# Exhaust pipe sucking up a shirt

My hypothesis:

Imagine a cold exhaust system. You are starting the engine. With the first fuel ignition, which will probably not be the one that starts the engine, hot exhaust gas is pushed into this cold exhaust system. This hot gas initially displaces the cold air in the system, but is cooled down quickly by the cold metal. This then creates a negative pressure in the exhaust system that persists for a significant amount of time due to the slowly turning engine that’s still being cranked, allowing it to suck up the shirt.

Another hypothesis:

The caller said it happened when he was starting the engine. Suppose the engine “cranked” for a second before it “caught” and started running. During this time there are no combustion products in the cylinder. The piston moves down not because of an explosion, but because it is being pulled down by the starter motor. This will create a partial vacuum in the cylinder which will still be present when the exhaust valve opens. This will suck air back into the cylinder from the exhaust system. Once the engine fires, of course, the air flow will be in the opposite (normal) direction.

Tom and Ray didn’t ask an important question, what kind of car was it. I think I know what happened and the shirt isn’t in the exhaust system or muffler, but in the rear body work.

Imagine a hole in the muffler or tail pipe. Once the engine is started, and assuming that Mike is like most men, he reved the engine to make sure it started (and to confirm to other mention in the area that he is a man). This caused relatively high flow of exhaust gasses rough the tail pipe, according to bernoullis principles you would get a low pressure area in the area of the hole, sucking the shirt through the bodywork surrounding the tailpipe. This assumes that the car had such a configuration.

While the talk about low pressure in the engine is true, the time scale of them low pressure event is just not enough to suck in a shirt. Tom’s discussion about valve overlap was great, for a one cylinder engine at 10-20 rpm. A 4 cylinder car at idle (500 rpm/8 rps) couldn’t do what he described, even if pulling a vacuum on one cylinder all the time.

So call him back and see if the car was loud (it was a rental after all) and whether the tail pipe was surrounded by body work.

I think a prolonged period of cranking filled the exhaust system with fuel and air and when the engine finally did start, it kicked back and ran backwards for a few seconds using the fuel/air mixture in the exhaust to run on.

This happens a lot with four stroke model airplane engines that use glow plug ignitions, in fact there was one such engine that was designed so you could interchange the carburettor and exhaust pipe should you desire reverse rotation.

Incidentally, that segment, as well as the one about the VW Vanagon, were repeats from…probably 4 or 5 years ago.

Memo to Tom & Ray:
I really love listening to you guys, but…summer is over and Labor Day has passed.
It’s time to get back to work producing some new material, guys.

When a pressure wave reaches an open ended pipe part of its energy gets reflected back down as a rarefaction (suction) wave.
Similar to a musical wind instrument.
So gas can puff out followed immediately by a puff of suction.
It doesn’t have to start out as suction in the cylinder or around the exhaust valve.

Many of the above posts are possibilities.

I like all these mechanical answers. However, as an educator with over thirty years experience working with children and their realities, my best guess is that the nine year old was exploring if the blouse would fit into the exhaust, got scared when the car was turned on and instead of pulling the blouse out, shoved it into the exhaust and then said it got sucked in. Getting sucked in and getting pushed in are almost identical and only persnickety adults would see a distinction.

Here is a case where psychology not physics or auto mechanics gives the answer.

Dear Click and Clack,
the car that sucked the shirt; was it a dual exhaust system? some dual exhaust systems are designed so that a negative pressure is created at one tailpipe. air is drawn in that one and mixes with the combustion gases. this produces cleaner emissions.
Wes in CT

How this happened is a mystery. However, what the caller really needed was a solution. He should use one of the grabber tools (about 2 feet long, with metal fingers at one end, a red plastic handle and button at the other, connected by a spring wrapped around the flexible metal rod. This can be fed into the exhaust to grab the blouse and remove it. Any dead mice, frogs, or small children that were also sucked into the exhaust can be extracted by the same approach.

how about this idea: the exhaust really should have blown the blouse away rather than sucking in. Maybe the kid was mistaken–the blouse was blown down and away, maybe catching a piece on the tailpipe. But since they didn’t look around, maybe it was just an illusion (for the kid) and the blouse was blowin in the wind (sorry, bob).

Could it be as simple as a bad gasket between the exhaust manifold and the block causing airflow at that point and a vacuum at the end of the exhaust pipe?

An engine with a miss fire will often cause a vacuum at the tail pipe. I have held dollars at the tail pipe and had them sucked up and then blown out.

"An engine with a miss fire will often cause a vacuum at the tail pipe. I have held dollars at the tail pipe and had them sucked up and then blown out. "
A burned valve will do this too, used to do quick checks with a piece of note paper to see if a compression check was in order.

With the highest respect for the caller and his wonderful daughter… kids are kids. (I know because I used to be one. Honest!)

Maybe the kid dropped her blouse in a mud puddle, panicked, and tossed it in the nearest trash can.

“Where did your new blouse go?”

“Uh… the car sucked it up!”

A shirt getting sucked up an exhaust? Anyone ever heard of Occam’s Razor?

An engine is an air pump, pure and simple. Induction system in, exhaust system out. Trying to figure out some complex theory of how an exhaust pipe could suck in a shirt is all well and good, but it really stretches the imagination. A postage stamp, perhaps, but a shirt? C’mon.

Rejmember that when you’re starting an engine, and the starter motor alone is moving teh pistons up and down, those pistons being pulled down with the exhaust valves open and creating a negative pressure would be connected to the same exhaust system in which pistons are being pushed up in their exhaust strokes. creating positive pressure.

The simplest solution is the best. Kids tell stories.

Fellas, I think the answer to the “shirt up the exhaust” mystery is to be found in the behavioral rather than mechanical sciences. The child reportedly “hung her shirt” from the exhaust pipe. This is highly unlikely given that the pipe sits a mere foot at most from the ground, hardly an adequate hanging site. Also it is likely to look dirty, and no female will hang any article of clothing from a dirty pipe that will not allow ground clearance of her garment. I proved this recently. I hung my girlfriend’s sweater from the corner of the kitchen trash can. She didn’t like it. I then asked if other women might have reacted in the same way. She made it clear that this is an irrefutable truth. Therefore we can say with absolute certainty that no female will hang a garment from a low-lying dirty perch no matter where she is.

As to the volume of the shirt and the capacity of the exhaust pipe, I tried stuffing a kitchen rag into a discarded paper towel roll. It was extremely difficult to stuff it in even with the back end of a wooden spoon. Which my girlfriend, when she saw me stuffing a dishrag into a cardboard tube, used to whack me on the arm and yell, “What is the matter with you today?” I couldn’t explain to her that I was solving a mystery because by then she was no longer apt to listen to me.

My explanation rather is that, quite simply, it never happened. The little girl probably had some issue with the garment, a stain she didn’t want to show her mother, or had simply grown tired of the thing and desired a new one. The scenario I have visualized, is that she ran to the garbage can nearby, tossed the shirt in, and then went to her gullible father with this absurd story that would instantly absolve her of guilt because, as she has clearly shown, "Who would have thought something like this could happen?!?"
As to the gullability of the parent in question, I think there is overwhelming evidence that this is a man who will believe any cockamamie story or explanation anyone throws at him. After all, he does listen to Car Talk.

Kudos, however, to the young lady for apparently convincing someone (her dad?) that this happened. She has a wonderful imagination. Man, when I think of the troubles I could have stayed out of if I’d have been that creative.

Fortunately for my own daughter, now grown, she never had to try this one.