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I just cleaned much of my engine compartment with Abro Heavy Duty Degreaser, and I noticed that on certain metal parts like the valve cover, thermostat housing and transmission housing a white powder has formed:

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I left the degreaser on for maybe 30 seconds to a minute, and in some cases agitated it with a brush, then pretty thouroghly rinsed it with a water hose.

This powder won't blow off, but it rubs off pretty easily with my finger as can be seen in the picture. This did not occur with other metal parts such as the engine block, and various metal pipes and connectors, nor did it happen on hoses or painted parts. I think the parts it did happen on may all be made of aluminum.

  1. Why did this happen?
  2. How can I easily clean this?
  3. How can I prevent this from happening in the future when I clean?
Robert S. Barnes
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2 Answers2

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Believe it or not, that is corrosion. You are correct in your assumption that the Valve Cover is certainly cast aluminum. Aluminum can be damaged by many de-greasers that are too aggressive. This happens due to a chemical reaction by the cleaner with aluminum parts. Steel or painted parts will not have this oxidation occur. Usually you can avoid this by thoroughly rising or washing the parts provided that the cleaner is not so aggressive that it is etching the parts.

Most notably, oven cleaners/degreasers contain Sodium Hydroxide which actively eats aluminum surfaces unless deactivated relatively quickly by a thorough washing or rinsing.

Failure to do so results in this oxidation occurring once it dries.

The best way to clean this is with a light dishwashing detergent and a stiff nylon bristle brush. More stubborn areas may need a more aggressive cleaner, however since you mentioned it comes off with a touch, it's likely easily removed with just some mild agitation and elbow grease.

Preventing it from happening going forward, avoid using harsh chemicals on your Aluminum. Find Aluminum safe degreasers, or just thoroughly rinse them before they dry out. Never bake out degreaser on aluminum parts. Many degreasers instruct you to work on a warm motor, this is fine for steel parts, but with Aluminum, you should only clean it when it's cool and make sure to rinse it thoroughly.

Jeep Cherokee Rescue Society
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Just had this happen to me. Degreaser still messes up powercoating. Just don't use degreaser in my opinion.

Davidson
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