Black watery exhaust emissions

[Owlsman]

After trying the full range of garage floor paints, all of which proved to be only marginally better than useless, I am just about to lay a new garage floor using those hard rubber tiles that all fit together like a giant jigsaw puzzle. I'm hoping this will be a 'once and for all' solution.

Naturally, I will want to keep my shiny new floor looking good for as long as possible but this is going to be tricky because immediately on start up, sooty black water comes out of the exhaust and it leaves a spluttered black trail all along the garage floor. I rarely need the choke to start and usually drive straight out of the garage when the engine has fired. Anything at the back of the garage, within 3 or 4 feet of the car, soon get splattered in a black sooty deposit.

Am I correct in thinking that this is a sign of the mixture being too rich? Or is it a natural consequence of cold steel (exhaust) meeting hot burnt fuel gases....and if so, why does this not happen on my 'modern'? When returning the car into the garage (after a run and when everything has warmed up) there is no sign of any deposits.

As ever, any thoughts welcome please.

Thanks,
Alan

[kennatt]

modern has cat absorbs the carbon,normal in non cats on cold start up

[ampwhu]

put the car in the other way so the exhaust is facing outwards.

[philthehill]

It has to be remembered that for every gallon of petrol you put in the tank a gallon of water comes out of the exhaust.

When the engine/exhaust is hot you will not see the water but it is still coming out of the exhaust as clear steam/vapour.

The water will drag any black contaminates out of the exhaust and that is why you have black water coming out of the exhaust when the engine is cold.

[kevin s]

Even a modern car will do it, especially if it's only been used for short journeys, I once took my wifes mazda on a run after she had been using it for short journeys, when I hit the motorway I thought I had blown it up, vast clouds of white steam coming out of the exhaust, after a couple of miles it all cleared and all was fine.

If you want to avoid staining the floor you will need to use something ho ptotect it like rug or towel or start it with the exhaust out of the garage.

[Owlsman]

Thanks for your comments everyone. It never occurred to me about modern cars being fitted with cats - Dhoh!

Have I just made that up about the engine running a bit rich if black deposits come out of the exhaust?

Spent nearly all morning putting my garage floor jigsaw together. It's well on the way now but it's a bit like doing the sky on a 1,000 piece proper jigsaw...…..all the pieces are the same colour.

[liammonty]

Have I just made that up about the engine running a bit rich if black deposits come out of the exhaust?

.

I think you’re confusing black ‘deposits’ with black smoke, which would indicate an overly rich mixture. However, you said that you can start the car and drive it from cold with no choke - that would indeed suggest that it is rich. I’d check the condition of the air filter as a first step. But, as others have said, I’m afraid that irrespective of the mixture, you’re going to get black marks on your nice new floor!

[philthehill]

Put a long grow bag tray under the exhaust so that when you back out the black stuff is caught by the tray.

As suggested above - if you do not need the choke the mixture is too rich. A little choke should be required for all starts from cold - otherwise why have a choke.