I've got an all-aluminium subaru ej205 block that I'd like to clean before I rebuild it. I've bought a metal bin large enough for the engine halves and I'm looking at a degreaser such as this one: https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F182187203185 Most of the degreasers I've seen mention to be cautious with aluminium parts. I've only experienced them etch polished aluminium, but I only used it for 10'-20' so far. - what is the overall "safe" time frame to dip a block into the degreaser? - is there any advantage if I boil or heat up the solution whilst the block is submerged into it? - short of soda blasting it, what are other safe methods to clean blocks and cylinder heads? Acidic or Caustic?

Please bear in mind the cylinder will be bored and the decks will be skimmed afterwards.

Many thanks of anyone who can help!

  • Not sure I'd use that as it states while it can be used to clean aluminum, it'll hurt it if left on it too long. I wouldn't use anything which has the potential to hurt your block. Mar 24, 2019 at 15:28
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    @Aethenosity - Wow, do I have a bad habit of doing that! :o) Updated and thanks. Mar 24, 2019 at 16:24

2 Answers 2


Get a degreaser that will only affect grease - then you won't have to worry about the aluminium.

If they do warn about possible effects, then increasing the temperature and/or time will increase the chances of damage.

Do note that damage may occur where it is not visible, like inside oilways... If an oilway wall gets corroded so it is too thin - the eventual failure could seize the engine...

I took my bare blocks (aluminium) to an engine rebuild shop and they used their parts cleaning machine for a small fee - perfectly clean...

  • Yes, a parts washer versus a hot tank for aluminum. Non-caustic and will definitely get it clean .. as long as they use good cleaning solvent in their machine :o) Mar 24, 2019 at 15:09
  • @Pᴀᴜʟsᴛᴇʀ2 I came across a cleaning chemical that was used in the paper mill - cleaned dirty engines a treat - but if split neat on aluminium you could see the metal dissolving and it stung like crazy if you got it on your skin - probably no longer available due the Health abd Safety Wizards...
    – Solar Mike
    Mar 24, 2019 at 15:12
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    @SolarMike probably sodium hydroxide (AKA caustic soda, lye). Once it gets through the natural oxide layer on Al the reaction is fairly quick and gives off hydrogen. And it's used in the paper industry, an effective degreaser, and unpleasant on skin.
    – Chris H
    Mar 24, 2019 at 15:43
  • as @Paulster2 has recommended having it done in a engine has several advantages. They will be very familiar with the products they use, they know how to dispose of the gunk when they are done.
    – mikes
    Mar 24, 2019 at 16:35
  • @ChrisH Sodium hydroxide works fine for unblocking drains but even then it comes with a warning not to use it on metal plumbing. It was hard to beat "genklene" (trichloroethane) before it was banned because of greenhouse gas emission regulations.
    – alephzero
    Mar 24, 2019 at 16:50

I had a Porsche engine case halves and transmission case vapor degreased by a shop run by an ex-factory mechanic years ago. He used trichlorethane, which has been replaced by trichlorethylene, N-propyl bromide or whatever for vapor degreasers. For cleaning before adhesive bonding, one "standard" combo is isopropyl alcohol and hexane, 50/50, IPA removes polar comtaminants (dirt), hexane, non-polar ones (grease/oil.) Paint thinner alone or followed by IPA is good enough. One of the best degreasers I've used is Dawn diswashing detergent, cleans well, isn't metal aggressive. Could be used after a solvent.

When I worked for an aircraft engine company, the last thing they did after testing before wrapping and shipping an engine was to spray the entire outside with trichlor out of a huge pressure washer. Worked spectacularly well, removed dirt and oils/grease. Had to be done outside with respirators. An environmental disaster and not done today.

Kind of depends on what you're trying to achieve. If you want factory clean and factory appearance, easiest route and best results would be to take your parts to a transmission or engine shop for vapor degreasing. Alkaline cleaners, detergents, soaps, etc can clean well but won't result in the same shiny new surface; they'll corrode the aluminum surface leaving a white or black residue which probably won't hurt the metal without long exposure to the cleaner or even be noticeable except compared to vapor degreased part.

Vapor degreasing dips parts in hot solvents between exposures to solvent vapors. Only consideration is making sure oil passages, etc are positioned so the liquid phase can run out; it's simple. Any other method may require small long brushes to clean passages depending on how clean you want to be. The heads will definitely need to scrubbed. If you use an alkaline/detergent cleaner be sure to do a very thorough final rinse ideally in distilled or RO water unless your tap water is below pH 7.

What's your tank made from? Polyethylene, or stainless steel, I hope. Aluminum and steel make a great battery, with AL as the anode, the terminal that corrodes. BTW, Drano is a mix of NaOH and aluminum chips. Makes a lot of gas when exposed to water, the chips churn at the clog until they corrode away in a few minutes; meaning alkaline chemicals, if aggressive enough, will eat AL rather quickly under the right conditions.

Whatever you choose, if not vapor degreasing, the important things are to limit exposure to the cleaner and rinse thoroughly with neutral water. Soaking your parts for hours or days in a cleaning bath without doing a test run first isn't a good idea. The greasy areas will come clean last, the clean areas will be corroded first. Heat and agitation will increase the cleaning rate.

Really not that touchy as long you watch what's happening while cleaning. Go for functional clean vs. beautiful clean.

  • Thanks for the reply! Unfortunately I don't have access to any of those chemicals as they are all controlled under UK law. I think I'll try degreasing it with pressurised white spirit and then try a mild acid bath.If it is still in a bad condition, I send it for blasting. I'm not going after a factory look or a showroom look all I want is to clean it, recondition it and rebuild it for racing.
    – Ælex
    Mar 25, 2019 at 16:22
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    Be sure to tape off any machined surfaces before blasting, some of them cannot be re-machined.
    – Moab
    Mar 26, 2019 at 21:08

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