Pressure Washing Your Engine Bay? Why Mechanics Say It’s a Terrible Idea

You’ve seen the satisfying videos—high-pressure water blasting away years of grime from a dirty engine bay, leaving it looking brand new. It’s tempting to grab your pressure washer and do the same. But before you spray, here’s what every mechanic wants you to know: Pressure washing your engine can cause thousands in damage.

Why Pressure Washing Your Engine Is a Bad Idea

1. Water Forces Its Way Into Sensitive Electronics

Your engine bay is packed with:

• Wiring harnesses (water causes corrosion & short circuits)
• Fuse boxes & relays (moisture leads to electrical failures)
• Sensors (O2, MAF, crank position) (water intrusion = check engine lights)

Mechanic’s warning: “I’ve seen cars towed in after a DIY engine wash because the ECU got fried. A $10 $carwashturnedintoa$1,200 repair.”

2. It Can Destroy Bearings & Seals

High-pressure water can:

• Force water past seals into alternators, starters, and turbochargers
• Wash away grease from pulleys and bearings, leading to premature wear
• Cause belt slippage by soaking serpentine belts

3. It Can Hydrolock Your Engine (Yes, Really)

If water gets sucked into the air intake, it can:

• Bend pistons (water doesn’t compress like air)
• Destroy the engine (requiring a full rebuild)

Real-life example: “A customer pressure-washed their engine, water got into the intake, and the engine seized. Total loss.”

The Safe Way to Clean Your Engine Bay

If you must clean under the hood, follow this mechanic-approved method:

What You’ll Need:

• Degreaser (Simple Green, Purple Power, or dedicated engine cleaner)
• Soft-bristle brush (no wire brushes!)
• Microfiber towels
• Compressed air (or a leaf blower)
• Plastic bags (to cover sensitive parts)

Step-by-Step Safe Cleaning:

1. Cool Down the Engine – Never clean a hot engine (thermal shock can crack components).
2. Cover Electronics – Bag the alternator, fuse box, and intake.
3. Spray Degreaser – Let it sit 5-10 minutes (don’t let it dry).
4. Gently Scrub – Use a soft brush on tough spots.
5. Rinse with Low Pressure – A garden hose on “shower” mode is safe.
6. Blow Dry – Use compressed air to remove standing water.
7. Start the Engine – Let it idle to evaporate leftover moisture.

When to Never Wash Your Engine

• After driving (hot parts + water = damage)
• If you have electrical issues (moisture makes them worse)
• Before an inspection (wet sensors can trigger false codes)

The Bottom Line

Pressure washing might look effective, but the risks far outweigh the rewards. A simple degreaser and gentle rinse is all your engine needs.

Still Worried About Grime?

Leave it to the pros—many detailers offer engine bay cleaning for under $50 (way cheaper than a new ECU).