An off the wall question, purely out of interest:
After three years each of ownership, my two Vectra V6s had completely fur-free and uncorroded alloy engine componentry, as does my wife's ten year old 306. After barely one year however, components such as the intake manifold and cylinder head on my V70 are dulling to a white powder. Of all the cars, the V70 is the one with the best 'weather proofed' under bonnet area too, with good rubber seals along the leading edge.
Would love to know why, as I would have thought alloy components where extreme heat or loading is not a factor would have pretty well the same 'lowest cost' alloy materials, regardless of manufacturer. Thinking back in time however, Dad's 1998 S80, 1979 244, and 1972 144, all exhibited the same 'white powder' surface corrosion that my V70 does. The only exception has been Mum's (Renault 1.7 powered) 1989 440.
So, what do Volvo do, or not do with its engine alloys, please?
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Can't answer your question, but I can add a few more (mostly swedish) cars:-
1989 Saab 900 Extreme powder corrosion on intake
1991 Volvo 400 none (same as your mum's)
1992 Volvo 940 SE Turbo (B200FT) badly corroded, maybe after foolishly steam cleaned
1997 Volvo 940 Celebration (B230FK) Slight powdering
Is it a swedish metallurgy characteristic, or is it user related?
Sigma
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Correction
1989 Saab 900 Extreme powder corrosion on cam cover
Sigma
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Alloy is a very broad term, it is a mixture of metals.
Obviously that mixture could have all extremes of properties such as reacts violently on contact with water to being a liquid. The ones you mention are likely to be alloys of aluminium, all of which are obviously different alloys, with different properties/costs etc...
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The kind of corrosion you describe, where a light alloy grows patches of white dust or powder, sounds like electrochemical corrosion of different metals in accidental contact, perhaps following a leak or spillage. Maybe the Peugeot bits are less easily put in contact than the Volvo. The white powder will be aluminium oxide, which is how Al occurs in nature (bauxite).
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Dear Andrew,
Would like to know more on this if possible please. I recently viewed a used 3yr old Volvo V70 with the white powder symptoms discussed evident on the alloy parts of the engine. Is this something to cause concern? I was advised by seller powder was merely remnants of last engine wash. Powder was not evident anywhere else bar the alloy parts.
AARJAY
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I think Andrew T has got it. These types of Al alloys shouldn't really corrode much at all if in contact with water, but if they are put next to metals like iron (as in cast iron block/alloy head combination) electrolytic corrosion takes place and as Andrew says, forms bauxite (AlO2) (along with other forms of Al oxide like corundum i think).
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A possible preventative measure would be to use a laquer to keep air from cam covers etc.,to prevent oxidization.I used this method on motorbike parts in the seventies,to keep them bright after polishing.Obviously laquer needs to be suitable for the temperature involved.
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Alloy covers and engine blocks will be of an aluminium alloy. This alloy will have, my guess, in excess of 95 per cent aluminium. Alloying of aluminium involves magnesium and silicon amongst others. This makes the alloy dearer, but they are principally added to improve the manufacturing/machining and toughness characteristics of the alloy.
Alloying compromizes the inherent corrosion resistance of aluminium, but is a trade-off.
Aluminium without significant alloy content, such as ladders and heat-shields in the engine bay last very will in all sorts of conditions.
Aluminium will, in the presence of oxygen, form aluminium oxide. This forms on bare aluminium in microseconds to a thickness of a lot less than 1 micron and then stops growing. The reason it stops is because al-oxide is impervious to most oxygen and most chemicals.
If you compromize the Al2O3 by using some 'engine washes' (they can be caustic) it may not reform correctly and be open to continued attack. This is evident as the white deposit that you see on the alloy.
The white deposit is not deterimental to the function or the longevity of the component in the engine bay in the same way that rust on iron is.
It's an aesthetic thing
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