Kzang

I've been meaning to find the answer to this question ever since I've noticed on some cars water would leak or drip from the exhaust.
Someone mentioned that this is how you can tell if your cars exhaust is in good condition if you have water coming out of it.
I understand the exhaust has condensation that form, but never thoguht it would be enough to cause dripping water.
Anyone here have this with their exhaust?

Dandle

It is condensation and will normally be burnt off when the exhaust gets up to temp. If you have water dripping from it then theres enough water in the exhaust to fill the back box and its a good sign of a car that never has good runs and doesnt get up to temp very often. Not a sign of a good exhaust.

vaca

I've noticed over the years that alomost all cars drip water from the exhaust in cooler weather until they are fully warmed up. Not sure about my 530i since I'm never in a position (following my car) to notice it.

Just as an fyi, the water from the exhaust is due to the basic chemical reaction that takes place with the oxygen in the air combining with the hydocarbons (fuel)

hydocarbons plus oxygen equal water and carbon dioxide...that's perfect combustion...in reality there
s sometime a little CO (carbon monoxide), H2S (hydrogen sulfide), etc. that come out of the exhaust as well.

HC + O2 = H2O + CO2

Kzang

I was just curious since, I have never owned a car that did this.
I had a friend who bought a brand new toyota 4runner back in 1999 and when he left his car idle I noticed water dripping from the exhaust and I asked about it, thats when I was told that its a good sign when water drips from the exhaust. Since then I've noticed this from other cars while out and about and stopped at red lights.
My 535i has had some moisture just at the inside of the exhaust but never dripping water.

Dandle

It happens when the exhaust system(metal) is cold and the engine exhaust gases are hot. The moisture in the air builds up on the colder exhaust causing water to pool i.e condensation and eventually it will drip out of the back after enough water has collected in the back box. This water isnt normal water either its heavily corrosive and is what used to help rot through cheaper lower quality exhaust systems and eventually will rot through any exhaust. Any car having a decent run wont build up the water as the exhaust reaches operating temp and burns off the moisture. Where it is common is when big engine cars are used as run about vehicles and the exhaust systems dont get a chance of getting up to a good temp as the exhaust system has a large surface area and the engine is so big it runs lazy and doesnt become efficient.

sixcard

Alot of Voo-Doo floating around here!

Water is one of the products of combustion. Simple as that.

sixcard

Dandle

It is and the water vapour condenses on the colder exhaust causing water to build up and drip out of the back. If the engine is hot and the exhaust is hot then water vapour wont build up on the exhaust and you wont get dripping as it remains in the form of invisible water vapor.

DD_545i

We have a winner ! That's about as perfect a description as you can get.