Mercedes - Galvanic corrosion? - John F

Unlike their lighter long-lasting all-aluminium competitors, I see Mercedes have attempted to catch up with bodies which are now a mixture of steel and aluminium. Does anyone know how they are able to prevent galvanic corrosion at the joins? Is there not a risk of hidden structural weakness beyond, say, ten years old?

Mercedes - Galvanic corrosion? - focussed

The only way to prevent galvanic corrosion would be to completely isolate the steel from the aluminium.

Joining together different metals or alloys may result in rapid galvanic corrosion on the less noble alloy, the aluminium, which will act as a sacrificial anode relative to the nobler, cathodic alloy, the steel.

Necessary conditions for such corrosion are that the two alloys stay in electrical contact and that an electrolyte such as salt water or a film of moisture is present. Insulating flanges and bolts, coating, or dry conditions, will prevent galvanic corrosion from occurring.

Not impossible to achieve but makes manufacture and assembly more difficult.

Mercedes - Galvanic corrosion? - RT

The "all-aluminium" cars have plenty of steel components bolted to them.

Mercedes - Galvanic corrosion? - gordonbennet

We looked (not for long) at Merc's W215 CL500 a few years ago to replace the now 20 year old W124 coupe we still have.

Didn't look for long, found a 3 year old CL500 we liked the look of, aluminium panels over a steel frame, rear wheelarch a chunk roughly 6" long had corroded completely away and i mean vanished and continuing to crumble away, and on both rear quarter panels presumably where the steel frame inside touches there was signficant bubbling of the paint from deep inside...sales bod seemed amazed that i'd spotted that in 30 seconds and we were walking away some 30 seconds later, never bothered to lift the bonnet or boot though maybe that might have been worth it just to poke fun at this piece of quality German engineering when i found more disasters in their infancy.

Our lorry tanker trailers are aluminium ladder chassis, what they gain in weight saving i'm not at all sure is cost effective, they suffer with terrible salt corrosion and gain expensive cracks in quite short order.

The pressure tanks themselves are aluminium but very well painted and being high up don't suffer with salt ingress anywhere near.

I'll stick with properly painted all steel cars thanks all the same, hopefully with some decent wax injection by the maker when new.

Mercedes - Galvanic corrosion? - RobJP

I fail to understand why any manufacturer would design and build a mixed-metal car like that. The issues are well-known, and have been understood from a chemistry point of view for 200+ years, and observed back as far as Samuel Pepys's day !

With the market for carbon fibre growing at an extraordinary rate (and thus costs dropping at a similar rate), it really makes no sense to me to make some car parts from different metals.

A work colleague of mine had a 2001 Laguna, which I seem to recall had a plastic bonnet to save on weight. Seems more logical than chancing a car disintegrating before your eyes.

Mercedes - Galvanic corrosion? - Ethan Edwards

Yes the Aluminium dissolves away. It's a sacrificial anode. I've often thought that a mixed metal vehicle would be a disaster long term.

Mercedes - Galvanic corrosion? - corax
A work colleague of mine had a 2001 Laguna, which I seem to recall had a plastic bonnet to save on weight. Seems more logical than chancing a car disintegrating before your eyes.

Mercedes could learn from the French car makers on how to design corrosion resistant bodies. Say what you like about their electrics, but it's very rare to see a rusty Renault, Peugeot or Citroen.

Mercedes - Galvanic corrosion? - gordonbennet

Very true Corax, still lots of 405's running round with starship miles and rust free.

I think many makers go through these patches of up to a decade or more when for one reason or another they lose the plot and make sub standard cars whilst trading on their previous good names.

Merc's years of woe what 96 to 2006?

BMW's engine problems in the noughties.

VW's problems more recent but seeing as they have so many models its seems never ending.

Mazda and Toyota Diesels some of which should be avoided, PSA's 1.6 Diesel of doom no matter which make its fitted to unless serviced half the recommended intervals....many modern Diesels suffering compression blow by, i always thought it stupid to put injectors inside the engine, when fitted outside like a spark plug its immediately obvious if a seal leaks.

Renault and PSA electrics in the noughties.

All makes electric parking brakes, automated manual boxes etc etc.

What i can't fathom is when a company finds the winning formula, eg Pug's 405, VW's 1.9 PDi, why not basically stick to and build on that formula and only replace it when the new model/engine is proved beyond all doubt to be better in every way and most importantly lasts, if it aint broke don't fix it.

Mercedes - Galvanic corrosion? - John F

Very true Corax, still lots of 405's running round with starship miles and rust free.

We had a brace of 309's for my two sons - both were well into their teens when sold, (cars, not sons) and still no rust at all! How did they do it?

Perhaps HJ might ask for an authoritative reply from Mercedes as to whether this is actually a clever bit of planned obsolescence?

