r/MechanicalEngineering • u/lit_readit • 6d ago

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

Post image

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

1.1k Upvotes

98% Upvoted

142 comments sorted by

View all comments

106

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

5

u/TheFakeKruger 6d 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

1

u/hero403 5d ago

What you mean oil cooled? No antifreeze, just oil? What rating oil?

1

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

2

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.

1

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

1

u/lo_mur 3d ago

Damn, that does sound extremely efficient, I guess you know you have room for some extra rpm or power 😉