[I am Confused]

Usually I'll pour 8 ounces of Seafoam in the crankcase 100 miles before I expect to change the engine oil, and I'll do the "smoke show" routine pouring an entire can via brake booster vacuum after oil change.

I've been told that's a waste of money, or that it's harmful. I'll say based on my experience that I've never ruined an engine doing this, and my gas mileage is always phenomenal for what I expect from a four banger like this.

Two cans of Seafoam is the best $16 of DIY maintenance I spend on my car.

 

[I am Confused]

Correct. Before oil change.

Considering the magic little can cleans carbon buildup on cylinder head, any unburned excess is dumped onto oil pan, so that would be bad news long term for the engine.

 

[I am Confused]

{bolded}

As a quick sanity check I just googled " Seafoam twice in a row" and found some other folks that did this and commented the same minimal smoke the second application. :dunno:

I think the "smoke show" is mostly carbon buildup burning off via exhaust, so I wouldn't expect a spectacular show the second time around unless some driving time passed between treatments.

 

[I am Confused]

And your "smoke show" is caused by what, exactly, in your opinion?

You think the smoke in the exhaust pipe is an evidence of cleaned carbon deposits on the cylinder head?

This might seem anecdotal to you, but before the Honda I have now I used to own a 2004 Accord with SULEV I4 engine which was burning one quart of oil every 1,500 miles on average. I tried a list of things suggested in this website to try slowing it down, but all failed.

I did the Seafoam cylinder head soaking procedure; remove spark plugs, pour some Seafoam into each plug hole, let it sit for 8 hours, crank, pour some more into each plug hole, let it sit 8 hours again.

Once I finished the soaking procedure and took it for a spin, the car would not stop smoking for a short while. In fact, the exhaust had a strong hint of Seafoam for some time even after changing the oil. The oil stopped burning as fast once I did this, but it still burned.


So based on my experience, yes Seafoam is mostly burning off carbon buildup when the car smokes. Or in the case of soaking procedure, it's burning off old engine oil stuck in piston rings.

 

[I am Confused]

According to their sites' explanations, Seafoam is apparently highly refined petroleum whereas B12 is a mix of solvents. Both engineered to do the same job.

Take it for what its worth I guess.

 

[I am Confused]

Yeah... I mean, personally I'd stick with what you think has worked best for you.

I've used Seafoam for years with positive results for the most.

Sadly, it didn't help much with the previous Accord I owned, but that was mostly and very likely due to previous owner neglect. Nothing short of an overhaul fixes that.