I recently purchased a boat. It sat for a couple of years and the fuel in both tanks was stale. I have spent the last couple of months using up the fuel in the engines and onboard generator (about 140 gallons worth). I'm about to put in fresh fuel and am curious what would be the best additive to the tanks to clean up any varnish or buildup that has occurred in the engines' fuel systems due to using up the old fuel.

Suggestions?

Sea Foam

I've heard good about Seafoam also. I think MP has a combustion chamber cleaner & it is reportedly extremely good. If it comes in a liquid as opposed to a spray I would choose it before even Seafoam

How about a half gallon of methanol lacquer thinner in a fresh tank of gas, you have to use up the gas, though.

R.

about fifteen years ago i did an experiment at home where i soaked 1994 5.9 v8 pistons for several weeks to see which liquid would remove the carbon deposits the fastest

LiquiMoly Ventril Sauber
did better than Chevron Techron, Seafoam or Chrysler ATF+2

i later learned that in German
"Ventril Sauber" means "valve cleaner"

http://www.liqui-moly.de/liquimoly/produktdb.nsf/id/en_1014.html?Opendocument&land=DE

BMW and VW dealerships stock this product

since that time Chevron has changed the formulation of Techron and now calls it Techron Plus

with the new video borescopes costing less than $200 i guess one could do home experiments to see which fuel additive best cleans off deposits on intake valves

i have wondered what a couple weeks of running E85 would do to intake valve deposits

I personally have never seen any independent proof that any product will really "drive our engines clean". Has anyone else seen any real world tests?

As to combustion chamber and valve cleaning, there are a number of very good products for that. But they aren't diluted in the fuel. They are poured in the intake tract while running or sprayed into the cylinder directly through the spark plug hole.

Combustion chamber cleaner or upper cylinder cleaner are a couple of names. GM has it as do most outboard motor shops.

It does a very good job.

I agree with Dave. I ain't done it but I've heard that dribbling water slowly into the carb at a fast idle will do it & do it very well

An "Old Timer" showed me the water method. As long as you keep the idle up and slowly spray water into the carb, you will see black smoke come out of the exhaust.

Water will work.....eventually. It takes a good while to do a complete job. The chemicals just speed the time up. They don't necessarily do a better job. Just a whole lot quicker.

Chrysler Combustion Chamber Cleaner Part # 04318001AB
seems to be a foam made with both water and a solvent.

There used to be a member here on Moparts that tested multiple fuel injector cleaners for Chrysler to find the one they would sell as their officially labelled one.
Perhaps if he sees this he will chip in.

What do the spray cans for internal carbon deposit removal sold by GM, Toyota and Ford look and perform like?

Water sprayed into the intakes is said to work by first being absorbed by the spongey carbon deposits' many interior holes. Then this absorbed liquid water flashes to steam from the heat of combustion. the repeated expansion of the steam breaks up the carbon.

I did an experiment several years ago where i added a second PCV valve to a 1995 360 V8 and used this to suck the air conditioner drain water from the lower passenger side outlet nto the intake manifold through the test port on the driver's side intake manifold. The engine ran ok with less pinging, but there was gurggling noise that could be heard at idle through the air vents. MPG in city driving went down noticeably.

Yes, the Mopar CCC is a foam. You slowly spray it in the carb/TB, while keeping the revs at a fast idle. When the can is gone, shut off the engine and let it soak. When you start it up later, there will be a smoke show. It does work.

Y4 challenger asked about something to clean his fuel system, not his combustion chambers.

Seafoam is what I would dump in my fresh straight gas I got at the marina. Just like what was suggested. In other words non ethanol gasoline, hopefully available at your local marina.

Then I would dump a second can of seafoam in your motor oil and go have fun with your boat.

When I bought my pickup, I used sea foam. That thing belched vapor for about a half hour before it stopped. Later I had to take the heads off anyway. Was it ever clean in there. Wish I'd have taken pics.
So yes, Sea foam!

You are right, the title asks one question and the post itself asks another.

As to the combustion chamber cleaner, I have used several different brands. Most of them look, act, and even smell the same. Kinda white, foamy, slick feeling and water soluable.

I use it to clean carbs and fuel related items mostly. Works great and doesn't hurt the coating on aluminum. Usually the spray from OMC and the pour can from GM are the easiest to find. But it is a lot more expensive than regular carb cleaner.

Combustion Chamber Cleaner was the ONLY product OMC (Evinrude/Johnson) recommended to clean carbs and related components.

What does using something like Seafoam down the PCV line do to the convertors? Will the sudden rush of deposits clog them up?

Way back in the late 70's I saw a guy with a 66 Nova with a big block pour trans. fluid into his carb. with the rpm's up and I asked him why he did that and he said in cleans out the combustion chambers. Ever try that one?