Engine bay cleaning - Solution of DAWN disk soap and water in a spray bottle + a variety of different sized paint brushes. For oxidized aluminum - small brass wire brushes. Rinse with a garden hose on low pressure/volume and blow-dry with compressed air, leaf blower, or reversed shop-vac.
Excerpted from the Simple Green web site FAQ ...
Aluminum — Is it safe to use Simple Green All-Purpose Cleaner on aluminum?
When used with caution and according to the instructions, Simple Green All-Purpose Cleaner has been safely and successfully used to clean aluminum. Simple Green All-Purpose Cleaner, Crystal Simple Green Industrial Cleaner & Degreaser, and Simple Green Pressure Washer Concentrates have been used on aircraft, automotive, industrial and consumer aluminum items for over 20 years. However, caution and common sense must be used: aluminum is a soft metal that easily corrodes with unprotected exposure to water. The aqueous-base and alkalinity of Simple Green All-Purpose Cleaner can accelerate the corrosion process. Therefore, contact times for unprotected or unpainted aluminum surfaces should be kept as brief as the job will allow - never for more than 10 minutes. Large cleaning jobs should be conducted in smaller-area stages to achieve lower contact time. Rinsing after cleaning should always be extremely thorough - paying special attention to flush out cracks and crevices to remove all Simple Green product
residues.
Unfinished, uncoated or unpainted aluminum cleaned with Simple Green products should receive some sort of protectant after cleaning to prevent oxidation.
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