Fuel additives

I have a Tollycraft 34 that has two 100 gal tanks. What is a good additive to use?

 

What are you trying to do?

Sta-Bil is the stuff I use, but you have to decide what you're looking to do, before you ask for a product recommendation.

 

I bought the boat about 4 months ago and had a lot of work done including emptying both tanks, I filled both tanks back up with about 90 gallons each about 3 months ago. I've been having engine problems and haven't been able to run the boat much. I just replaced both primary fuel filter/water separators and both small fuel filters near the carburetors and hopefully solved the stalling issues, i will test drive it tomorrow or Saturday. Im wondering if I should use a fuel additive to help the gas last longer and the engines run better. I'm using the highest octane fuel available. I'm new to boating and I'm looking for suggestions.
Thanks Par!
Dan

 

The whole fuel stabilizing thing is fascinating. I have never used fuel stabilizer.

I do have fuel shut offs in the boat and I do run the carburetor dry before storing the boat for the winter. Leaving fuel in a carburetor/fuel lines and filter(s) is a recipe for problems. If an engine is fuel injected I don't worry about it at all. I have an older (1985) Nissan 300zx that I've stored for as long as 4 years. The fuel system is sealed up. I start the engine once a month or so just to keep things lubricated. Never had a fuel related problem.

All that said, I have good friends who are ASE certified master mechanics. These guys know their stuff and some of them swear by fuel stabilizer. Go figure. I think there are more ways than one to approach this.

I'll share a story about bad gas. back when I was restoring my boat I realized after the boat had been in the yard for the better part of 10 years that I probably should get the old gas out of the tanks. I ended up with about 50 gallons of a liquid that was gas but now smelled very much like turpentine. I called around to anyone I could think of. No one anywhere would take this old gas. What to do?
Since I didn't want to just pour it out onto the ground I figured I'd try mixing a few gallons of this mystery liquid into the fuel in my old Chevrolet Suburban. A 20% mix seemed to run fine, so next fill up I tried a little more, then more and then even more. I reached the tipping point at about 50%. WIth a 50% mix of turpentine (or whatever the old gas had morphed into) and fresh gas the truck ran fine but was a bear to start, especially if it was a little chilly in the morning.
I realized quickly that the old gas was difficult to light off when the engine was cold. The engine would fire, but not run. After a couple of minutes of this enough heat would build up in the cylinders to get her running roughly. After another few minutes she would smooth out. The only other hassle was that I had to keep clearing the codes from the ECM since the check engine light kept coming on because of the cold starting misfires.
In the end I used up the old fuel. added a little Sea Foam to clean things up and filled my truck up with all fresh fuel. That was 5 years or so ago and I've never had any issues with the injection system.
The reason I wrote all this was to demonstrate that even ancient fuel, mixed with fresh can burn in an engine.
You have 3 month old fuel which should be fine. You say you're having engine problems but are you sure they are fuel system related? Depending on the compression ratio of your engine(s), you may or may not need premium fuel. If you determine that your carburetors are the problem, I would suggest a thorough cleaning and rebuilding of the carburetor(s) as a start. You really need some with some knowledge to diagnose the problem, otherwise you are just guessing and probably wasting money "fixing" things that don't need to be fixed.
Weather or not you use stabilizer is a choice only you can make but as I said I have had no fuel related issues in any of my vehicles and have never used it. But I never leave fuel in a carburetor during storage.

 

A hot engine certainly will run on old fuel that the more volatile part has evaporated off. I seem to recall some outboards were warranted to run on kerosene, but only after start and warm up with gasoline. Might have been Tohatsu.

 

Through time i have used several different types of fuel additives, IMO the best one is called Algae-X. Its mostly marketed to eliminate the algae problem in diesel engines as well as to clean the fuel system, however it can also be used to clean gas fuel systems and to preserve the fuel after you have winterized the engines to preserve gas from going bad.

Now days thats the only fuel additive i use for diesel and gas inboard or outboards.

 

Again, without knowing more of what you're doing or desire and what you have (gas, diesel, chipmunks in a cage, etc.) it's tough to offer anything.

I use stabilizers all the time and Sta-Bil is the common choice. With gas, particularly ethanol and other additives tend to drop out and/or accumulate moisture over time. A hot engine will eat most anything, but try to starting a worn out, stone cold, missing half of it's compression puppy, with 3 month old fuel, will just piss you off.

