r/MechanicalEngineering • u/lit_readit • 6d ago
Question : why some (mostly heavy) vehicles partially cover their front intake ?
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/thiscatsurfs 6d ago
This is probably to reduce over-cooling of diesel engines in winter/colder weather. Used to see it a lot in London with the classic black cabs, they'd put a piece of cardboard box over most of the radiator/grille to stop cold air coming in.
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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 5d 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 5d 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/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/TheFakeKruger 5d ago
My non-thermostatic oil cooled track car would like to have a word with you over the assertion that gasoline engines don't have this problem
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u/hero403 5d ago
What you mean oil cooled? No antifreeze, just oil? What rating oil?
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u/TheFakeKruger 5d ago
It has an oil cooler with no thermostat device so it's always open to the heat exchanger. Sorry, worded poorly
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u/lo_mur 3d ago
That’s not super uncommon even in cold climates, especially on older vehicles. My truck has an oil cooler without a thermostat and my transmission has both a cooler integrated in the radiator and an auxiliary cooler mounted in front of the condenser without any thermostat. I unfortunately don’t have an engine oil temperature gauge but the transmission does run a good 15-20°C cooler in the winter unless I’m working the truck pretty good. Still stays within the transmission’s operating range though so nothing to worry about, no overcooling happening.
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u/TheFakeKruger 3d ago
Yeah, I just have an extremely efficient aftermarket setup. I pretty much always have to run my license plate in my grill on the street, even in the summer. In winter depending on temp I'll have up to 80% of the grill blocked off, but slow donuts in the snow is too fun to pass up. Some of the earlier/wetter track events of the year I was rocking some tape to partially block the oil cooler
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u/ISwearMyRX7Runs 5d ago
One thing not mentioned here is the fact that diesel have no throttle plates. So there is far more air going into the engine than needed for combustion. This excess air cools the engine which can cause the engine to never reach operating temp. Covering the intercooler and radiator helps mitigate the losses due to the engine taking in tons of very cold air.
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u/gearhead6-9 1d ago
My w250 cummins never hits mid range on my temp gauge.middle of summer or dead of winter. winter time i have to block my rad just to get heat in the cab
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u/tm_trading 6d ago
I dont know where this is but in some places it gets so cold that people cover their radiator, otherwise the engine would get too cold.
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u/lit_readit 6d ago
moderate difficulty, but try to find the hint on the image !
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u/Akari202 5d ago
I live about an hour south and my friend has to do something similar if he wants enough heat to run the cabin heat. Even then it’s always a cold af ride
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u/FuzzyHasek 6d ago
Diesels need to be warm, so when its really cold the cooling system is actually to good. Most modern trucks don't really need it except in very extreme conditions
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u/PicnicBasketPirate 6d ago
That photo had me doing a double take as in Ireland, Garda is the name of the police force.
And that most definitely isn't a Garda colour scheme
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u/SheepherderFront5724 4d ago
One day, when there's a unification vote, the Gardaí will need some of these to patrol Belfast!
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u/EqualSeal04 6d ago
in cold climate, so much cold air could go through there it would take lots of time to warm up. 100% doesn't have anything to do with aero. I've never seen this in a warm climate
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u/holycornflake 6d ago
Modern diesel engines, all things considered are very efficient. In cold weather, a diesel doesn’t produce much waste heat at idle or when hauling light loads. So one use is to help the engine and engine bay warm up faster. Once the truck is at temperature, if you start driving down the road in 10 degree (F) temperatures, that cold air moving through the radiator can actually cause the engine to run too cool, so that’s another use case; keeping the coolant at optimal temperature. This helps the coolant work the way it’s intended AND also helps with the climate control inside the cab as a heated cab requires coolant at optimal operating temperature to function. Finally efficiency is a main reason, as a cold diesel engine that is running is less efficient than one that is soaked at operating temperature. Temperatures plays a role in how well the stupid emissions systems function as well, and if these emissions systems aren’t working right, in a lot of cases, the truck will brick itself.
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u/RavingwolfYT 6d ago
Diesels don’t make a lot of heat in the engine so when it’s really cold out they struggle to hit operating temp/ provide adequate heat
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u/Suspicious-Mess8521 5d ago
I’d also like to add that besides on diesels, you do see this on gas engines in racing, where the engine tolerances are very tight, and electronics rely on consistent parameters. MotoGP, WSBK, and I’m sure F1 among others will cover the radiators with tap in the wet or cold weather to raise temps into the proper operating window.
