Descaling of old (and porous) aluminium castings

Although this refers to the Jarama engine that I have apart on my workbench, this might be of general interest.

Looking into the water channels of my Jarama heads, it seems that there is a considerable amount of limestone in the water channels. Since the thermoconductivity of such "coating" is bad, this seriously affects heat transfer, obviously.

I am thinking about how to remove the limestone. Obviously only a chemical approach is possible. On the other hand, most aluminium alloys react with acids, like citric acid or acetic acid. Google reveals that amidosulfuric acid is supposed to be suitable for descaling of aluminium. I do not really understand why the reactivity thereof with aluminium should be less or even absent, since amidosulfuric acid is a stronger acid than e.g. citric acid, which is not recommended for aluminium coffee machine components. I rather suppose that some commercial products contain inhibitors, protecting the aluminium surface against the acid attack. I am trying to find out more details in the moment.

My main concern is that the poreous "quality" of the casting (we all know about this) may lead to leakages, because the mainly closed pores might be opened by acid action and lead to a microscopic channeling through the casting walls. Is this a silly fear?

Staatsof (through other channels) pointed my attention to CLR descaling agent. I looked up what CLR is, it contains among other components, like surfactants, two organic acids (lactic acid, gluconic acid), which have less acidity than e.g. citric acid, and by far less than amidosulforic acid. It is supposed to have contained phosphoric acid (having a higher acidicy than citric acid) in former times, but now no longer contains that. Since the acids used are of just rather moderate acidity, it presumably is less aggressive to aluminium. It probably says not to use for aluminium because there is no inhibitor for aluminium comprised.

What is your approach for internally descaling heads and/or the block? Thanks in advance for your thoughts, in particular with respect to my (perhaps silly) concerns that an acidic descaling process might turn the (poreous) casting into a sieve .....

Cheers, Bernhard

 

Many thanks for all the interesting notes and thoughts, I will have a closer look at all this in the next days.

Cheers, Bernhard

P.S.: In particular I like the proposal by BigTex, alone since it is so simple .Take my wife for a ride to the seaside (she anyway always wants to go there), drain the cooling system and fill in the sea water, ideally with a little bit of beach sand .

 

That will be interesting to hear about. In particular what kind of additives are used in the aequeous medium. I would tend to believe that they do not merely use water with a surfactant.

I recently cleaned the cases of the Weber carbs of the Espada with my christmas present, a professional ultrasonic bath, where they fit into. The grime is of quite different nature, i.e. resineous organic stuff. Some suggest that using water and dish detergent (as a surfactant) is fully sufficient. But this did not really work. After carefully raising the pH by addition of a moderate amount of sodium carbonate (for saponifying the organic grime) it worked great. "Much helps much" is dangerous and should be avoided in this case also, since aluminium is attacked in alkaline environment as well ...

So, I would guess that those guys descaling the parts from limestone by ultrasonic treatment use somthing in the solution for lowering the pH. Because ultrasonic alone, i.e. without chemical assistance, will probably not be able to (mechanically) loosen the limestone from the aluminium surface. Hopefully they do not declare their solution as a business secret and tell you what acid is used and in what concentration (and what inhibitor ,if any, see my next post).

Cheers, Bernhard

 

Yes, I noticed that too, but a statement as to that amidosulforic acid does not attack aluminium at all is for sure wrong. All acids attack aluminium to an extent depending of the acidity (wherein that of amidosulforic acid is stronger than that of e.g. citric acid, which is not recommended for coffee machines). How strong an aluminium alloy is attacked depends on the specific alloy. Some few are quite resistant again acids.

What those fellows probably do not consider is that some commercial products comprise so-called inhibitors, depending on the metal to be protected against the acid. For copper benzotriazol is well known. But I have not yet managed to find out what is used for aluminium. I will be calling a fellow in a company that makes (acidic) descaling solutions specifically for coffee machines with aluminium components and try to find out what they use as an inhibitor. If you have added a powerful inhibitor, then you can use a comparatively strong acid, like amidosulforic acid, in a relatively high concentration for resolving large amounts of limestone.

Cheers, Bernhard

 

So, I just had a phone conversation with a fellow in the research and development department of the Swiss company Durgol.

Her confirmed that Durgol Express (based on amidosulforic acid) comprises an inhibitor specific for aluminium and that, accordingly, there is effective protection against acid degradation. He specifically confirmed that there is no reasonable risk of etching microchannels by way of connecting closed bulk pores.

Aside this he emphasized that specific attention must be paid with respect to flushing after the treatment. Micropores have a high capillarity, thus a simple flush will not remove the acid from pores open to the surface. Removal will be a mainly diffusive process, i.e. take time. So between repeated flushing steps, the treated parts need to rest in the flushing water for some time.

He finally confirmed that Durgol Express is in fact (ab-) used in descaling of aluminium engines since some time and that this is without known risks due to the inhibitor and if the flushing issue is carefully considered. He recommends to dilute the solution 1:1 with water and to extend the exposition time. Finally, he emphasized that no elevated temperatures shall be applied, i.e. the treatment must be in the cold (room temperature). Thus, it should be avoided to use it, if a cooling system is operative, i.e. with the engine running.

Unfortunately he did not say what inhibitor is used .... .

Thanks to Jean-Luc Düring for spending his time with my issue.

Cheers, Bernhard

P.S.: So, I will get this stuff and fill it into the cooling jacket of the heads being placed and leveled upside down, leave it some time and flush at least three times with resting phases inbetween over night.

 

Right, just looked it up, sorry for any confusion. It was another guy doing wild (and great) things with Lamborghini engines

Cheers, Bernhard