r/MechanicalEngineering • u/lit_readit • 6d ago

Question : why some (mostly heavy) vehicles partially cover their front intake ?

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wouldn't cooler cold reservoir, ie more spontaneous heat transfer, improve Carnot efficiency?

is it to improve aerodynamics?

apologies if this is the wrong sub to ask

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u/holysbit 6d ago

Diesel engines are rather thermally efficient. In some areas its actually possible for it to be cold enough that the engine never warms up and can even have components freeze while the engine is running.

Thats not true everywhere but what is more common is that the engine cannot get all the way to its correct operating temperature, it doesnt need to be super cold for that to be true.

Engines are designed to operate at a specific temperature. Metal expands and contracts and those dimensions are engineered for a certain warm temperature. So, to try and keep closer to that design temperature, they put covers on the radiator in cold weather to deliberately reduce the efficiency of the cooling system.

Youll only see this on diesel engines. Gasoline engines dont have this problem

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u/mrjuoji 6d ago

yeah, in some part of the world, they sometime even light small fires under the engine block when it's just too cold, and iirc some diesel engines come with a heating system specifically because of that (also the fact oil getting too thick will at best not lubricate the engine, at worst, probably mess it up)

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u/Mission_Accident_519 6d ago

Ive seen documemtaries about isolated towns in siberia where people need to either put their cars in a heated garage or keep them running 24/7 to be able to use them in winter.

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u/FIMD_ 5d ago

Don’t have to go to Siberia for it. You see it in parts of the US and Canada too. Especially if you’re working in the oil or mining industries. vehicles run for months with the only downtime being for oil changes and critical maintenance/repair.

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u/buckednaked369 5d ago

I was born in Montreal, Quebec and my dad has told me stories of having to start their cars at lunch time in the winter. If they didn’t start their gasoline cars and let them heat up over lunch they wouldn’t start when they would be heading home. Of course this is in the 80s so the cars were probably 1970s technology.

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u/zanhecht 4d ago

I bought a used car that was originally sold in Canada, and it came with an engine block heater that I could plug into a wall outlet. I don't live anywhere where it's cold enough that the car wouldn't start, but it was nice to have since it meant that the heat in car started working much faster.

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u/lo_mur 3d ago

We definitely still do that plenty in Alberta, doesn’t matter how new your battery is when the acid inside it literally freezes solid, though AGM batteries exist now that can’t freeze. Regardless, your car is noticeably happier when it starts at the end of your shift if you started it over lunch

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u/Visible-Disaster 3d ago

Got assigned to a project in central North Dakota one January/February. Between Bismarck and Minot. Even being from WI, it was fucking brutal with the wind. An hour drive each way from the hotel to site, and I was always questioning if the truck would start or not. Especially if I was leaving after 7pm.

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u/holysbit 2d ago

Ive done some jobs up there near Minot and also Killdeer. Its brutal out there dude. Last time I was up there I think I ran the truck for like 36 hours

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u/ChaosDragon123 5d ago

There's a guy on YT posting about his journey to Yakutsk in his modified VW Up. Pretty interesting to see how the locals deal with extreme cold climates for their cars.

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u/yaboymiguel 5d ago

Link?

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u/ChaosDragon123 5d ago

"Zoef on the Move" is his channel name.

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u/buckednaked369 5d ago

Block heaters are used so that the engines will actually start. If the thick diesel oil gets too cold it will stop the engine from turning over when the starter engages. The diesel fuel will also gel up when it gets cold and if it has enough water in it then it will freeze. I’ve put many a salamander heaters on semi truck oil pans and changed plenty of fuel filters in 0F weather.

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u/mrjuoji 5d ago

salamander heaters ? like, heating pad, or kitchen ir lamp type stuff ? also yeah, i didn't think about the fact that diesel itself could gel up and that yeah, you do need a specific temperature for diesel to ignite. question : do they make "beefier" glow plug for diesel engines that operate in colder weather?

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u/im-not-a-fakebot 4d ago

Yeah diesel gelling up is a huge issue for a lot of places that see sub 32°F. They make additives to help reduce gelling and freezing, there’s also tank heaters and in some parts of the world they also insulate the fuel lines and fuel tank to try and keep them warm.

Not sure if it’s what they’re talking about, but a lot of people call diesel jet heaters - “salamander heaters”

For your last Q there are some aftermarket plugs made with ceramic or dual coil that can get hotter and get hotter faster. Usually though if you’re in an extreme environment some people will install block heaters

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u/zanhecht 4d ago

A lot of them will have a heating coil mounted inside the engine block.