I could offer a lot of chemical reasons for it, or you can just take my word and pour the appropriate amount of Sta-Bil in your tanks and maybe a little fresh fuel on top, to help mix it in. Trust me, there's lots of frugal skippers that have been swearing by this stuff for decades. Us cheap basterds will pour really old fuel (read years) into new, add some Sta-Bil and not even think about tossing it away, just because it's old.

 

Thank you all for your help and advice. I've never worried about fuel additives before but I didn't own a 42 year old boat with two gasoline engines and 200 gallons of gas on board. The more people I talk to and the more I read about ethanol in the gas and water build up in the tank I'm taking fuel additives more seriously. Just trying to find out what you guys with some experience are doing? Thanks again!

 

Water separator traps are de riguer for any large fuel tanks in boats. In a place that is easy to check them. If in doubt fit two of them in series. Drain as needed. It is remarkable how much condensation can form, and if it gets to the carbs, a real nuisance. Worse if fuel injection. Fuel pick-ups at the rear of fuel tanks may only pick up a small amount until the boat is gunned and the nose rises, causing water to pool at the pick-up.

 

The gas will have water from the ethanol , which literally sucks moisture it out of the air .

The ethanol will also dissolve old fuel lines , the inside of fuel pumps and older gaskets in a carb.

Massive work to replace it all but needed.Hopefully the tanks are metal, not GRP.

The current operating techniques is a reversal of what was done in a bygone non bio-garbage era.

Return to your slip with the minimum amount of fuel in the tank that you dare.

Fill Fuel to operate when you go out , and keep the tank as empty as you can.

Its not in every state but non ethanol fuel is at some marinas.

Aviation fuel is pricey , and has to be drum carried , but is the best gas for good operation.

High octane is a pure and total waste of your money , unless your engine is a modern twin turbo that demands it.

Purchase a carb rebuild kit for each engine to get the new bio junk resisting gaskets

 

Anecdotal:

For many years I used to deny that gasoline ages. There is a 1980 Porsche 928 in my garage with very, very old fuel. It has been standing there for at least 18 years now and when I felt the need to move it I put a battery in, turned the key and the big V8 came to life.
But in the beginning of 2015 things went wrong: the electric fuel pump refused to turn, so I bought a new one. The engine started but died as soon as I touched the accelerator.
A few months later the recently installed fuel pump also stopped working, so I took it out and drained the fuel tank, expecting water or sediment. But there was only fuel, albeit dark brown, oily and smelling like month balls.

I got the pump going again by filling it with acetone. After half an hour it reluctantly started to work again, so I installed it and partly filled the tank with a 50% mix of the brown goo and fresh gasoline. The engine started the first time but refused to do more than 1500 rpm no matter how fast or slow I put my foot down.
Only after I poured several bottles of acetone in the fuel tank, things started to improve and the car was able to leave the garage under its own power.

Conclusion: gasoline turns into something else after approx. 16 years, but the addition of enough acetone can (at least temporarily) rejuvenate it.

 

You tried everything except lemon essence ! I'm not sure what gasoline turns into after sitting around that long. Smells a bit like mineral turpentine to me.

 

Chemically a lot of things are happening and it also depends on the way gas is stored, but generally a number of the lighter volatile elements boil off, become contaminated or disassembled, because of the presence of other elements. Sun light can really speed this up, as can air.

Acetone wouldn't be my choice. I'd first turn to isopropyl alcohol or better yet a fuel drier. Modern engines (automotive) will have a charcoal canister which will help tremendously, as does modern fuel injection, but the converted and/or missing volatile elements will still cause the engine to run like crap. The easy way is to dramatically dilute the old mix. The EPA recommends 5:1, which I've found way more than necessary. The problem with this is you'll likely still be drawing moisture through the system without iso or metho driers. Additionally, the physical remains of other additives will likely cause issues too, so pump out at least 50% of the fuel and add as much back in with a fuel stabilizer. Most of the common fuel stabilizers will hold fuel fresh for a year or more. Increasing the percentage of stabilizer will proportionality improve this up to about 2 years.

 

what about acetone etc dissolving the non ethanol resistant components in the fuel system?
if its a 2 valve 928 it is happy with leaded fuel so avgas would be perfect

 

This is a 928 with Bosch continuous injection (K-Jetronic), one injector for each cylinder and a 9th in the intake plenum that slowly closes after approx. one minute. All plumbing is metal, but there may be needle valves with neoprene seats in a giant device that distributes the fuel.

The car is useless to me, roads on this island are pretty bad except for the main one and I need several guys to lift the car a bit when going on the ferry because of the small ground clearance.
In spring I will thoroughly clean it and take some serious action to sell it to a car collector.