Here's one, but I think this simply goes to show everyone that Aerostar owners are the most observant of all Ford owners on the Ford Truck Enthusiasts Forums . My question: During the winter, I've noticed that when my Aerostar is not started and driven for 2-3 days, I see rust deposits inside the tip of the tailpipe, where it exits behind the right rear tire. I am in northern California, and not in real winter (snowbelt) conditions. I asked a friend about this at work. He told me, it is because of the winter gasoline formulas that are used now. Long story short - the gasoline, causes water condensation in the exhaust system when warming up the cold pipes. Even after driving, there is still some water condensation formed, when the hot pipes cool down, to "cold pipes". This moisture, from the gasoline by-products of combustion, causes the rusting, when exposed to chilly damp, air. Nothing in the Aerostar's operation, is any different. Only that I can look down, and notice the brown dry rust "film" inside the exhaust pipe. The exhaust system looks normal, no leaks, but I wonder what the insides of the pipes and muffler might look like? Any ideas? Is it the winter gasoline? I never have noticed this, when my Aerostar sits during the summer months, after not being driven the next day, 2, sometimes 3 days of not being started.

 

I always thought that the water from the tailpipe was all the catalytic converter since the platinum catalyst inside converts the exhaust from the engine into carbon dioxide, nitrogen, oxygen, and water which I thought was the reason for the water in the tailpipe.

 

krankshaft is correct, the catalytic conversion produces the water vapor which is then undergoes condensation in the remainder of the exhaust system, emerging as water out the tailpipe. This is also why short trips are harder on exhaust systems as the condensate collects inside the muffler. On longer trips, the exhaust system gets hot enough to keep the water vaporized and passed out the tailpipe. On a side note, some mornings I often sit behind some high dollar Asian cars with factory dual exhausts at a stoplight. When that car begins to pull away, I notice more water coming out one side as opposed to the other. Anyone else ever notice this?

 

cats are not perfect
old school chemistry
nitrous oxide+water+heat=nitric acid
nitric acid+steel alloy+heat+air=corrosion and rust

similar chemical formula for the sulfur in fuel except end result is sulfuric acid

 

Some water is produced even without a catalytic converter.
There is no nitrous oxide by the time the water is formed. Therefore there is not very much nitric acid if any formed. However, sulphuric acids are a problem. The solution is to make sure your vehicle warms up fully enough to let the entire exhaust system get hot. Short trips are hard on other parts of the car as well.

 

Water is a natural byproduct of combustion, so you will ALWAYS see water or steam coming out of the exhaust system. The catalytic converters try to complete the combustion process that the engine missed to reduce unwanted byproducts, such as unburned hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx, not N2O, which is what nitrous oxide is). When it's really cold out, and the car was just started, the exhaust system will be cold, so most steam going through it will condense to liquid water. The replacement muffler on my Aero actually has a drain hole, from which I see plenty of water dripping out when the car is just started. As the system heats up, the water vapor stays vapor longer, so you don't see it as much.

This is my guess about why a lot of cars with dual exhaust seem to have more steam or water coming out of one side. Most factory dual exhaust systems have non-symmetrical parts to reduce resonance. This usually means that the mufflers on one side is bigger, and thus will take longer to warm up, than the other side.

And trapped water will slowly rot out the mufflers from the inside. I've noticed that my Mustang has gotten noisier in the last couple of years. Its cat-back system is about 12 years old now. Short trips that don't warm up the parts are bad for everything, not just the mufflers.

 

Nitrogen oxides (NOx), a mixture of nitric oxide (NO) and nitrogen dioxide (NO2), are produced in normal engine fuel combustion. Our EPA OBD controlled engines try to run at stoichiometry or perfect air/fuel mixture levels for complete fuel combustion. In engines running at stoichiometry, combustion temperatures reach a high enough level to actually burn some of the nitrogen in the air, yielding various oxides of nitrogen...

In the air, NOx reacts readily with common organic chemicals and even ozone, to form a wide variety of toxic products, some of which may cause biological mutations. Examples of these chemicals include the nitrate radical, nitroarenes, and nitrosamines.

Motor vehicles, mainly gasoline powered passenger vehicles, product 55% of the nitrogen oxides in the US....over 25 million tons per year, and this is after 30 years of required catalytic converters
Nitrogen oxide production actually increases as an engine reaches operating temperature and the PCM goes into closed loop operation

Cats do well on unburned hydrocarbons and carbon monoxide when they are at operating temp but many cat designs actually increase the nitrogen oxide levels by chemically changing the elemental nitrogen gas in the exhaust air into nitrogen oxides

Exhaust gas recirculation systems, EGR, on vehicle engines are an attempt at controlling nitrogen oxide production

Visit Mexico City in August if one wants to see the effects of nitrogen oxide on a city