Exhaust condensation

[Mervyn Hyde]

An issue that is annoying rather than a problem. After a drive the car goes back in the garage and next morning when starting there is some sooty water expelled on to the floor until the car is warm. Condensation on the cooler evenings in the stock muffler. I could put an old mat under the car and drive off sooner I guess, but first, I am not keen on water sitting the muffler for long (rust) and second the floor gets grotty after a while. I have read that painting the system matte black will help it cool faster, and even drilling a small hole on the lower point of the muffler! I do note that some new mufflers on other cars already have this. But on 356s' ...

Are there any tricks on this one?

[David Nicholls]

G'Day Merv

Combustion of Hydrocarbons (Petrol) in the presence of Oxygen (Air) in the Combustion Chamber, produces Water Vapour (H2O) as a byproduct.
When that Water Vapour hits your cold Muffler, it changes back to water liquid, which are the drops you are seeing.
Just like in Queensland, when moist air touches the side of your cold beer, the outside of the glass becomes wet.

Porsche 356 mufflers run hot, because they are close to the engine, and stay dry on the inside.
They rust more on the outside, if not protected.
Solution, Use your Muffler, often.

Regards
David

[Dick Weiss]

As said, do more driving to eliminate internal moisture and the gray exhaust paint is correct.
However, aftermarket systems are black and it's your choice if it remains.

[Norm Miller]

Mervyn,

If you drilled the holes in the bottom they would likely drip sooty water too.
Since you are down under you could drill on the top.
Sorry, couldn't resist.

Norm

[Mervyn Hyde]

Ha ha David. Yes I well understand the principle of condensation in mufflers. Maury Swanson kindly made me up a nice one last year for the 356.

However, the design of the 356 muffler and its location is different from most cars and any condensation is going to sit in the bottom of the muffler body if not burned off. We all adopt the principle with old P cars that we will drive them often, and never on short trips. But not everyone can manage that and they can sit around for a while, or suffer the indignity of an occasional trip to the shops for the milk (I know of a Carrera 2 that did this). Yes Norm, we lived in NY and St Louis for several years and I never really convinced many friends there about the Down Under Relativity Theory.

However, David you may have answered my question in part by suggesting that the condensation is NOT from accumulated water already in the muffler after its last run (as in some other cars), but only from initial contact with the cold muffler surface, regardless of how far it was driven last time? In other words such condensation will always occur in our relatively humid climate, no matter how much your drive the car?

[John Brooks]

It's probably not trapped water, it forms on start. The water will form as long as the muffler tempertature is below the local DEW POINT. If the muffler was warm then the drops will not form. If it's really irritating put a spring clamp 50w light bulb on the muffler / tail pipe and plug it in. It will keep the muffler warm prior to start.
Years ago we used to put one bulb in a square metal cake pan, with a broom handle on it. The pan with a bulb was slid on the floor under the engine to keep the oil warm in the cold winters for morning starts,

[Mervyn Hyde]

Thanks John and David. I am pretty sure that water is not accumulating in the barrel of the muffler after shut off, as you describe. I will just leave the mat in place behind the car to catch the dirty water.

[Larry Coreth]

Guys,
To prove to yourselves that no water will be retained in the muffler once the motor is at operating temperature sight your optical pyrometer on the hot muffler (not on the center where the insolated section is, assuming a stock system) but on the ends. Guaranteed the temp. will be well above 212°F !! Well above, thus ensuring and any water is now steam !! Also assuming you drove the car long enough before shutting it down all the condensed water from startup is now been heated to steam again and expelled !!

BTW, the local dew is irrelevant to the condensing of the steam in the exhaust. It is all about the steam hitting the cooler steel of the muffler, absorbing the heat thus allowing the steam to turn into water. The only influence the local dew point has on the motor is that as the dew point rises the air density decreases thus leaning out the mixture and of course more water vapor is ingested too, ending up as steam in the exhaust.

One more thing if you want to minimize the carbon (the dirt) mixed in with the start up condensation go out and give your car an "Italian Tune UP" occasionally and blow out all that accumulated carbon in the exhaust system, the heat will help too. Secondly make sure the motor is not running too rich. this will coke up the exhaust system badly which will only make the situation worse.