What can I use to wash an engine?

[AidenLee]

You can safely and effectively wash your engine using a dedicated engine degreaser or a diluted all-purpose cleaner, paired with soft brushes for agitation and a low-pressure water source for rinsing. The core process involves protecting sensitive electronics, applying and scrubbing the cleaner, rinsing thoroughly, and drying completely. According to industry practices documented by professional detailing services and automotive publishers like Hagerty, improper cleaning is a leading cause of post-wash electrical issues, making methodical protection and product choice critical.

For degreasers, commercial products like Oil Eater, Simple Green All-Purpose Cleaner (diluted 1:10 with water), or P21S Total Auto Wash are formulated to break down grease without damaging most engine bay materials. Avoid harsh acids or alkaline household cleaners not designed for automotive use, as they can corrode aluminum and strip protective coatings. The key is allowing the degreaser to dwell for 3-5 minutes to emulsify grime but not letting it dry on the surface.

Essential tools extend beyond chemicals. You’ll need an assortment of soft-bristle brushes (including detailing brushes for tight spots) and a low-pressure water source. A standard garden hose with a spray nozzle is ideal. If using a pressure washer, maintain a distance of at least 12-18 inches and use a 25-degree or wider nozzle tip; high-pressure streams can force water into seals and connectors. For drying, a master blaster or a leaf blower is more effective and safer than towels at removing water from crevices.

Protecting electronics is non-negotiable. Before applying any product or water, cover the alternator, exposed air intake, engine control unit (ECU), and fuse boxes with plastic bags or aluminum foil. This step prevents water intrusion that can lead to costly malfunctions. Modern engine bays have more sensitive components than older models, so this precaution is universally recommended.

A systematic, step-by-step approach ensures a clean engine bay without problems. The table below outlines the critical phases:

Phase	Key Action	Product/Tool Example	Critical Note
Preparation	Engine cool-down, cover electronics	Plastic bags, foil	Engine must be cool to the touch to prevent cleaner flash-drying.
Application	Liberally spray degreaser	Oil Eater, diluted Simple Green	Apply from bottom up to minimize drips on cleaned areas.
Agitation	Scrub surfaces with brushes	Soft-bristle brush, detailing brush	Focus on textured surfaces and grease accumulations.
Rinsing	Low-pressure rinse	Garden hose, wide-pressure washer tip	Rinse thoroughly from top to bottom, removing all cleaner residue.
Drying	Remove all moisture	Air blower, microfiber towels	Compressed air or a blower is best for electrical connectors.
Finishing	Apply protectant	303 Aerospace Protectant	Dressing on plastics and rubber prevents fading and cracking.

Post-cleaning, applying a water-based protectant like 303 Aerospace Protectant to plastic and rubber components restores a dark, like-new finish and provides UV protection. This final step is not just cosmetic; it helps prevent premature aging and cracking of hoses and covers. For extremely stubborn, caked-on grease, a second, targeted application of degreaser may be necessary, but always prioritize gentle, repeated efforts over aggressive chemical or mechanical action that risks damage.

[VonAutumn]

As someone who cleans their own cars every weekend, here’s my go-to method. I swear by Simple Green. I mix it about one part cleaner to ten parts water in a spray bottle. The engine needs to be stone cold—I usually do this first thing in the morning. I wrap the alternator and battery terminals in grocery bags secured with tape. Spray everything down, let it sit for a few minutes, then gently scrub with a cheap paintbrush from the hardware store. I only use the hose on a gentle “shower” setting to rinse. Afterward, I use my leaf blower to get most of the water out of the nooks. It’s simple, cheap, and I’ve never had a check engine light come on afterward.

[Nick]

In my professional detailing shop, engine cleaning is a service we offer with zero margin for error. Our protocol is defined by safety and results. We exclusively use pH-neutral, biodegradable degreasers like P21S Total Auto Wash. The first tool we reach for is not a sprayer, but a diagnostic light to visually inspect and mentally note every wire loom and sensor location. We use professional-grade air blowers to pre-dry sensitive areas before applying any product. Agitation is done with boar’s hair detailing brushes—they are stiff enough to clean but soft enough to not scratch. The rinse is a mist, not a jet. Our final sign-off is a start-up test: the engine must idle perfectly before the car leaves the bay. This meticulous process protects our reputation and the client’s vehicle.

[LaNevaeh]

Owning a classic car makes you very cautious. Harsh chemicals are out of the question for my 50-year-old engine bay. My approach is gentle and patient. I use a mild dish soap diluted in warm water for general grime. For oil residue, I apply a small amount of citrus-based degreaser with a toothbrush, then wipe it off immediately with a damp cloth—no soaking. I avoid spraying water directly; instead, I use a bucket of clean water and microfiber towels to wipe sections clean. Drying is a slow, thorough process with a soft towel and time. The goal isn’t sterile perfection, but a respectful, damage-free clean that preserves all the original fittings and patina. Preservation always trives over aggression.

[VonRyder]

If you’re looking for the most straightforward, no-fuss method, here it is. Buy a dedicated engine degreaser from an auto parts store. Ensure your engine is cool. Cover the alternator, any open filters, and the fuse box with plastic bags. Spray the degreaser everywhere, wait five minutes, and gently scrub thick gunk with a brush. Rinse using a garden hose on a light spray setting—do not use a pressure washer’s concentrated stream. Start the engine and let it idle for 10-15 minutes. The heat will evaporate the remaining moisture from most areas. This basic method removes 90% of dirt and improves appearance significantly with minimal risk. It’s a practical maintenance clean, not a concours-level detail, and it works for most modern vehicles when done carefully.