Engine baysDoor jambsUndercarriageTrim

01 — Know what you are cleaning and what to protect

These areas are not one job. They are four, and each has its own risks. An engine bay has heat, electronics and rubber hoses. Door jambs have latches, wiring grommets and paint edges. The underbody and wheel wells face salt, mud and brake dust. Emblems and trim have adhesives and soft finishes that harsh products can stain or lift.

Before starting, read the owner's manual for any warning about washing the engine bay, and look at the vehicle. Note where the battery, fuse boxes, air intake, alternator and exposed connectors are. Work on a cool or only slightly warm surface, in the shade, and test every cleaner on a small hidden spot first. Plan to work from the dirtiest and lowest areas last, so grime from the underbody never gets carried onto clean parts.

02 — Engine bay: prepare before any water

The engine bay should be cool to the touch, or at most slightly warm. Cold water on hot metal is hard on parts, and a hot surface dries cleaners before they can work.

Start with the dry work:

• Remove leaves, pine needles and loose debris by hand, with a soft brush or with low-pressure air.

• Check that the battery terminals are secure, and remove the key from the ignition.

• Cover the air intake opening, exposed alternator, fuse box, and any open connector with plastic bags and painter's tape.

• Check whether the vehicle maker or an engine-bay cover calls for any other protection.

On newer vehicles with a lot of exposed electronics, many detailers skip the rinse and use a wipe-down method instead: spray diluted cleaner on a towel or brush and wipe, working in small sections. It is slower, but it keeps water out of places it should not go.

03 — Engine bay: degrease, agitate and rinse gently

Pick a cleaner for the level of grease. Purple Monster is a medium-duty all-purpose cleaner and degreaser that its label directs you to dilute 4:1 with water for general degreasing, with full strength reserved for heavily soiled spots. Orange Crush CarCandy is a water-based, biodegradable citrus all-purpose cleaner, and its label directs you to dilute it 4:1 with water for engine degreasing and apply it with a sprayer. Follow the label on whichever product is used, and never mix cleaners together.

Apply the diluted cleaner to a small section at a time. A foam gun such as the Tornador Foam Gun helps because the foam clings to vertical surfaces instead of running off, and the product list for the gun places it with engine bay work. For spot work, a chemical-resistant spray trigger holds up better to strong cleaners than a standard trigger.

Agitate with soft brushes. A boar hair set such as the MaxShine 3pc Detailing Brush Set comes in three sizes, which suits the mix of flat covers, tight corners and hose clamps in a bay. The Narrow Seam Detail Brush reaches along edges and between components.

Never let the cleaner dry on the surface. If it starts to look tacky, wet it again or rinse. Rinse with a gentle stream of water at low pressure, aimed away from covered parts and electrical connections, or use damp towels. Skip a high-pressure jet near connectors, seals and sensors.

04 — Engine bay: dry and dress

Remove the coverings, then dry the bay. Use low-pressure air if available, plus clean microfiber for the surfaces you can reach. Open the hood and let it sit in the open air for a while. Starting the engine and letting it idle for a few minutes helps dry hidden areas, but only once nothing is left pooled around connectors.

A dressing is optional. If you use one, pick something made for the job. Non-Silicone Instant Shine is described as a body-shop-safe finish product with no silicone, made for rubber, plastic and vinyl, and for hard-to-reach areas. The T&T Tire & Trim Restorer label lists engine bay components among the surfaces it is safe on, and says to clean the surface with an all-purpose cleaner first. Apply sparingly, wipe off the excess, and keep dressing off belts, pulleys, brake fluid reservoirs, and any other part that needs grip or must stay dry.

05 — Door jambs and sills

Door jambs collect grease from hinges, wax residue and road film, and they show every time a door is opened. They are also where a careless spray can reach a latch, a speaker or a wiring grommet.

Work with the door open and the area in shade. Apply a diluted all-purpose cleaner to a brush or towel rather than spraying the jamb directly, and keep the product away from the latch mechanism, door-lock actuators and any exposed wiring. Clean the painted jamb, the sill, and the rubber door seals separately, using a fresh towel for each so grease from the hinges does not get smeared over the seal.

For seams, hinge pockets and around the latch, use a thin brush or swab. The Narrow Seam Detail Brush has a long angled head that reaches tight seams, and Cotton Detailing Stix have a fine point at one end and a flat tip at the other for crevices. Wipe each section dry with clean microfiber, such as 350GSM Edgeless towels, which are tag-free and low pile. Keep dressings off the sill area where people step, because a slippery surface is a hazard.

06 — Undercarriage and wheel wells

The underbody is the one place where heavy rinsing is useful, because the goal is to remove salt, mud and packed dirt. It is also the area where the work can be dangerous.

Never work under a vehicle held up by a jack alone. Use rated jack stands or ramps on level ground, or do the cleaning from outside using long-handled tools. Rinse the wheel wells and underbody from the outside edge in, working steadily so that loose dirt flows out and down. In winter conditions, rinse more often, because salt left on the underbody keeps working on metal and fasteners.

For stuck grime in wheel wells, spray a diluted all-purpose cleaner and agitate with a brush that has soft flagged bristles. The Long Handle Soft Wheel & Grille Brush is 20 inches long with an angled head and bristles listed as resistant to acids and detergents, which helps with reach and with chemical contact. Rinse thoroughly.

Keep cleaners and dressings away from brake rotors, pads and calipers, since anything that gets on a friction surface can reduce braking performance. If a cleaner does reach the brakes, rinse it off completely and check the pedal feel at low speed before driving normally. Skip dressings on wheel well liners unless the product label says it is suitable.

07 — Emblems, badges and trim

Emblems and badges collect wax, polish and compound residue in their edges, where a towel cannot reach. Heavy scrubbing, aggressive solvents or stiff bristles can lift the edge of an emblem or scratch its finish.

Use a soft brush with a gentle cleaner to loosen the buildup, then remove it with a swab. Cotton Detailing Stix are 100 percent cotton swabs, and the pack notes they remove wax, compound and polish residue from emblems and side molding. For larger flat areas, the Detail Stix Starter Pack uses a rigid core with removable microfiber and brush covers, which gives the control of a swab with more cleaning surface. Use light pressure and change the swab or cover as it gets dirty.

For genuine chrome trim, Bling Bling Chrome Polish from Car Candy is made for chrome surfaces. Test it on a hidden spot first and keep it off painted, plastic and chrome-look finishes unless the label says otherwise.

08 — Restore and protect exterior trim

Faded black trim is one of the first things that makes a vehicle look old. Always clean first, since dressings and coatings do not bond well to a dirty surface. Use a diluted all-purpose cleaner and a soft brush, rinse, and let the trim dry fully.

There are three common routes, depending on how faded the trim is and how long it should last:

• Dress it. Non-Silicone Instant Shine gives a gloss finish and can be applied by spray and buffed, or left to dry.

• Restore and protect it. The T&T Tire & Trim Restorer is a ceramic trim and tire dressing, and its label describes safe use on all exterior plastics and rubber, with a deep black finish and no greasy residue or sling.

• Coat it. CandyCoat Trim is a professional-level ceramic coating for exterior trim, with UV protection listed as lasting up to three years. The label says to apply it only to outside trim, out of direct sunlight, on a clean dry surface prepped with a solvent or a 70/30 isopropyl alcohol mix.

For trim that is badly faded or worn, Black Fuzion is a black dye made to revive faded plastic trim. Mask nearby paint with tape before using any dye or coating, and apply with a small applicator such as the Tire Saver 4pk, which is sized for tight trim areas.