Running a two stroke from a large static tank? How to deal with mix?

[Franziska]

Hi,



how would you run a set of two two stroke engines from a large built in 50 gallon tank, which obviously can't get easily be shaken by hand to get the 1:50 mixed properly before start?

Ideal would be to run directly from the large reservoir as it avoids situations where a day tank would run empty when you are in a bad weather situation.



Is there some (reasonably priced) equipment for this which can "inject" the oil from a separate tank as needed? Other solutions?

If you suggest equipment I appreciate a link to suitable manufacturers.



Please don't suggest getting a 4stroke instead 🙂

[thinwater]

Add the oil before your start filling. The filling will mix it in. You could add it in several increments if you wanted to.



Who shakes even a 5-gallon can?

[Franziska]

Thanks. We are talking of fifty gallon. Occasionally this tank might sit for a number of weeks unused, which might lead to separation of oil and petrol. You can't simply stir it then, hence the question.


The external system should essentially create the Premix on the go, injecting the oil into the fuel line between tank and engine.

We usually give the small outboard tank on our dinghy a short shake before starting up.

Still, I'm not talking about the dinghy out boards above..

[Cheechako]

Originally Posted by Franziska

Thanks. We are talking of fifty gallon. Occasionally this tank might sit for a number of weeks unused, which might lead to separation of oil and petrol. You can't simply stir it then, hence the question.


The external system should essentially create the Premix on the go, injecting the oil into the fuel line between tank and engine.

We usually give the small outboard tank on our dinghy a short shake before starting up.

Still, I'm not talking about the dinghy out boards above..

I would say the gas in your carbureator will get you out of the anchorage/marina and by then the boat motion has mixed the 50 gallon tank adequately. Gas powered powerboats with one or 2 engines just start and go and have done so for probably 75 years. I think you are overthinking this.

A boat in a slip or at anchor also has boat motion/action daily.

[OutOfControl]

Originally Posted by Cheechako

I would say the gas in your carbureator will get you out of the anchorage/marina and by then the boat motion has mixed the 50 gallon tank adequately. Gas powered powerboats with one or 2 engines just start and go and have done so for probably 75 years. I think you are overthinking this.

A boat in a slip or at anchor also has boat motion/action daily.

I have run two strokes for many years and Cheechako is right. The boats motion should be more than enough to keep the fuel properly mixed.

[Nicholson58]

[QUOTE=Franziska;3889276]Thanks. We are talking of fifty gallon. Occasionally this tank might sit for a number of weeks unused, which might lead to separation of oil and petrol. You can't simply stir it then, hence the question.


The external system should essentially create the Premix on the go, injecting the oil into the fuel line between tank and engine.

We usually give the small outboard tank on our dinghy a short shake before starting up.

Still, I'm not talking about the dinghy out boards above..[/QUOTE


The 2-st oil is totally miscible in gasoline. It will never settle out. It’s like salt dissolved in water. Mix the oil in the fuel jerrycan and transfer to the 50 gallon or add oil to the 50 and top with gasoline. No problem, don’t overthink this.

BTW, I recommend an in line fuel filter with a water separation and drain bowl.

[Don C L]

Probably a good idea to add something like Sta-Bil to treat the gas since it will likely be sitting for long periods of time. I have only have 2 6-gallon tanks and it takes me forever to burn through it all.

[Lepke]

There are various injection systems for injecting oil or water. Check industrial supply. Not Cheap.

[Munoz]

If you really insist on going the oil injection route Suzuki built a series of oil-injected two strokes in the late 80's. Might be cheaper/easier to find a couple of those 2nd hand than installing a dedicated oil mixing system.

If it where me, I'd just put the oil in the main tank as suggested., you could always rock the boat a bit or find another way to mix it if you're really paranoid.......

[Franziska]

Originally Posted by Munoz

If you really insist on going the oil injection route Suzuki built a series of oil-injected two strokes in the late 80's. Might be cheaper/easier to find a couple of those 2nd hand than installing a dedicated oil mixing system.

If it where me, I'd just put the oil in the main tank as suggested., you could always rock the boat a bit or find another way to mix it if you're really paranoid.......

Rocking the boat is not very successful on a multihull 🙂
As to the Suzuki option, we could get brand new Tohatsu 9.8 for a reasonable price, so no need to buy old motors.

[catsketcher]

Seems like a strange system - did you get rid of your twin 9.9 four strokes? If it was me I would not mix the two stroke. I found that leaving premix for a while caused the fuel to produce strange products - a varnish like thing in carbys is the main one.
Maybe use a 20 litre plastic fuel tank for each outboard. Use a pump to pull fuel from the large tank to fill them, you could have a fuel flow meter on an electric pump and add the correct amount of oil (I wouldn't, I would just check the sides of the small tank and work out how much went in and do the maths). I don't have large tanks on my 38ft cat. I still just use the two 20 litre fuel tanks and fill them with jerry cans. I may go months without refueling but using a two stroke will take more fuel - so maybe an electric pump to fill the smaller in use tanks would be good - but why 2 stroke? The Yammies four stroke 9.9s are so good. I have never had an issue with running out of fuel (say in bad weather) in 24 years of owning the boat - so using the small tanks would be a good first step . Easy to check fuel levels too.

