The Professional Guide to Engine Degreasing and Bay Detailing

Never degrease a hot engine. In Australian summer, engine block temperatures can exceed 90°C. Applying cold degreaser to a hot block can cause thermal shock, potentially cracking manifolds or warping components. The engine should be 'warm to the touch' (approx. 30-40°C). This warmth helps soften grease without causing the degreaser to flash-dry instantly on the surface.

Before introducing liquids, use a vacuum or leaf blower to remove loose leaves, twigs, and dead insects from the cowl and corners of the bay. In Australia, this is also a critical safety step to check for nesting spiders (like Redbacks) or rodents that may have taken up residence in the warmth of the bay.

Identify and cover vulnerable areas. Use aluminium foil or plastic wrap to tightly cover the alternator, the air intake opening (if exposed), the battery terminals, and any exposed aftermarket alarm sirens or HID ballasts. Foil is superior as it holds its shape and provides a better seal against high-pressure mist.

Mix your degreaser according to the level of soil. For a standard detail, a 4:1 (Water:Product) ratio is usually sufficient. For heavy 4x4 red dust and oil caking, use a 1:1 ratio. Test a small, inconspicuous area of plastic trim to ensure the chemical doesn't cause staining or 'whitening' of the finish.

Starting from the bottom and working upwards, spray the diluted degreaser liberally across the engine bay. Focus heavily on the lower block and firewall where oil tends to accumulate. By working bottom-to-top, you prevent clean streaks from forming on the lower sections as the chemical runs down. Ensure the underside of the bonnet (hood) is also sprayed if it lacks an insulation pad.

Allow the product to dwell for 3 to 5 minutes. Do not allow it to dry. In 35°C+ weather, you may need to mist the area with a light spray of water to keep the degreaser active. You will see the grease begin to emulsify, changing from a dark solid to a milky brown liquid. This is the chemical breaking the molecular bond between the oil and the metal.

Use your stiff-bristled brush to scrub the metal surfaces, such as the valve cover, intake manifold, and strut towers. Use the soft-bristled brush for plastic covers and rubber hoses. Agitation is key; the chemical loosens the dirt, but the mechanical action of the brush ensures it is fully suspended in the solution for rinsing.

Using a pressure washer from at least 50cm away, or a garden hose on a 'shower' setting, rinse the engine bay. Always keep the nozzle moving—never dwell on a single electrical connector. Focus on flushing the degreaser out of 'pockets' like spark plug wells and battery trays where caustic chemicals can sit and cause long-term damage.

Inspect the bay for missed spots, particularly around the oil filter housing and lower subframe. Often, the first pass reveals hidden layers of grime. Re-apply degreaser to these specific areas, agitate, and rinse again. A truly professional result often requires two lighter passes rather than one aggressive, high-concentration chemical blast.

Rinse the underside of the bonnet carefully. If you have a fabric heat shield, avoid high pressure as it can fray or delaminate the material. Use a damp microfibre cloth to wipe the edges and the latch mechanism, which is often a forgotten grease trap that can soil your clothes during future maintenance.

This is the most critical step for modern cars. Use compressed air or a high-powered leaf blower to blast water out of every electrical plug, the alternator housing, and around the ignition coils. Pay special attention to the 'valleys' of the engine where water pools. Removing this water prevents electrical shorts and unsightly water spotting.

Use your utility microfibre towels to hand-dry the remaining surfaces. This manual contact allows you to feel if any grit or grease remains. Wipe down the tops of the radiator, the battery, and the inner guards. Remove all foil/plastic covers from the components you protected in the preparation phase.

Start the engine and let it idle for 5 to 10 minutes. The heat generated by the engine will evaporate any residual moisture in hard-to-reach areas. While the engine is running, listen for any unusual sounds or check for warning lights on the dashboard, which would indicate water ingress into a sensor.

Once the engine is dry and slightly warm, apply a water-based dressing to all plastic and rubber components. Avoid 'glossy' silicone products as they attract the fine Australian red dust. A matte or satin finish dressing will protect the rubber from UV cracking and make future cleaning significantly easier as dirt cannot bond to the treated surface.