SUV John

Checking out how my hood opens following another topic on the extended opening position available, I came across an unexpected observation.

I recently had picked up a rather handy (and bright) magnetic LED light from a local Menards and keep it in the vehicle to use as needed under the hood or wherever, but found the hood to be non-magnetic. The fenders are steel and therefore magnetic, but I found it interesting that the hood is not.

I now wonder what other interesting things there are to be discovered on my first Mercedes-Benz SUV.

chassis

The fuel filler door/flap is plastic.

Notice how much plastic is used under the hood, meaning brackets, attachments and mounting hardware.

Notice how light the factory floor mats are.

These points are not criticisms of M-B, the increased use of plastic and lightweighting is happening with all carmakers. What is noteworthy to me is the increase in the use of plastic and overall lower weight of components, compared with vehicles made 5, 10 and 15 years ago. Reducing vehicle weight is one tool carmakers use to achieve fuel economy and emissions regulations, at the same time offsetting weight increases from content additions such as nav systems, power liftgate actuators, sophisticated LED headlamps, and others.

E55 KEV

I believe the hood is Aluminum, which a magnet will not adhere to, including the tail gate.

chassis

Yes, and I believe the door skins and quarter panel outer panels are aluminum.

GLE43_Sube

Are you saying the tail gate is aluminum too? Mine is steel.

GLE43_Sube

Just checked the whole vehicle with a magnet. The only thing I found that was not steel was the hood (aluminum), the fuel filler door and both bumpers (plastic).

E55 KEV

My bad. I was thinking of my W212 E63s which has an Aluminum trunk and front fenders.

SUV John

Given the aluminum hood, I would have thought an aluminum tail gate would have made sense too. Otherwise, I wonder what the point of just making the hood aluminum is.

The doors are more likely to rust than the hood, so as far as resistance to deteriorating goes I would have thought for Mercedes to make the hood steel and the doors aluminum--- or ALL doors aluminum. With the right grade, all aluminum would have made for one durable vehicle.

GLE43_Sube

The aluminum hood was obviously for weight reduction, and maybe cost too. For reasons of safety, I don't know if I'd want aluminum doors or an aluminum tail gate. Aluminum is a very soft metal. Anyone old enough to remember steel soda cans compared to today's aluminum ones can attest to that. In the front, you still have the engine, steel fenders and the frame for added protection. In the rear, all you have is a Styrofoam filled bumper. There's not much to the doors either.

chassis

Vehicle side intrusion is a deeply engineered topic. Side intrusion beams using high strength steel are in the doors. Energy absorbing polyurethane is nothing like styrofoam. A 100% aluminum body is possible, as is a 100% composite/carbon fiber body. M-B and other carmakers use the combination of materials to meet the many requirements of a vehicle (front, side and rear impact, fuel economy, emissions and others, not the least of which is cost).

johbe646

@GLE John Living where they put salt and sand/gravel on the roads 5-6 months of every year makes me wonder why you think aluminum in the doors is more important than the hood/front, from a rust point of view. Not interpreting your post as negative or ironic, just curious.

But, on topic, imo aluminum body parts is a selling argument these days, at least east of the pond. Has been for years.

/J

skw

Jaguar, Land Rover, and Audi all use aluminum bodies on some of their models.

SUV John

The answer is simple, aluminum does not rust, steel does. Ford and other makers as well have used aluminum for years. The grade of aluminum is what is relevant and as technology develops I wouldn't be surprised that aluminum and other metals are used. There are even some cars, Corvette for one, that use some plastics on suspension parts while most people associate plastic being soft and weak. There's always more to something than what's on the surface.

SUV John

Aluminum is only as soft as the grade and thickness is, which is why all aluminum airplanes, like the ones I worked on stay together and fly at the altitude and speeds they do. There are cars using plastic suspension parts that are evidently durable enough so the specific material grade and other factors have to be taken into account when determining strength and durability.
It's all good, we're surrounded by a lot of airbags

chassis

Another data point - the Corvette Z06 offered the first iteration of an aluminum space frame in 2005. Heat treatment and alloying metals deliver strength, hardness and other properties. There are no carmakers using pure (elemental) aluminum.

johbe646

Yes. Of course. My question was not if aluminum rusts, it was about why you pointed out that doors will rust before the hood.

Maybe they do, but hoods and noses are plastic and aluminum these days too, with extra think coating, or at least I think so.

Am I contradicting myself now? And does anyone want argue about aluminum vs aluminium for a while?

/J

SUV John

Sorry, I thought it was more obvious than that and probably shouldn't believe that everyone knows about cars rusting or lives in an areas where road deicing chemicals are applied.

Since you asked, the doors splash up road salt and other winter deicers used locally and that then stays there for a period of time. Road debris compounds the problem causing the lower areas of the door to rust out before the hood, being higher off the ground, stays protected and remains cleaner as well.

The hood and bumper don't need the corrosion resistance of the materials they are made from, the benefit it weight savings.

No need for anyone to overthink materials versus corrosion resistance, all that's being discussed is the observation of what Mercedes used.

Thanks for your input and enjoy your Mercedes!

GLE43_Sube

This is certainly true. Along those same lines, after a washing or driving in the rain, I dry the door wells and leave all of the doors open overnight. Your doors have drainage holes at the bottom. This lets the water properly drain, instead of accumulating in the door wells. I once had a car develop rust in a door well.