Cleaning engine block

Discussion in 'Workshop Forum' started by andreav, May 7, 2019.

  1. andreav

    andreav True Classic

    Can you share opinions on how to clean engine block, water passages, I tried several times with blasting but require little preparation of prtoection all things where can go wrong... and once tried with sulfuric acid but again not ideal thing, messy and smells bad.
  2. NM850

    NM850 True Classic

    Albuquerque NM
    I take it to a machine shop to have hot tank dipped.
  3. fiatfactory

    fiatfactory Steve Cecchele

    Western Australia
    Andrea, google "Molasses rust removal"

    if you get a big 40 litre plastic tub with a snap on type lid, big enough to fit a whole engine block into... go to a local horse or livestock feed store and buy about 4 litres of molasses, it's the cheapest place to buy it. pour 4 litres of molasses into the tub and then mostly fill the tub the rest of the way with hot water. (ratio of roughly 10:1) and then put the rusty (I like to call it "seasoned") engine block into the tub and lock on the lid... leave it for maybe a couple of weeks.

    It's going to eat the aux shaft bearings... but it will clean the block down to virgin cast.

    It's quite a clever chemical reaction that takes place at a molecular level...

    aarpcard and Frank L. Di Gioia like this.
  4. ianlawson

    ianlawson ian - NZ

    Heh, that's a neat "diplomatic" description, Steve!! ;)

    cheers, IanL - NZ
  5. andreav

    andreav True Classic

    Thank you guys on advices, but I think I will have problem over here to find shop who have hot tank for dipping, what I m sure is pretty good way for cleaning and/or molasses. Ok, some similar acids probably can be find, I will this days check what is available and will inform you here with progress, maybe good infos for someone will be....
  6. Ulix

    Ulix True Classic

    Stuttgart, Germany
    I used phosphoric acid in the cooling passages to remove rust. Bought through Amazon.
    I had the engine on an engine stand and filled it with diluted acid.
    After a while I rotated the engine and drained the acid in large pan, then flushed the block with water.
    (Edit: I also flushed it with baking soda solution to neutralize the acid)
    Not so messy.
    I you do this on a regular basis, you could immerse the whole block in a large tub of that stuff.
    Last edited: May 13, 2019
  7. Kevin B (Asheville NC)

    Kevin B (Asheville NC) Administrator Moderator

    Asheville, NC
    Is goal to get block clean, or internals clean? For internal passages, go with what Ulix recommends. For outside of block, siple green or purple power and a pressure washer witll strip the paint and grease stains off the block to ready it for repainting.
  8. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Philadelphia, PA
    This product is meant to be used with the engine in the car and the cooling system operational:

    They have international distributors, the ones in Austria and Switzerland would be closest to you:
  9. Daniel Forest

    Daniel Forest True Classic


    Any experience with the product or just a "Google" search...?
    Dan Sarandrea (Phila) likes this.
  10. andreav

    andreav True Classic

    Important is internal cleaning of water section, engine block is now cleaned from outside and inside fully, which is not problem.

    Thank you Dan on this, but problem is that engine is fully disassembled.
  11. Dan Sarandrea (Phila)

    Dan Sarandrea (Phila) Waitin' On Parts...

    Philadelphia, PA
    Yes, I used it on my X. It performed exactly as described, in that the instructions say that the coolant will pretty much turn black which is supposed to be an indicator of it doing what it is supposed to do, which is to pull any iron oxide out of the inner surface of the cooling system. Now whether it made the cooling system better, worse, or what, I don't know :)
    Daniel Forest likes this.
  12. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Oxalic acid has been a principle cooling system cleaner for decades. You can get it in powder form and mix with water to fill the cooling passages in the block. Removes rust, scale, etc., but it isn't particularly effective for removing oil residue (if your cooling system was contaminated with oil from a blown head gasket).
  13. andreav

    andreav True Classic

    Jeff thank you on info, I have search Ebay UK and it is possible to order, can you give some tips in mixing ration or how to made right work?
  14. bpimm

    bpimm Brian Pimm

    Washougal, WA
    Oxalic acid has many uses, I have a tub of it left over from bleaching the logs in my house before finishing them, The mix ratio would be good to know.
    Be careful with it it's quite toxic.

    Also oxalic acid is not safe for Aluminum.
    Last edited: May 11, 2019
  15. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    I have some additional info on using Oxalic acid for cooling systems, including the mix ratio. I will have to dig it out and get back to you. Please remind me if I don't respond within a day or two...I've been out of town and now I'm trying to get everything caught up around here.
  16. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Regarding Oxalic acid for cleaning a cooling system.

    Cooling systems can become contaminated with many substances. The most common is rust and water deposits (minerals). But it can also happen due to oil, chemicals from other products (Dexcool was a classic example), silicate drop out, aluminum oxide, electrolysis from other metals, etc. Each type of contamination will require a cleaning process that is effective on the particular type of build up being removed. Some products are very effective on only one specific type of contaminant, while others work on many forms of contamination but at a slower/less effective rate. A balance between effectiveness and protection of the underlying materials is also needed.

    In the past there were some very effective cooling system flush products available that really worked well for most problems. Typically the better ones came in a two part container; each was a powder that you dissolved in water, one was the cleaner, the other was the neutralizer to use after the cleaner. The cleaning portion was oxalic acid. Several automotive manufacturers offered these as their own brand products, recommended to use as the cooling system flush on their vehicles (for example General Motors part #88861344). Unfortunately those products are no longer available due to EPA regulations (EPA is a government agency here that focuses on environmental issues), over how the products were disposed of. These were intended for the entire cooling system and therefore needed to be safe for all of its components (different metals, etc). So it is a good overall general cooling system cleaner.

