Seafoam shock treatment

One of the things that has concerned me about the boat’s motor is the very low compression it has. When I tested it right after I bought it, each of the cylinders was reaching only about 80 psi, when it should be up about 120 psi. Granted this is an old boat, and who knows how it was cared for? The important thing is that each of the cylinders is close to each other in compression.

When I was researching boat repairs, I came across many different YouTube videos about shocking the engine with Seafoam to remove carbon and unstick the rings. Since it is a detergent it would also clean any other internal components.

I have a two-cycle engine, so the recipe is really simple. Get a small gas can that will hold a couple of gallons. Put a gallon of good gas in it. Mix in an appropriate amount of two-cycle oil. Add one whole 16 oz can of Seafoam. Mix thoroughly.

Place the engine’s fuel line into the gas can, and start it up. In my case I have an internal fuel tank, so I would need to disconnect the hose from the boat in order to put it in the fuel can.

Let the boat run at idle or low throttle for 10 to 15 minutes. It will smoke. A lot. Blue smoke good, white smoke bad. After the 15-minute run, let it set for 10 to 15 minutes. this stage is to allow the Seafoam to dissolve carbon on the rings and internal components.

Start up and let it run another 10 to 15 minutes. Repeat the shutdown for 10 to 15 minutes. Keep doing this until you run out of gas.

I keep some gas for the lawnmower out in the shed. It is kept in sealed container with some Sta-bil fuel stabilizer. I’m one of those people who fills up 8 five-gallon gas cans once a year. I try to keep enough fuel on hand to run our generator for several days if the power goes out.

A quick pour of about a gallon into a 2 gallon gas can and a short walk to the boat and I was ready to get started.

I keep boat 2-cycle oil in the rear hold, next to the batteries and fuel tank. I use a marked container that specifies amount of oil per amount of fuel being added. I measured it out and into the gas can it went. Then I put just a little more oil, just in case.

With the gas can sealed up, shake shake shake. Interestingly, the gas can became pressurized when I did this. When I opened the can, it released pressure in a surprise toot. I do that sometimes, myself. I’m guessing the gas had some dissolved gasses in it. If I recall correctly, fuel pumps add some air to the fuel during pumping.

Ok, I need to put the fuel line into the gas can. To do that, I have to get the line off the boat. Oops, I forgot to get a screwdriver for the clamp.

It was a short trip to the garage to get a flat-blade screwdriver. I had the fuel line off the boat and into the gas can in a couple of minutes. I gave the priming bulb a few squeezes to get the fuel up into the carburetors. It took a few more squeezes than I remember to get them filled up and primed. Then I remembered that the fuel system, including the entire fuel line was empty. Of course it will take a few more squeezes.

The boat has run once already this year, so it should start right up, right? I hooked up water to the water intakes and turned the key. Crank, Crank, Crank. No start. <insert big heavy sign> Squeeze the fuel bulb again, and it was still pretty tight. Crank Crank, Signs of life. Crank again…and it started. The idle was a little rough, but I didn’t have to throttle it to keep it running. It smoothed out quickly and I let it warm up for a few minutes, then shut it off.

Next a whole can of Seafoam went in the gas can. Shake Shake Shake. The fuel line went back into the can. I was very curious what would happen next.

I turned the key and it started right up. I’m not sure it did a whole revolution before it started.

At first it was putting out normal smoke, but once the Seafoam shock got into the carburetors, it put out quite a bit of smoke. I expected that. I let it run 15 minutes, then rested it for 15 minutes. It started right up again.

It smoked quite a bit more this time! Once again, I let it run 15 minutes, then rested it for 15 minutes.

The third start smoked even more. I mean, yeah, that was a lot of smoke. Good news it was always a blue-tinged color, so it was oil, Seafoam, and whatever carbon was burning out. Between the noise and the smoke, I’m surprised a neighbor didn’t come over to find out what what going on or to help with the activity.

There was just enough fuel to run it three times. It started to sputter a bit on round 3, so I positioned the can at an angle and got the fuel line into a spot to get what remained in it. It ran out a couple of minutes later, so that was that.

So, did it help? When I checked compression last year, it came back with 72 82 79 75 80 73 for each of the cylinders. That’s in PSI. I have since run about 30 gallons of fuel through it with Seafoam at a normal concentration and have rebuilt the carburetors. Perhaps that has helped clean it up a bit.

I should have taken the time to check the compression before the Seafoam shock treatment, just to have a better before and after. Oh well. I checked after the fuel ran out. It is a remarkably consistent 70, 80, 80, 80, 80, 80. So, better? Maybe. The top cylinder is a little low, though, but still within 10 PSI. I checked it twice with the same results.

While I had the spark plugs out, I inspected them. They had a little carbon on them, but not bad. I scraped/rubbed off the carbon and wiped them down a bit. Back into the motor they went.

What I do know is that this old Mercury is tired and due for a rebuild. I’m not sure I’m going to be the guy doing that as it will cost about as much as I paid for the entire boat to have somebody do it. It will be a whole lot of time and effort for me to do it. I’d need a shop with a hoist and work bench, and about $500 of parts. All that, and several weekends dedicated to it. I’m not sure the boat is worth it. Then again, it would be a learning experience. I understand that when these motors are in good shape your boat will fly.

In any case, I’m looking forward to putting this thing back in the water. I’m very curious if the combination of fresh fuel and the Seafoam shock treatment has made a difference.