Professional Engine Bay Detailing and Protection Guide

The engine must be 'warm to the touch' but never hot. If the engine is cold, run it for 2-3 minutes. If it is hot from a long drive, leave the bonnet open for at least 45 minutes. Cleaning a hot engine can cause thermal shock to the block or crack the exhaust manifold, and chemicals will flash/dry too quickly, causing permanent staining.

Identify sensitive components: the alternator, fuse box, coil packs, and the air intake. Use aluminium foil to wrap these tightly; foil is superior to plastic wrap as it stays in place and is heat resistant. If you have an aftermarket 'pod' filter, cover it completely with a heavy-duty plastic bag secured with a rubber band.

Before introducing liquids, use a vacuum or compressed air to remove loose leaves, twigs, and the 'red dust' buildup common in Australian engine bays. This prevents the dust from turning into a thick mud that can clog drainage channels or settle in the radiator fins.

Mix your APC according to the soil level. For a standard engine bay, a 1:5 (product to water) ratio is usually sufficient. For heavy oil leaks or neglected older vehicles, use 1:2. Always use a dedicated spray bottle with a high-quality foaming trigger to increase 'dwell time' on vertical surfaces.

Using a wide-angle spray pattern, lightly mist the entire engine bay from a distance of at least 50cm. The goal is to dampen the surfaces, not to flood them. Avoid direct high-pressure spray on electrical connectors or the firewall area where the ECU is often located.

Apply your diluted APC or degreaser generously, starting from the lower sections and working upwards. Ensure the underside of the bonnet is also covered if it lacks an insulation pad. Allow the product to dwell for 3-5 minutes, ensuring it does not dry out in the heat.

Use a large detailing brush to agitate the degreaser on the engine cover and plastic trim. Agitation is critical as it breaks the static bond of the dirt. Work the product into a light lather, paying attention to the texture of the plastic where dust resides.

Switch to a smaller, long-handle brush to reach between hoses, around the battery tray, and near the strut towers. These areas often collect salt and dust which can lead to localized corrosion if not thoroughly cleaned and neutralised.

If your bonnet has an insulation pad, only lightly mist it and wipe with a microfibre. For painted metal undersides, agitate with a soft brush. This area reflects heat back onto the engine; keeping it clean helps with overall thermal management.

Rinse the engine bay using low-pressure water. Start from the back and work forward. Ensure all white foamy residue is gone. Look for 'sudsing' in corners; if you see foam, keep rinsing. Residual degreaser can turn acidic and etch aluminium if left to dry.

Inspect for missed spots, particularly around the lower engine block and gearbox housing. Repeat degreasing and agitation on these stubborn areas if necessary. Australian red dust often requires a second pass to fully emulsify the iron-rich particles.

This is the most critical step. Use a leaf blower or dedicated car dryer to blast water out of spark plug wells, electrical connectors, and bolt heads. Standing water in these areas can cause misfires or 'check engine' lights once the vehicle is started.

Wipe down all accessible surfaces with a clean microfibre towel. This removes any final traces of dirt and prevents water spotting on the paintwork. Check the foil covers to ensure they haven't moved and that the components underneath are dry.

Carefully remove all aluminium foil and plastic bags. Use a dry microfibre to wipe any condensation that may have formed under the covers. Ensure no tools or towels have been left in the engine bay before proceeding to the next stage.

While the plastic and rubber are still slightly damp (or completely dry depending on product instructions), spray a water-based dressing like 303 Aerospace over the bay. This product provides essential UV protection, which is vital in Australia to prevent plastic components from becoming brittle and cracking.

After letting the dressing sit for 5-10 minutes, use a fresh microfibre to wipe off the excess. This 'levels' the product, leaving a factory-satin finish rather than a greasy, high-gloss look that would otherwise attract more dust.

Start the engine and let it idle for 5-10 minutes with the bonnet closed. The heat generated by the engine will help evaporate any remaining moisture in hard-to-reach areas and 'set' the dressing onto the rubber hoses.