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topic 5333

Anodizing Cast Aluminum for Under-Hood Engine Parts


Q. I came across this website doing a search on Anodizing. Very Impressive I must say, but still at a loss for what I'm looking for. Just about all the technical information on here is way over my head, definitely not my field.

From what I understand: Aluminum can be anodized but not Cast aluminum and get the same quality as the before mentioned.

My application is for automotive use and there are a few pieces that I need to get plated, ceramic coated or something other than spray paint. I am looking for a finish that's just about identical to the "purple" Maglite flashlights, and be able to withstand normal operating temperatures associated with car engines.

Any leads would be greatly appreciated. Please feel free to contact me either by phone or e-mail.

All I'm looking for is to get some custom work done for my engine rebuild the way I want it to look, and I know there is a way just having trouble finding the right path you might say. Thank you,

- Atlanta, Georgia


A. You are very probably looking for "two step anodizing". I doubt if regular dyed anodizing will have the fade resistance you are looking for. Find a job shop that does that type of work. There are not many, but there are several. Cost is a fair bit higher. Wrought alloy anodizes beautifully, extrusions are from good to bad and castings are from fair to very bad.

James Watts
- Navarre, Florida


A. Powder coating may be an option. If the parts can be brought to a high luster, the powder coat can be applied with a translucent effect that is very attractive and this can be done in a large variety of colors.

Bill Miller
- Shinnston, West Virginia

February 2012

A. Hi, Craig and readers.

The internet is a gigantic one-room schoolhouse; so sometimes it's hard to find the information you're looking for at the level you wish. But here's a quick explanation about why it's hard to anodize certain types of aluminum: only the aluminum per se can be anodized, not the other stuff that may be in an alloy or casting like the silicon, copper, zinc, etc.

Some grades of aluminum (and all castings) have a lot of that other stuff. That other stuff doesn't etch away easily, doesn't get converted to glassy looking aluminum oxide, but just turns into a gray to black smut which may be porous or speckled, won't be bright or smooth, and won't dye to the colors you'd like. So the more of that other stuff, the less satisfactory the anodizing.

The next point, that James Watts mentioned, is that even if you do dye it, most dyes are organic and subject to degradation from high heat. So you probably need a special inorganic dye for an under-hood application. Those inorganic dyes, which are also used for architectural anodizing are applied by methods called "integral color anodizing" or "two step anodizing" but tend to be champagne to bronze to brown in color. Purple sounds unlikely for an inorganic dye; before the days of synthetic inorganic dyes, purple was so rare and difficult that it was reserved for royalty :-)

So, an attractive "purple mag lite" anodized finish for an under-hood application on cast aluminum doesn't sound very do-able to me, and would be a development project rather than something a consumer purchases. I think a powder coating or a ceramic sounds like a more promising approach. Good luck.


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

Plating or anodizing a Webasto aluminum heater

October 31, 2015

Q. I have my hands on a Webasto thermo engine heater, it's basically a mini buddy heater that uses diesel fuel to heat up an all aluminum body heat exchanger. On the other end of the heat exchanger the vehicles coolant passes through and is pumped throughout the engine. I had the unit sand blasted to bare metal to remove all built up dirt and soot. What I'm wondering is, what would be the best suitable method of ensuring it doesn't build up particulate as easily. I was suggested to have it anodized or plated, bear in mind it will see temperatures upwards of 200 °F, with contact with diesel fuel and engine coolant. Any advice is much appreciated.

Sam Boyce
- Winnipeg, Manitoba, Canada

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