Why the exhaust of my diesel BMW generates a wet spot on the ground?

[Saikou]

It only happens when the ambiance temperature is low (lets say under 10 degrees celsius).

It's a diesel 320d.

It doesn't throw up visible steam, it only creates that wet spot on the ground. But when I put a cardboard it doesn't get wet at all! The same occurs when I put a piece of cloth, or a mirror... they just don't get wet.

I'm kinda confused right now, bc I think it could be headgasket or EGR cooler leak to the admision... but the car doesn't burn oil and the coolant level is OK (I don't have to refill).

So what's the issue here? Car works perfectly fine, It doesn't overheat

 

[FatOrangeCat]

Most of my vehicles do the same, and I always thought it was the moisture inside of the exhaust pipes coming out.

 

[Astro14]

Hydrocarbon + Oxygen >> CO, CO2, NOx and, yep… H2O.

When the engine (petrol or diesel) is cold - the water vapor is cold, because the exhaust system is cold, and it condenses quickly - when the engine is hot, and the exhaust system is hot - the vapor stays hot. It is still there, but won’t condense on the ground or drip from the pipe.

 

[Saikou]

Hydrocarbon + Oxygen >> CO, CO2, NOx and, yep… H2O.

When the engine (petrol or diesel) is cold - the water vapor is cold, because the exhaust system is cold, and it condenses quickly - when the engine is hot, and the exhaust system is hot - the vapor stays hot. It is still there, but won’t condense on the ground or drip from the pipe.

this is why I'm concerned: the picture I attached was taken when I came home from a long trip with the engine hot, and it still created the spot on the ground.

However, when I started the car this afternoon when the sun was shining and the ambient temperature was hotter, it didn't create that wet spot...

why? Maybe bc the ground temperature has to do with the phenomena u was talking about?

 

[Astro14]

this is why I'm concerned: the picture I attached was taken when I came home from a long trip with the engine hot, and it still created the spot on the ground.

However, when I started the car this afternoon when the sun was shining and the ambient temperature was hotter, it didn't create that wet spot...

why? Maybe bc the ground temperature has to do with the phenomena u was talking about?

I would suspect so - very cold ground would cause condensation of that hot vapor in the exhaust.

I wouldn’t worry about it - there isn’t anything wrong with your car.

 

[Saikou]

I would suspect so - very cold ground would cause condensation of that hot vapor in the exhaust.

I wouldn’t worry about it - there isn’t anything wrong with your car.

it makes sense. ty