    Another example of a good cleaning method for some parts is the "hot tanks" of the past. They primarily used lye acid diluted in water and heated to accelerate the effect (adding heat to a chemical process increases the reaction). Lye is still available as a plumbing product to clean out badly clogged drains. However lye is very caustic and extreme caution is needed. That is why it cannot be used on aluminum, it will eat it up. But this might be another good option for your specific needs (if you only want to clean the cast iron block). I do not know what dilution ratio or other details on how to use lye for this. Hot tanks also went away due to EPA regulations.

    Actually there are a few different acids that will work to remove rust and other build up, but finding the right one for your base metals can get a little tricky. For example as mentioned the aluminum head vs the cast iron block. Too strong of a acid will ruin the relatively soft aluminum, while too weak of a acid will not remove much of the build up. For the most part in simple chemistry terms, pretty much any acid could be diluted to obtain the right level of acidity. But there are other properties of acids that come into play. This was discussed more in a related thread on how to clean an aluminum head:

    By way of comparison, I've restored some badly rusted gas tanks using either phosphoric or muriatic acids. Muriatic is very strong so it needs to be diluted more and only left in the tank for a short period. But it will remove excessive amounts rust (as well as the base metal if allowed to). For bare steel, phosphoric is great because it is less erosive and its chemical reaction with rust creates a phosphate layer that protects the newly etched metal from further rusting. Either of these could be used on a block if it is only allowed to contact the internal passages of the cooling system. But they will be more aggressive and therefore more likely to cause harm to the block or you. However if this is the better choice of agents available in your region, I can offer more information on the dilution, etc for use in fuel tanks (which might help with its use on the block).

    In your case it is the cast iron block that you are cleaning. So lye could work if you can find more information on how to best use it safely. And it may be more readily available to you locally (as well as less expensive). From what I've read oxalic acid should be another good choice for this. It is milder than lye so it can also be used on aluminum if diluted properly. In the thread I referenced earlier, I still have not had a chance to try it on the old Fiat head I have to say first hand how the aluminum head will react. But as mentioned it is used as a complete cooling system cleaner.

    Oxalic acid is available at some hardware stores as "wood bleach" (not sure about in your country). But I found that it was a very weak dilution and much more expensive if purchased that way. Instead you can buy straight oxalic acid powder online fairly reasonably priced:
    That is a US eBay listing, so you may find it different where you are. But hopefully it gives you something to reference to. And 5 pounds is more than you will need. But this works great as a general cooling system flush (entire system assembled, with engine running). So having some extra on hand can be useful in the future. And as a powder it stores well on the shelf so long as the bag is closed tightly.

    If you decide to try oxalic acid, the recommended dilution is between 4 and 8 ounces of acid per gallon of water (sorry, you will need to convert those to metric terms). For the iron block you can go more toward the stronger mixture. Use hot water and if possible distilled water (less contaminants in the water allows for more chemical reaction with the contaminants in the block). If your block is stripped bare of all bearings, expansion plugs, sensors, etc, and you plan to bore or hone the cylinders after cleaning, you could submerge the entire block in a large container full of the solution. Especially if you have rust in the crankshaft area of the block as well (for example it sat outside exposed). That would be easier, but honestly I do not know how the cylinder linings will respond...however I do not believe it will harm them. Otherwise if you only want to expose the cooling passages to the solution then you will have to plug some openings and figure the right position of the block to fill all of the cavities. Either way allow it to soak. The length of time will vary according to how much build up you have, the actual dilution you use, the temperature, etc. It may be as short as an hour or as long as 24 hours. Monitor things and if necessary refill it again with a fresh solution. The strength of the solution (amount of acid per amount of water) can also be adjusted to either speed up or slow down the process. Remember, the faster it works the more it will also eat the base metal. Overall oxalic acid is fairly safe though, compared to other acids.

    Any acid will need to be neutralized after the cleaning. First flush it thoroughly with water to remove as much of the acid mix as possible. Then some simple baking soda dissolved in water will work to neutralize the remaining acid. Similar process as with the cleaning portion. Finally flush it again with water.

    I may have a couple more references on this. If I come across any I will add them to this thread. Hopefully others will also add more to the discussion. I do not claim to be an expert, this is only what I learned when researching it for my own use. I do remember using the old cooling system flushes (oxalic acid based) from the past and they worked really well as regular maintenance. So I tend to be a little biased toward it due to some familiarity. But if you research the lye acid approach more it might be even better for your cast iron block. The old hot tanks worked with amazing results.

    Please let us know what you find.
  17. EricH

    EricH Eric Hamilton Moderator

    Durham NC, USA
    How do the various cleaning solutions affect the aux shaft bearings? If you’re just introducing stuff into the coolant system these bearings are a non-issue, but soaking the entire block is a different matter.

    Considering what a pain it is getting these bearings right, I’ve never wanted to take the chance.... I’ll spend a lot of elbow grease to avoid messing with them.
  18. Jefco

    Jefco Daily Driver

    Portland OR
    You know these are violent opposites, right?
  19. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    Ha, so true. Very poor choice of words. Bases can be as potent as acids, but they are indeed opposites. I'm not sure why lye is often referred to as a acid, but I've even see drain cleaning products state it that way. Thanks for correcting me.

    Glad you are here Jefco. Please add some info about the various agents being discussed for this application.
  20. Dr.Jeff

    Dr.Jeff True Classic

    Sin City
    I completely agree. That's why it was mentioned "If your block is stripped bare of all bearings, expansion plugs, sensors, etc, and you plan to bore or hone the cylinders after cleaning, you could submerge the entire block".

    I don't believe most of these agents at these dilutions will harm the cylinder walls, but bearings are very soft so I'm sure they will get damaged. I'd even plan on honing the cylinders at the least after a submersion.

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