Most people only think about washing the painted surfaces of their vehicles, but there are great reasons to also wash your engine:

Chance of an underhood fire is reduced.

Engine runs cooler without a layer of grime.

It's easier to diagnose leaks which stand out more with clean engines.

Premature wear of components and belts may be prevented by removing dirt particles.

You'll prevent rust and corrosion.
Never wash with engine on. Do not touch moving parts. Do not spray closer than one-foot from surfaces, particularly electronics and wires.
Pull your vehicle into an Ernie's self-serve bay and turn engine off. Turn dial to ENGINE. Take spray gun and squeeze trigger for high pressure. Spray the engine thoroughly to wash away dirt.
If necessary, use a small hand-brush or towel to loosen grime. Do not use our foaming brushes which should only be used on the vehicle's exterior. You can also use a plastic scraper to scrape away stubborn deposits being careful not to damage components or wiring.
Once dirt has been loosened, change the selector to RINSE and spray the engine thoroughly. If any areas need more cleaning, repeat the process. Close hood and start engine to dry the moisture.
To make the engine compartment really shine, use Armor-All protectant on the plastic and rubber parts such as hoses, gaskets, wire coverings, shields, etc. Do not use on belts, though, because slippage may occur. Make sure engine is not running or hot for this step.
For most jobs Ernie's engine detergent will work well. If your engine has thick deposits, you may want to use an engine degreaser such as Gunk®. Ernie's wash bays are the best place to use degreasers because there will be a lot of oily drippings that can ruin a driveway.

Make it a point to wash your engine more often. The more frequently you wash your vehicle in general, the easier each job will be.