra work.
This is being provided as a guide only - I cannot guarantee you will not experience difficulties.
Wash your engine bay at your own risk.
This is what works very well for me …
Start with a cold engine. A warm or hot engine will cause any detergent you spray on to quickly evaporate. Letting it sit and soak is what gets things clean. I’ve never covered electrical components, but have put a plastic bag over open exposed conical air filters. Obviously do not spray liquid directly into the air intake. Use a garden hose with a variable nozzle to go from a fine spray to a concentrated stream depending on what you are hosing down. A pistol grip style of nozzle is the easiest and fastest to use. A high pressure car wash hose is asking for trouble. Common sense is called for here.
This the perfect nozzle imo. Plastic coated so it is easier to use in cold weather and has a rubber collar around the outlet to prevent damage if it makes contact with the paint. I just bought this to replace my worn out old one.
I wash the underside of the hood first. I removed the fiber insulation the day I brought the WRX home as I have with all of my previous cars. I personally believe the insulation is largely for sound suppression. It becomes a dirt magnet if left on and seems logical to assume it also promotes heat soak. I have not observed any engine heat related effects on the exterior hood paint with four different cars.
Hose down the hood, fenders, windshield and engine hosing off loose debris. Spray liberal amounts of full strength Simple Green all over, especially in the inaccessible areas. You would probably see good results with diluted Simple Green as well. I use a quart sized commercial type variable nozzle spray bottle rather than one Simple Green is sold in – it’s much easier and faster. Hose off any overspray from the fenders as Simple Green is too harsh for polished waxed surfaces. Let soak for ~5 minutes or so. While I wait I have a few odd brushes I use to scrub around where I can.
Thoroughly hose off all areas (with common sense) until all traces of the detergent are gone. Some areas can take higher pressure, like the intercooler and around the firewall. Once the car / engine wash has been completed I take the car on a drive to heat and dry the engine bay out. I repeat this maybe four times a year – that’s all it takes to keep everything looking showroom clean. The WRX’s under engine cover does a great job in keeping dirt out of the engine bay. My previous cars without a bottom cover required more frequent washing to keep things as clean.
Happy bay cleaning.