Bubbling paint on bonnet

Tony E

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Jan 14, 2005
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Looking at buying a 560SEC and bodywork is generally v good apart from a small circular area, about 2 inches across, surrounding both windscreen washer jets. Here the paintwork is bubbling slightly. I am told that it can't be rust as the bonnet is not steel (?!). In which case what is it and how do you fix it? Comments and advice much appreciated.
 

Anders

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I am almost 100 % certain that it is steel, so would suspect that it is good ol' MB tinworm...
 

jeffreyli86

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I'm with Anders. My dad used to own one of those and it rusted at the same place too... However we had ours long long ago when I was a kid... At least 10 years ago.. So if yours had just developed the rust, it must've been quite carefully looked after..
 
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Tony E

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Thanks guys

For your input. Wonder why I had two owners tell me that the SEC bonnets were "aluminium", "an alloy or something"?
Tony
 

Shude

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Wonder if there is something in the washer fluid that eats paint etc.
 

Steve_Perry

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Shude said:
Wonder if there is something in the washer fluid that eats paint etc.
Shouldn't be but if previous owners use dish washing detergent (e.g. Fairy Liquid) as a stop gap then that will really accelerate rust as it contains sodium salts.

S.
 

Brian WH

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Steve_Perry said:
Shouldn't be but if previous owners use dish washing detergent (e.g. Fairy Liquid) as a stop gap then that will really accelerate rust as it contains sodium salts.

S.

Or Antifreeze neat. :eek:
 

Satch

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Steve_Perry said:
Shouldn't be but if previous owners use dish washing detergent (e.g. Fairy Liquid) as a stop gap then that will really accelerate rust as it contains sodium salts.

S.

And, sadly, Chloride ions are really bad news for Aluminium as well. Get a salty solution trapped in a crevice
and that can be quite ugly.

Aluminium may not rust but waiting to strike some car makers is Aluminium corrosion, particularly galvanic corrosion where short cuts have been taken and Aluminium body parts are either left untreated or are not "insulated" from steel or indeed any other metal which is more "noble" that Aluminium.
 

neilrr

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Indeed, Satch.
This was the curse of the old DB series of Aston Martins with Touring's Superleggera construction - an aluminium body on a steel frame. It ended in tears. Expensive ones.
 

Satch

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Will they never learn? I understand that Ford and some other volume makers at some point took the view that since the average life of a car is 10 years or 150,000 miles they could get away with untreated aluminium alloy parts, especially in the suspension and underbody, since any significant problems were very unlikely to develop during warranty and the vehicle would be on the scrap heap (sorry, being recycled) before failure.

Aluminium corrodes very quickly (actually much more quickly than iron and steel) but the oxide that forms does not fall off like the rust on iron. A hard layer of Aluminium Oxide protects the Aluminium metal beneath.

But when salt is added to the water, Cholrine ions attack the aluminium oxide coating and expose new aluminium metal. As soon as this Aluminium metal corrodes into Aluminium Oxide, it too is stripped from the surface by the Chlorine ions. The natural protection that aluminium gets from its oxide coating is lost, so underbody parts made of untreated or unpainted alloys will often corrode quickly if exposed to road salt. Even if it is not structural, soon looks bad and they presto, spate of warranty claims from unhappy customers in those parts where road salt is used. And all that they saved was the price of a coat of paint.

Galvanic corrosion is simply unforgivable: it has been known about since the 1940's and requires nothing more than a bit of care in design and choice of materials. Of all vehicles, the Land Rover Defender and Discovery of no great age are suffering badly because for some time they had a stupid, stupid, mix of Aluminium door skins over steel frames relying on a rubber based adhesive compound to keep the two apart!




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