Mercedes - Galvanic corrosion? - slkfanboy

Very true Corax, still lots of 405's running round with starship miles and rust free.

We had a brace of 309's for my two sons - both were well into their teens when sold, (cars, not sons) and still no rust at all! How did they do it?

Perhaps HJ might ask for an authoritative reply from Mercedes as to whether this is actually a clever bit of planned obsolescence?

I can say the the 405 that I had from new was truely bad. The non stick paint used needed a respray after only 3 years. The rubber band used for a clutch cable defied smooth gear changes. The constant elec. issues and the list goes on.

Mixed metal car have been around for a while and I've had a few with no issues. Can't say the A2/Jag was any worse or better or worse than any steel merc.

Mercedes - Galvanic corrosion? - corax
What i can't fathom is when a company finds the winning formula, eg Pug's 405, VW's 1.9 PDi, why not basically stick to and build on that formula and only replace it when the new model/engine is proved beyond all doubt to be better in every way and most importantly lasts, if it aint broke don't fix it.

Emissions regulations saw to the PD engine, and indirect injection engines. The cam operated injectors on the 1.9PD couldn't be controlled by the ECU to fire multiple times like a common rail system to promote an ever more efficient burn. It's the same with many successful reliable engines, in the end the regulations kill them off.

The manufacturers want you to buy a new car and aren't interested in making a car that lasts, although in the past I think there must have been a certain pride among good engineers and management to make a car that lasted, i.e Mercedes

As you've highlighted above, there are times when things go wrong. You'd love to be a fly on the wall to hear the conversations between the key people responsible for those problems at the time.

Changes of management, how much influence the engineers have, how good those engineers are, overly severe cost cutting measures, it's understandable how manufacturers can sometimes go through a bad patch.

Edited by corax on 07/07/2016 at 19:35

Mercedes - Galvanic corrosion? - Wackyracer
The manufacturers want you to buy a new car and aren't interested in making a car that lasts, although in the past I think there must have been a certain pride among good engineers and management to make a car that lasted, i.e Mercedes

I was having this conversation this morning, what a manufacturer deems to be the lifetime of a car.

I would guess they factor in that by the time the corrosion becomes a problem the car is (in their opinion) at the end of it's life.

I'd like to know what Mercedes say is the life of one of their cars.

Mercedes - Galvanic corrosion? - RT

I was having this conversation this morning, what a manufacturer deems to be the lifetime of a car.

I would guess they factor in that by the time the corrosion becomes a problem the car is (in their opinion) at the end of it's life.

I'd like to know what Mercedes say is the life of one of their cars.

"Lifetime" is however long, or short, it lasts - it's a marketing BS term, not an engineering one.

Mercedes - Galvanic corrosion? - RobJP

I always view 'lifetime' or 'filled for life' (think BMW's gearboxes from a few years back) as 'designed to fail when we can't be held legally responsible'

Mercedes - Galvanic corrosion? - focussed

The "all-aluminium" cars have plenty of steel components bolted to them.

Yes they do and one example I can think of because I recently researched it is the serious corrosion caused by steel front lower wishbone mount shims(steel) to the chassis (aluminium) on a lotus elise/

Mercedes - Galvanic corrosion? - sandy56

I believe the later jag XJ sufferes this problem, as described by HJ.

Mercedes - Galvanic corrosion? - barney100
How many old Mercs compared to old French cars do you see?
Mercedes - Galvanic corrosion? - madf
How many old Mercs compared to old French cars do you see?

My next door neighbour has an immaculate (yes really ) expensivley restored Mercedes 300E c 1988.

No-one in their right minds restores an old Renault.

Mercedes - Galvanic corrosion? - focussed

Out in the countryside in north-west France where I am it is quite common to see a lot of old French cars and vans still going as daily drives , not just as classics, Renault 4's and the odd early Renault 3-early Mk1 Renault 5's mostly because there is no annual road tax in france, but there is a registration tax on change of ownership so the older locals avoid changing their cars.

The rural French don't do "keeping up with the Joneses" with their cars, so if it keeps going they keep it - the annual expense is just fuel, maintenance and minimum legal insurance with the mot every two years, so it's cheap motoring.

Mercedes - Galvanic corrosion? - Wackyracer

The rural French don't do "keeping up with the Joneses" with their cars, so if it keeps going they keep it - the annual expense is just fuel, maintenance and minimum legal insurance with the mot every two years, so it's cheap motoring.

That sounds almost like me, same Citroen for the last 15year and 4 months. Almost looks as good as the day I bought it, runs like a swiss clock. Why on earth would I want to spend loads of money changing it for something new? I'm sure my neighbours think I'm mad as they change their cars regularly but, I spend half of what their monthly payment is on my yearly servicing.

Mercedes - Galvanic corrosion? - barney100
So Merc 28 years young. Compare keeping that to changing every 2 years!