Can Seafoam Motor Treatment Clean an Engine’s Combustion Chamber?

Seafoam is the brand name of a product that’s been around for ages. It began as an engine treatment designed to remedy fuel-related problems and, early on, gearheads found that Seafoam could resolve pesky engine issues like minor misfires, idle hiccups, and noisy valvetrains.

Nowadays, Seafoam has expanded into a line of engine oil/fuel additives, but this article is going to focus on the original Seafoam Motor Treatment.

And it’s not just for automobiles, Seafoam says this treatment works for pretty much anything with an internal combustion engine—motorcycles, boats, lawn mowers, snow throwers, etc.

So, when my humble AMC 258 inline six developed a (very) slight miss at idle, I thought some Seafoam may help.

But first! I checked the condition/adjustment of a few more important things: the timing, the plugs and ignition wires, and the Carter BBD carburetor.

Everything looked A-OK, so I proceeded with the Seafoam.

This isn’t the first time this particular engine had been treated with Seafoam either. It got a taste about a decade ago when I was reviving the vehicle after a long dormant period. It worked well in that scenario, so I was curious to see if it’d perform the same magic again.

On its website, Seafoam lists a couple of uses for its Motor Treatment: When poured in the fuel tank, it can clean jets/injectors and stabilize gas. When added to engine or crankcase oil, it can clean moving parts and dissolve deposits.

But I’m using it to clean the combustion chamber, so the Seafoam is going right down the carburetor’s throat and into the intake manifold, on its way to each cylinder.

Despite the word “foam” in its name, Seafoam Motor Treatment is a liquid with about the same viscosity as water, so it’s easy to pour. (Seafoam also makes a spray can.)

Using Seafoam Motor Treatment

I pop the hood, take the air cleaner cover off, and start the engine. Once the motor’s warmed up and idling, I begin carefully pouring the Seafoam directly out of the can and into the carburetor—yes, the engine will stumble, that’s normal. But I’m careful to pour it sparingly, as too much will cause the engine to stall. Let’s say that again:

Pour the Seafoam sparingly, a little bit at a time.

On the Carter, the shaft that holds the choke’s butterfly valve is right inside the carb throat, so I pour the Seafoam onto the shaft to further break up the droplets of liquid.

Once I poured in about half the bottle, I cut the engine. Then I let the engine sit (non-running) for 15ish minutes. Seafoam says that’s when the treatment really works its magic, cleaning the piston heads and creeping up to the valves.

Since I had half the bottle left, I just dumped the remaining Seafoam into the gas tank. While I’m not sure it’ll do much, it keeps a half-empty can off my already-crowded shelf of random half-empty cans of fluids, oils, and lubes.

After a sandwich (or 15 minutes) later, I restarted the engine. It fired up with no problems and a thick puff of smoke from the tailpipe heralded evidence of the Seafoam’s cleansing action.

The motor settled into a nice idle and was humming like a sewing machine.

But I’m not done yet. Per Seafoam’s guidance, you’re supposed to take the vehicle on a 10- to 20-mile shakedown run to fully purge the gunk from your combustion chambers.

On the road and at speed, there were no issues whatsoever. No surprise there, as the engine was running pretty well beforehand anyway, I just really wanted the idle to be rock solid again.

And it was. At an assortment of stoplights, the idle was nice and smooth. Though the vehicle doesn’t have a tachometer, my ears and hands served as my primary idle test instruments—yet there were no hiccups, stutters, or odd vibrations, just a happy and content AMC 258.

Closing Thoughts

While it’s not a cure-all for significant engine sputters, a rough idle, or hesitation, Seafoam can help remedy some pesky minor engine issues. And it’s absolutely worth mentioning again that I checked several things (timing, spark, carb) before proceeding with the application.

But after my few experiences with Seafoam Motor Treatment, particularly those involving the engine in this article, I’ll happily turn to it again if the need arises.