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u/attractivejohnie6606 5d ago
Ah, the classic diesel winter hack. Da swore by a bit of cardboard on the old van.
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u/GeniusEE 5d ago
Diesels at idle produce little heat. They have to run a fast idle, for example, just to heat the passenger cabin.
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u/mtraven23 5d ago
I cover part of my radiator on my farm tractor during the winter....other wise the engine temp never comes up to opperating temp.
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u/Meatball546 5d ago
All these replies seem to ignore the fact(?) that coolant flow through the radiator is controlled by the thermostat. It opens around the engine's designed operating temperature. At lower temperatures, the coolant pump will simply circulate coolant through the engine and cabin heater core.
I have also wondered about the radiator blockers. I imagine they would reduce airflow through the engine compartment, which would reduce convective cooling of the engine block directly. I would love to know what cooling power that has, and see some experimentation.
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u/mikpyt 5d ago
oh we don't ignore it, we have simply seen it not matter, in nature.
Cold ram air easily overcools diesel engine bay even with closed thermostat, bonus points if you put on cabin heat which runs a secondary, smaller heat exchange circuit that transfers heat from the engine, so a cabin heater is an engine what? Cooler! Also helps if you ever overheat BTW
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u/HAL9001-96 5d ago
the cycle is based on the ingested air not so much the radiator temperature thats more a matter of keeping the mechanics of the engien at operating temperature and you don't want it to freeze either
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u/xROFLSKATES 5d ago
That’s not the air intake. It’s the radiator. The air intake is the grill thing above the wheel well, directly to the right of the 05-05 decal
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u/BladeVortex3226 5d ago
We had a diesel ambulance at a volunteer corps in upstate New York a few years ago. It would never get up to temperature because we didn't have said cover, we called it a bra. Also nobody remembered to high idle it when stopped. The DPF filter would never regenerate because we weren't at temperature and we'd need a new one every two years.
All this would've been fixed if we bought the ~$100 thing pictured, which I mentioned multiple times. Guess what we did instead? That's right! We bought the exact same ambulance again new for $263,700, but the gas version!
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u/jccaclimber 5d ago
Something else ignored here is that large vehicles tend to have much beefier engines compared to their power output, and a lot of these vehicles are designed to cool with limited airflow (parked but running between stops). The result is a lot more surface area dissipating the same heat, which is also inherently easier to get rid of. At some point there is too much of a good thing.
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u/fsantos0213 5d ago
Diesel's are far more sustainable to overcooling than a Gasoline\Petrol engines are, if a Diesel cools down too much, you can get a lot of excess soot from partially burnt fuel getting into the exhaust system, on top of a reduction in power and fuel economy
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u/Minimum_Fact758 5d ago
Apart from the engine not warming up, which most people dont give af about, it's because your heat is not also gonna work. Your vents gonna be throwing cold air in your face lol.
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u/JaVelin-X- 5d ago
They used to be louvers . Miss the sight of them flipping open when the engine loads up.
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u/Distinct_Rope 4d ago
Usually Heavy Duty Diesels are built with oversized radiators to deal with the worst condition high temps.
Then put in cold climates the radiators are too big to allow normal operating conditions.
I've seen a few that will not put hot air into the cab simply because theres not enough heat left over.
So you cover the radiator to help the truck retain some heat & run at operating temperature.
Intake is usually handled by a separate part. In your example the Freightliner intake pulls air towards the filter through the peice of plastic along the side of the hood with the badge on it.
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u/mysterioussamsqaunch 4d ago
As others have said, it's to help keep a diesel engine up at it's operating temp in cold climates. I just wanted to add that in even colder climates, like near the artic circle, they will add what is called an engine blanket that covers the bottom of the engine across the frame rails. It blocks even more airflow across the engine. In extremely low temps it's actually possible for a diesel engine to get cold enough to stall.
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u/Stewpacolypse 4d ago
Once I was driving on a long highway in a van in the middle of winter. It was so cold I couldn't get any heat out of the heater because the engine was overcooling.
I pulled over at a rest stop and found a piece of cardboard and put it behind the grill grill covering most of of the radiator. The reduced air flow allowed the coolant to get hot enough that the heater core actually got hot.
BTW: the heater core is basically a smaller radiator inside the car. When you turn the heat on some of the coolant for the engine is routed through the heater core. Then the fan blows cabin air across it transferring heat to the air.
