car exhaust??

[dannyr]

well off topic but I think many here will have answer to my idle curiosity -----

I've seen car exhaust tailpipes dripping before, but today was following a fairly recent Merc diesel saloon round our ringroad and liquid was pouring from one tailpipe every time he accelerated even slightly --- what's this?? No 'smoke' and car seemed to function OK.

A cold dry sunny day here with no serious puddles, and his car wasn't shiny so hadn't just been to car wash

 

[Richard_C]

Water vapour is a product of combustion in the engine. Fuels are mostly carbon and hydrogen based molecules, add oxygen from the air and what emerges is carbon dioxide (+ some monoxide) and good old H2O as vapour.

It condenses in the exhaust system until that system is hot, then it evaporates and comes out invisibly. What you have seen is a car that is still pretty cold after start up with condensate dribbling out. Maybe its only been used for short trips in the last few days so there is more than one startups-worth of nasty acidic stuff slopping about in the tubes.

If you mostly do long trips or lots of engine-hot short ones like a delivery van your exhaust bits last a lot longer than if you just a few short trips each week and never get it all properly hot.

 

[dannyr]

Thanks - I know my chemistry, just never seen it pour out like an open tap, but I'm sure you're right, just combustion product.

 

[OldWood]

Is it also possible that this is a modern deisel Merc which adds urea to the exhaust to reduce nitrates (?) and maybe when cold that produces more 'water'. They won't go anywhere unless the urea container has fluid in it.

 

[Lons]

Is it also possible that this is a modern deisel Merc which adds urea to the exhaust to reduce nitrates (?) and maybe when cold that produces more 'water'. They won't go anywhere unless the urea container has fluid in it.

As above
My Merc uses AdBlue which is deionised water and urea, the car won't run without it and it's injected into the exhaust gases to reduce emissions specifically NOx which it converts to water and nitrogen, as said when the engines are cold the water runs out of the exhaust rather than evaporates. There's a noticeable difference in my car in different temperature conditions.

Petrol cars push water out of the exhausts as well but it's less obvious.

 

[minilathe22]

As a small child I once got a watering can and poured water into the tailpipe of my parents ford fiesta, "just to see what would happen". I had put enough in that it refused to turn over... I see many modern cars with a tailpipe that curves sharply downwards, I wonder if its to avoid that kind of thing! I forget what the solution was now, I think they rocked it back and forwards until some of the water came out...

 

[clogs]

just what ya need to rot exhausts....hahaha....

 

[dannyr]

Thanks for the replies - learnt something today.

Yes, combustion products, but as it was a recent Merc, I think the NOx reducing urea might be what made it different.

(My old Skoda might sometimes smell of pee because I'm carrying compost to the allotment etc - but don't stand behind a modern diesel Merc if you want to avoid a similar whiff??)