[Franziska]

Originally Posted by catsketcher

Seems like a strange system - did you get rid of your twin 9.9 four strokes? If it was me I would not mix the two stroke. I found that leaving premix for a while caused the fuel to produce strange products - a varnish like thing in carbys is the main one.
Maybe use a 20 litre plastic fuel tank for each outboard. Use a pump to pull fuel from the large tank to fill them, you could have a fuel flow meter on an electric pump and add the correct amount of oil (I wouldn't, I would just check the sides of the small tank and work out how much went in and do the maths). I don't have large tanks on my 38ft cat. I still just use the two 20 litre fuel tanks and fill them with jerry cans. I may go months without refueling but using a two stroke will take more fuel - so maybe an electric pump to fill the smaller in use tanks would be good - but why 2 stroke? The Yammies four stroke 9.9s are so good. I have never had an issue with running out of fuel (say in bad weather) in 24 years of owning the boat - so using the small tanks would be a good first step . Easy to check fuel levels too.

Just checking for now.



We might have a chance to get two new Tohatsu 9.8 two strokes. Hailed by many as one of the most robust engines around. Simpler than the Yamahas, easier to fix or get fixed in remote places.



I just learned that it's very difficult to get parts like the CDI unit for the Yamahas in some non first World countries. Takes a lot of money and even more time to get such.

Thankfully we had a second engine (in some locations you need to motor a few miles before you can sail).

The other is that mechanics in this type of places are much more familiar with the less complicated two strokes.





Much lighter than the Yamahas.

We could even get a third one for the dinghy. So three identical engines on the boat. One fails and you still would have the dinghy one which you can mount in its place.



Still there is the inconvenience with the mix.

Regarding letting premix sit, that's exactly what I would like to avoid. Have the main tank as normal and mix in the oil thereafter.



Maybe you are right and we need some sort of daytank for each of the two engines. The stupid thing is the fuel transfer would nessecitate it to install a big pipe to be reasonable fast.



No saying we go down the two stroke route, but its worth a thought.

[CaptainRivet]

Originally Posted by Franziska

Just checking for now.



We might have a chance to get two new Tohatsu 9.8 two strokes. Hailed by many as one of the most robust engines around. Simpler than the Yamahas, easier to fix or get fixed in remote places.



I just learned that it's very difficult to get parts like the CDI unit for the Yamahas in some non first World countries. Takes a lot of money and even more time to get such.

Thankfully we had a second engine (in some locations you need to motor a few miles before you can sail).

The other is that mechanics in this type of places are much more familiar with the less complicated two strokes.





Much lighter than the Yamahas.

We could even get a third one for the dinghy. So three identical engines on the boat. One fails and you still would have the dinghy one which you can mount in its place.



Still there is the inconvenience with the mix.

Regarding letting premix sit, that's exactly what I would like to avoid. Have the main tank as normal and mix in the oil thereafter.



Maybe you are right and we need some sort of daytank for each of the two engines. The stupid thing is the fuel transfer would nessecitate it to install a big pipe to be reasonable fast.



No saying we go down the two stroke route, but its worth a thought.

Plus they are so light you can even check them in as normal luggage on a plane.

[Jim Cate]

Do you have any authoritative info that says the mix will separate whilst sitting? I don't know what would actually cause such an action.

But rather than elaborate tankage mods to accommodate the problem if it is real, how about adding a small circulating pump in the tank to keep it stirred up? Seems a lot simpler to me!

Jim

[Franziska]

Originally Posted by Jim Cate

Do you have any authoritative info that says the mix will separate whilst sitting? I don't know what would actually cause such an action.

But rather than elaborate tankage mods to accommodate the problem if it is real, how about adding a small circulating pump in the tank to keep it stirred up? Seems a lot simpler to me!

Jim

Regarding separation, no I have no proof of that, but as Oil and Petrol have different densities I do see a risk of that happening when at anchor for some weeks.
Especially as it's a rather tall reservoir (stainless steel drum repurposed).



If you pour some oil and petrol into a tall glass and let it sit, it's very likely to separate. Gently rocking it would not remix it. Guess heavy weather would do the trick, but we try to avoid that.

Now your idea is a clever solution. Simple and easy to implement. Thanks, I like it!


Regarding Benz's comment about water in fuel, we always use a water separating funnel when refueling and have a water removal centrifugal filter in the fuel pick up hose. So I hope that helps, besides usually using shoreside filling stations rather than marine ones. Usually they are cheaper and have cleaner petrol because they sell a lot more of it in a given time span.

It was also suggested a bit of alcohol into the tank to get rid of any water.