Water/Condensation in petrol problem

[galeus]

On our boat we have a back up, 10hp o/b engine which requires a separate fuel tank big enough to be useful on a coastal stint.
For the third year running I'm now having the carb. stripped, tank and fuel line cleaned out because of condensation in the tank.
I have also asked the mechanic to fit a water separator which he will rig up temporarily with cable ties beneath my davit; but this will not stop the problem.
The 25 litre tank sits on the back deck (I don't want it inside the boat) and I fill it to about 20 litres in June/July when we set off for our boat trip. I don't fill it to the top because I worry about expansion causing a problem.
This can't be a new problem, so I'm hoping somebody has experienced similarly and I can reap the benefit of their advice.
Cheers Richard

 

[AngusMcDoon]

Never had condensation in a petrol tank. Are you sure it's not getting in through the breather as it's outside?

 

[VicS]

On our boat we have a back up, 10hp o/b engine which requires a separate fuel tank big enough to be useful on a coastal stint.
For the third year running I'm now having the carb. stripped, tank and fuel line cleaned out because of condensation in the tank.
I have also asked the mechanic to fit a water separator which he will rig up temporarily with cable ties beneath my davit; but this will not stop the problem.
The 25 litre tank sits on the back deck (I don't want it inside the boat) and I fill it to about 20 litres in June/July when we set off for our boat trip. I don't fill it to the top because I worry about expansion causing a problem.
This can't be a new problem, so I'm hoping somebody has experienced similarly and I can reap the benefit of their advice.
Cheers Richard

I have a similar sized outboard tank.
In nearly 30 years I have not suffered from any condensation nor have I had to strip and clean the carb.

Perhaps the filler cap on your tank is not making a tight seal or perhaps the vent is not closing tightly.

I must admit that my tank is not left out on deck 24/7. It's stowed in the cockpit locker when the boat is not in use.

When appropriate I protect cap and vent with a plastic bag or even cover the entire tank because otherwise I am sure the design is such that rain or spray would find its way into the tank via the vent.

I always empty the tank at the end of the season and any fuel I keep is stored in full, tightly capped metal cans and filtered before use the following year.

I think you will find that it is common, if not normal, practice to fit a filter and/or water separator to fixed installations but I guess these have a permanently open vent unlike portable tanks which have vents which can be closed.

 

[AngusMcDoon]

This is an interesting article...

http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm

Basically, he says condensation in fuel tanks is a myth. The atmosphere does not have the capability to hold enough water as vapour and fuel tanks don't change temperature sufficiently for it to condense out anyway. Given his figures the amount of water that could condense out of the small volume of air in an outboard engine's fuel tank is absolutely tiny.

 

[galeus]

Thanks for your advice which is interesting.
I cannot say I am certain that the problem is condensation, but we do fit an inverted 'tupperware' tub and lid with a hole cut in the lid which is larger than the neck of the tank but smaller than the screw top, which allows air in but not rain or spray. Interestingly this transparent tub nearly always has condensation in it that you can just about pour out.
I've left the tank, fuel line and carburettor with Walton on Thames 'Ting Dene' engineers on site so I can't say anymore about the integrity of the tank, fuel connection apart from when I filled the tank in June at the filling station and carried it to the boat, no fuel leaked out.
Thanks again Richard

 

[gordmac]

I think you can get fuel additives for this.

 

[Bandit]

Lets call it water in the fuel.

Assuming your tank is one of those red plastic ones, you would be able to tilt the tank so that in strong daylight you can see the water in a bottom corner when looking through the filler hole.

I made up a suction device with an outboard squeeze pressure bulb (those black squeeze things between a remote tank and an outboard) a length of fuel hose and a couple of feet of copper tube.

Look in the tank when you tilt it, see the water , put the copper tube in it, You then suck up the water, including some petrol, pump it into a bottle, let it settle and decant the petrol back into the tank and discard the last. Bit with the water in it.

Job done.

 

[vyv_cox]

I am currently experiencing a similar mystery. I have a 2.5 HP Mercury 2-stroke that had only run 6 hours when I bought it. Ran perfectly on the only occasion it was used, September last year. The carburettor was run dry, it was left on the transom until about November, then stowed in a locker until last week. Refused to start but would run on Easi-start, spark clearly OK, so I suspected fuel. Topped up the part full tank of last year's fuel with fresh bought at Tesco (huge turnover so unlikely to be defective). Still wouldn't start. Dumped the contents of tank and refilled with the fresh stuff. Still wouldn't start. Brought the engine home, stripped the carburettor, no obvious problem. Took off fuel hose to check no blockage, contents looked surprisingly like water. Drained the tank into a jar, found:

Baffling, I have no idea how water could have got into two separate lots of fuel.

