Tuesday, January 24All That Matters

Went to the store during a snowstorm, came back to these weird patterns on the hood of my car

Went to the store during a snowstorm, came back to these weird patterns on the hood of my car

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  • JPF04STi

    It’s usually where all the bracing and structure of the underside of the hood is. All those spots likely correspond to where the skin of the hood meets the lower structure of the hood. The multiple layers of metal will hold heat longer, so if the car is warm, the snow will melt faster in the slightly warmer areas.

  • Zytheran

    Ex automotive engineer here. (Specifically a guy who spend many years working on a manufacturing process to make engine hoods.)

    Some background: The hood of a vehicle is typically comprised of 2 thin metal layers. There is the inner and the skin. Together they are meant to form a stiff unit that will crumple in a controlled manner during a collision. When you join two pieces of thin steel together where it touches will be less stiff than if you separate it. Basically it will fold in the areas of lesser stiffness, which is what you want. During a crash each time it folds along one of these deliberate weaknesses it absorbs energy from the collision. The overall aim in a collision is to fold up steel and anything else, absorbing energy as you go so there is no energy left to crush the passenger compartment with the fragile / weak humans. Now a problem with thin metal is that it reverberates and drums, causing annoying sounds. So the fix to that is to put a heat cured expanding polyurethane, a sound deadening material, between the panels when you make it. When it goes through the paint oven it expands and goes hardish, not brittle, not soft but firm. IT seperates the panels preventing rattles and reducing drumming sounds.

    Side issue: Around the edge you’ll either spot weld after running through a hemming press (old school and crap because it needs finishing after, US) or use a 2-part epoxy with small beads of glass in it (Oz/Holden FTW) because that removes the need for finishing the spot weld burns because the adhesive glues the panels together with the aid of the glass beads that embed themselves in the steel during the press operation. There are weaknesses along the edge to encourage folding in the correct area to get transverse folds.

    What’s happening here: These sound deadening areas between the two panels are put down by robot (usually, in decent car plants at least) and are in the shapes of the crescents in the photo. The reason you get less snow there is that those areas are still warmer because the sound deadener holds heat and transfers relatively more heat (it’s a solid) from the still warmer engine compartment to the outer skin. The areas not connected end up with an insulating air gap (gas) allowing the skin to cool more through radiating heat away, retaining the snow on top.

    Edit: Just to be clear about the aliens many are commenting on, different species like having sex on engine hoods of different brands, don’t ask me, I’m not a xenobiologist, it’s just their thing. Multi-tentacled species seem to like Mercedes, again no idea why, I would have thought they prefer Japanese cars but there you go. That’s why they’re alien.

  • GrubEatingBird

    I noted this pattern on roofs in the area. Snow sticking in line with the rafters. Insulation between them kept those areas warmer so the snow melted there

  • thewesman11

    Sometimes hoods are reinforced underneath in weird grid like patterns. I bet if you opened the hood the internal pattern would match the melted snow pattern. I imagine the reinforcement acts as a bit of insulation.

  • Rygel17

    Its the welds under your hood holding on the insulation and attachment points. Your hood isn’t just a peice of sheet metal covering your engine, there is a structural support holding its shape and damping engine sound and heat.

  • legionzero_net

    Those are the places where heat retaining structures are under your hood. They take longer to cool and melt the snow as it hits the hood.

  • gardenina

    The AI in your car’s computer has gained sentience and is attempting to make first contact with you. It’s the Singularity!

  • spacedirt

    Open your hood and look at the underside, you’ll notice the patterns in the snow-covered top mimic exactly the pattern of the insulation installed on the bottom side of the hood. This happened because you hood gets warmed by the engine (due to recent driving) more in the places with less insulation, this causing the snow to melt in those specific areas first.

  • george1044

    Hello former automotive engineer here. You see the engine hood is actually made up of various types of metal to make it cheaper. The alloy thus has various temperature constants depending on the density of every metal. Additionally, they tend to coalesce around specific areas due to their hydrophobia. This entire practice was invented back in 1998, but don’t let that distract you from the fact that in that same year, in 1998, The Undertaker threw Mankind off Hell in a Cell, and plummeted 16ft through an announcer’s table.


    Lol those are hood framing, it’s for support so hood don’t twist lol it’s under that black carpet stuff for sound dampening. This shits could been known but common sense is gone if you never open a hood

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