Weird exhaust shape

I saw a car at the Quickie-Mart yesterday with weird-looking exhaust smoke. I’ve seen it before (years ago) but forget what it means. The exhaust was puffing every few seconds a perfect circle of smoke(exhaust), as if it was someone blowing smoke rings with cigarette smoke. What does it indicate? Rocketman

Was this an Alfa Romeo y Julieta by any chance ?

Nope . . it was an 80s Ford pickup . . . running kinda rough. Rocketman

I wouldn’t swear to it, but I seem to remember this problem being diagnosed as a failing CAT, it was a long time ago but my generally unreliable memory keeps coming back with that answer.

Alternatively the guy may have fitted a smoke ring generator, and yes, they do exist.

Cool! How can I get one?

I don’t think that it was fitted with any trick set-up. The pickup was an older one, kind of beat-up, running a little rough. It didn’t appear to have any after-market exhaust on it. Rocketman

'fraid I’ve no idea, you get one free with 2 stroke engines but the only 4 stroke unit I’ve seen in the flesh was homemade. If your engine’s in good shape you will need some form of oil injection (I think it’s cooking oil) for the exhaust system plus an exhaust blower. Alternatively you could just buy a car with no piston rings remaining and experiment.

Some dedicated Googling might trun something up.

My guess is it is running on all 3 of 4 cylinders. That one is causing the smoke and it likely will only occur at idle and at a specific temperature and RPM.

Ah, there you go. It is a little-known experimental engine diagnosis system that was tried by Ford and installed on a few vehicles. The diameter and frequency of the rings can be read to yield a trouble code. It did not work very well and the vehicles were supposed to be all retained by Ford. Some apparently slipped through the cracks and were left in the hands of private owners.

I don’t have an answer but this reminds me of something similar I once saw. On a school field trip around 1974 the school bus in front of the one I was on blew a perfect smoke ring as it started from a stop (I just happened to be looking in the right place at the right time). There was nothing special about the bus in question–it was a gasoline engine International and I’m positive it didn’t contain a catalytic converter (or a smoke ring generator). The bus wasn’t old and probably was running very well. Also, all of the district’s buses were stick shift. Any ideas? I’ve since not seen another vehicle blow a smoke ring and have been mildly curious over the years as to what caused this.

ha ha ha that is a good one!! in light of the recent sophomoric comments on here lately, i little humor goes a long way!

You might be able to find someone with enough aerodynamic, pressure, wave,… theory to model this phenomenon. The fact is that what goes on in an exhaust system would dazzle most of us.