 

[chewi]

On our boat we have a back up, 10hp o/b engine which requires a separate fuel tank big enough to be useful on a coastal stint.
For the third year running I'm now having the carb. stripped, tank and fuel line cleaned out because of condensation in the tank.
I have also asked the mechanic to fit a water separator which he will rig up temporarily with cable ties beneath my davit; but this will not stop the problem.
The 25 litre tank sits on the back deck (I don't want it inside the boat) and I fill it to about 20 litres in June/July when we set off for our boat trip. I don't fill it to the top because I worry about expansion causing a problem.
This can't be a new problem, so I'm hoping somebody has experienced similarly and I can reap the benefit of their advice.
Cheers Richard

I have been having these issues with my Honda BF2. outboard, and I think it is the storage of the fuel that is an issue. I keep mine in the tender in 5 litre plastic cans, I think the cans condense overnight, shrink,eventually suck in fresh air with new moisture content, and repeat the cycle. I have taken to storing the cans in a box out of sunlight, and I think it has improved, but its early days.
You can also help yourself by using a funnel that traps the water, a small amount of water does not get over a lip to get into the tank, pour the residue back to the tank. Check the last inch or so of fuel before you use that.

 

[lw395]

I have had problems with condensation occurring in carbs.
Mostly on my outboard, which lived in a damp shed at the sailing club. I became adept at draining the carb into a polythene milk bottle and pouring the good fuel back in.
Also when I had a Moto Guzzi. I believe evaporation of petrol from the carb caused cooling condensation, some of which would end up in the float bowl. This bike had open bellmouths so carbs very open to the air when not running.
A small filter will trap any water coming from the tank, every outboard should have one.
But carbs in a damp environment are vulnerable.
Also there is a theory that fuel cans which are wet can suck water in as they cool down if the cap is not 100% tight. I mean liquid water lying on the tank top.

 

[duncanmack]

I am currently experiencing a similar mystery. I have a 2.5 HP Mercury 2-stroke that had only run 6 hours when I bought it. Ran perfectly on the only occasion it was used, September last year. The carburettor was run dry, it was left on the transom until about November, then stowed in a locker until last week. Refused to start but would run on Easi-start, spark clearly OK, so I suspected fuel. Topped up the part full tank of last year's fuel with fresh bought at Tesco (huge turnover so unlikely to be defective). Still wouldn't start. Dumped the contents of tank and refilled with the fresh stuff. Still wouldn't start. Brought the engine home, stripped the carburettor, no obvious problem. Took off fuel hose to check no blockage, contents looked surprisingly like water. Drained the tank into a jar, found:

Baffling, I have no idea how water could have got into two separate lots of fuel.

Viv, what percentage of the fuel that was in the tank does that water represent? Might it be @5%?

Reason being, now that we have Bioethanol Petrol it is more likely than not to "phase separate" if there is more than 40ppm (yes, parts per million) water in it.
Test for what it is using "Kolor Cut Water Finding paste - Modified for Reformulated and Oxygenated fuels" (the original only tested for water). It tests for water or bioethanol. You may be able to blag some from your local friendly petrol station.
It may be bioethanol in which case the fuel has separated. We're seeing it in vehicle tanks, but we have knowledge of garage tanks doing it. It's going to get worse as the level of Bioethanol in the petrol increases (currently up to 5% and proposed increasing to up to 10%)

 

[VicS]

Viv, what percentage of the fuel that was in the tank does that water represent? Might it be @5%?

Reason being, now that we have Bioethanol Petrol it is more likely than not to "phase separate" if there is more than 40ppm (yes, parts per million) water in it.
Test for what it is using "Kolor Cut Water Finding paste - Modified for Reformulated and Oxygenated fuels" (the original only tested for water). It tests for water or bioethanol. You may be able to blag some from your local friendly petrol station.
It may be bioethanol in which case the fuel has separated. We're seeing it in vehicle tanks, but we have knowledge of garage tanks doing it. It's going to get worse as the level of Bioethanol in the petrol increases (currently up to 5% and proposed increasing to up to 10%)

I thought the trouble with ethanol in gasoline was that the ethanol is hygroscopic and so tends to attract water.

 

[duncanmack]

I thought the trouble with ethanol in gasoline was that the ethanol is hygroscopic and so tends to attract water.