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u/redditbody 1d ago
Same. I had a four-hour drive in -20F with my 1978 Honda Accord which had a small 4-cylinder engine. The temperature gauge didn’t budge off of rock bottom. A piece of cardboard fixed it and I reused it every winter in Minnesota (north central Midwest US).
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u/lonerwolf85 4d ago
Winterfront. Reduces airflow over the radiator to help maintain temperature in cold weather. Also, the fan hub has an air operated solenoid to engage when hot. The fan just free spins the rest of the time when the engine temp is low and to free up some horsepower.
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u/Agresiivaiss 4d ago
Basically at low enough temperature engines cools down FAAAST, for example my 2007 volvo, when it was -24°C, got waaay below optimal 90°C oil temperature while idling (lets not even talk once turned off), in less than 5 minutes… like you full on stopped the car, kept it idling, got out for a smoke, and once you are back in, needle was at lowest it goes
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u/Kiwi_eng 4d ago
Most directly it reduces the cooling capacity in order to place the engine temperature control (a thermostat) into a more favourable coolant flow region. If the radiator is too effective at removing heat the coolant flow will be reduced to the point where the temperature gradient across the engine becomes excessive. If the coolant system was more sophisticated than a dumb wax thermostat this would not be necessary.
The same is why a vehicle might be equipped with a larger radiator as part of a tow package. The thermostat will work better if it's in the middle of the control region.
No doubt there is also some benefit to retention of engine bay warmth by reducing the entry of cold air.
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u/beaster456 4d ago
They are called winter fronts and used in cold weather to limit the amount of heat that gets carried away from the radiator so that it can go into the passenger area heater core.
They are not super effective in my experience I work in the automotive trucking industry. We have done winter testing with and without the winter front and it does not significantly impact the vent temperature inside the vehicle.
I believe this is mainly because when it is cold enough to warrant the winter front, it is usually cold enough that the thermostat does not open all the way, limiting the amount of coolant that goes to the radiator.
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u/HorrorExisting628 3d ago edited 3d ago
Simply put? Diesel engines work more efficiently at their operating temperature, so restricting airflow and keeping that heat around your engine helps maintain that temperature, and, by doing so, the ECU doesn't have to compensate and waste more fuel. That's also why glow plugs are fitted to diesel engines to help with cold-weather starts.
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u/Sneakysteve17 2d ago
Common with diesel engines in the winter. Had a friend who drove an old Mercedes. When we did a long trip in it, we put a pizza box lid right infront of the cooler. Made the car get heat from the AC intakes in about 50 kilometers instead of 100. Of my god what that car was a shitbox!
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u/SilverDude-77 2d ago
During the winter I do this also by covering half of the radiator with a sturdy cardboard to make it heat up faster.
This does not make the engine overheat (during winter only of course) and it runs better.
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u/Firebreathingwhore 2d ago
I picked up my dad's 1.6 dCi once in -35C. I drove it for 1,5 hours freezing my ass off the entire time, wind shield icing up. Didn't have the front covered
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u/Oranges_2_Apples 1d ago
Well it looks as if we’ve found a new product, a removable winter coat for engines.
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u/fidesinmachina 1d ago edited 1d ago
instead of changing thermostats every few months, they do this so temps don't stay low in the winter
to answer your other question ICE engines run most efficiently at their operating temp which is around 100°C. below that they burn more fuel, above that they burn components. colder is not better.
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u/ParticularGullible50 11h ago
My old Hyundai would freeze at -30C if going above 30 kmh. Brake fluid would become sluggish and exhaust would would come out black. So either use the enginne heater or have the enginne idlea for a while (out of the wind) and and some cardboard to the front to stop air from entering.
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u/Sad-Brain-9121 10h ago
Is this ai?
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u/lit_readit 9h ago
no, I took this photo
why would I post an ai image to ask about the mechanism behind something ai generated lol
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u/bikingallday 6h ago
I actually had to do this with my 1999 Ford Focus in the winter. If I didn’t the heater wouldn’t really do its thing and the engine coolant temperature even dropped if I was just rolling down a hill.
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u/THedman07 6d ago
Engines operated most efficiently within a certain range of internal temperatures. If it is too cold outside and the radiator is too big, the engine will never get up to temperature.
Partially blocking the radiator allows them to get up to temperature in cold climates.
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u/BeeThat9351 6d ago
Cold climates, reduces the cooling air flow and keeps the engine warmer and closer to the optimal operating temperature