Yes, true. But when/if the ethanol has more than 40ppm of water more than the formulation then the ethanol is no longer soluble in gasoline - it phase separates into petol on top and diluted ethanol on the bottom. If the sample is new/clean and from clean tankage then the ethanol is fairly clear or with a tinge of yellow. You could think it was just water.
I had a hell of a problem with one of my garage petrol tanks about 2 years ago and had to do a load of research on the subject to prove that the water contamination did not come from my installation. The research threw up some interesting but depressing facts about Bio-petrol.
Sorry, I should explain that before Bio it was possible for some water to be in suspension in the petrol and caused little problem. Ethanol, however, removes this but can cause a problem in itself.

 

[galeus]

Thanks Bandit,
Yes it is a red plastic one, your advice is certainly useful but you sound like you also expect to find water in your petrol: where do you think your water is coming from?

 

[VicS]

Yes, true. But when/if the ethanol has more than 40ppm of water more than the formulation then the ethanol is no longer soluble in gasoline - it phase separates into petol on top and diluted ethanol on the bottom. If the sample is new/clean and from clean tankage then the ethanol is fairly clear or with a tinge of yellow. You could think it was just water.
I had a hell of a problem with one of my garage petrol tanks about 2 years ago and had to do a load of research on the subject to prove that the water contamination did not come from my installation. The research threw up some interesting but depressing facts about Bio-petrol.
Sorry, I should explain that before Bio it was possible for some water to be in suspension in the petrol and caused little problem. Ethanol, however, removes this but can cause a problem in itself.

Thanks. It would be interesting to find the phase diagram. although I think Id struggle with a 3 component one now.

EDIT It was not difficutl to find it ... now try to understand it!

 

[vyv_cox]

Vyv, what percentage of the fuel that was in the tank does that water represent? Might it be @5%?

Difficult to judge as I dumped the mixture of old and new fuel and then topped up with new. Assuming the water was all in the bottle, at a guess it might be up to 10%. I will not be able to examine the fuel bottle until next week, will then know if there is more water in it.

 

[chewi]

Viv, what percentage of the fuel that was in the tank does that water represent? Might it be @5%?

Reason being, now that we have Bioethanol Petrol it is more likely than not to "phase separate" if there is more than 40ppm (yes, parts per million) water in it.
Test for what it is using "Kolor Cut Water Finding paste - Modified for Reformulated and Oxygenated fuels" (the original only tested for water). It tests for water or bioethanol. You may be able to blag some from your local friendly petrol station.
It may be bioethanol in which case the fuel has separated. We're seeing it in vehicle tanks, but we have knowledge of garage tanks doing it. It's going to get worse as the level of Bioethanol in the petrol increases (currently up to 5% and proposed increasing to up to 10%)

Thanks duncanmack,
Do I understand this right...
"Good" petrol now contains bioethanol is stable provided it doesnt get 40ppm of water, but once it exceeds that both the water and bioethanol settle?

 

[duncanmack]

Thanks duncanmack,
Do I understand this right...
"Good" petrol now contains bioethanol is stable provided it doesnt get 40ppm of water, but once it exceeds that both the water and bioethanol settle?

The bioethanol, with the water in solution, settles from the petrol - 2 layers.

 

[chewi]

The bioethanol, with the water in solution, settles from the petrol - 2 layers.

Thanks a bunch, I couldn't understand how so much water got there, but if its bioethanol split from the water by the condensation the amount makes more sense.

Next question if I may... what can be done to keep the original petrol more stable?
additives? premium petrol? shade? metal cans?... I don't really want to keep the cans in the car, so the tender is best for me.

 

[chewi]

Thanks a bunch, I couldn't understand how so much water got there, but if its bioethanol split from the water by the condensation the amount makes more sense.

Next question if I may... what can be done to keep the original petrol more stable?
additives? premium petrol? shade? metal cans?... I don't really want to keep the cans in the car, so the tender is best for me.

Answering my own question... I have written to Tesco, Texaco, BP and Shell , and only BP have replied to say that there is an ethanol free Petrol in BPUltimate.
The others have either not disclosed, or didclosed with caveats to say there might be ethanol there, even in their premium fuels. An old post on a triumph owners site I found says Texaco premium is ethanol free, but it is no longer


(btw Shell said there was up to 7% in their diesel, but I didn't ask about that so can't compare other brands)


BP ultimate more expensive than common petrol, but if avoids phase separation and keeps corrosive ethanol out of my fuel supply its good for me.

as an aside of course with Wniter approaching, it would be folly to leave the ethaonol in the engine for the winter.