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Water in fuel

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RMA24/09/2019 12:37:02
217 forum posts
4 photos

Good afternoon. Are there any professional chemists on this forum?

I'm not a chemist but I fear this thread may develop into a long winded set of opinions and ideas, when I'm really searching for a quick definitive answer.

We have a current thread going on my car club forum regarding the damage caused to fuel tanks, pumps and fuel lines due to the ethanol content in modern fuel. This apparently encourages water which settles at the bottom of the tank and consequently rusts these components.

I would really appreciate an answer from a chemist who might have a method of dispelling the water or stop it happening in the first place. We know of several additives on the market, but are these any good or just another way of throwing money away?

Thanks in advance

Robert Atkinson 224/09/2019 13:00:34
463 forum posts
21 photos


Sorry not a chemist but do know something about alcohol in aircraft fuels.
Ethanol in petrol does not attract water, but would rather dissolve in water than fuel so if you add say 2ml of water to a 50ml sample of fuel containing 2% ethanol, shake it and lit it settle there will be 4ml of "water" at the bottom of the container. This is of course 2ml of water and 2ml of ethanol. The ethanol does not attract extra water to the fuel. The test above is an approved method for determining ethanol content in motor gasoline "Mogas" (petrol) before using it in aircraft that are approved for it subject to ethanol limits. Amongst other things ethanol can cause some plastic or GRP fuel tanks to fail.

To get water out of your fuel, add isopropyl alcohol (IPA) This should ideally be 99% pure but 70% or higher is OK. It absorbs water and is miscible with petrol so keeps the water in suspension and allows it to be carried into the engine and discharged through the exhaust at a constant rate that does not affect combustion. Most commercial fuel "dryers" are just IPA.

Robert G8RPI.

RMA24/09/2019 13:31:53
217 forum posts
4 photos

Thanks for your response Robert. Yes, we check for water in the aircraft tanks with Avgas, easy to do on a 172, but not so easy on a car. Like the aircraft I always leave my car with a full tank to minimise condensation, and I run it regularly even if only in the garage, but without stripping it down, it's impossible to know if there is water/corrosion in my tank.

This problem was highlighted recently when a member started to investigate his 'fuel' problems and lack of power (normally around 310 BHP) . He'd already recently changed the fuel pumps and filters, but when he stripped it again and put the photos on the forum, the amount of corrosion was alarming. He has now changed the tank, plus the pumps and filters again. His investigations found that ethanol attracted water. Apparently the government will be increasing the mandatory limit of ethanol and many engines will not be able to use it if it goes too high. Maybe you can enlighten me on that.

I know it's a good idea to put an additive in the tank if it's to be left say, over the winter without any use, but once you start to use up the fuel and refill, the additive becomes weaker and loses it's benefit.

I'll look into the IPA (not the beer) and forward the information.

Thanks, Rodney

Clive Hartland24/09/2019 14:12:20
2493 forum posts
40 photos

One time I filled at a newly opened gas station, I use diesel, shortly I had engine problems and found that there was water in my fuel filter. I ended up buying a new fuel filter untit complete due to corrosin of the body inside.

Complaint to the gas stations just drew blank stares. Ever after that I had to have one of those fuel line filters which collected all sorts of muck.

Obviously not of much use to teh poster but as a source of water maybe.

john fletcher 124/09/2019 16:50:52
564 forum posts

When I worked for BR in the 1960's, diesel arrived in large tankers by rail, it was off loaded into large storage tanks each mounted on a slight gradient. It was the duty of the fuel storage operator to open the bottom water tap of the tanks every day to drain away the water. It was surprising just how much settled water there was in the tanks. That of course was why the tanks were so mounted, water being more dense than fuel oil. John

Tim Stevens24/09/2019 16:59:26
1122 forum posts

Try to remember that old cars always include a small amount of water in their fuel tanks. Condensation, mainly, and the only cure is to live in Wagadugu. The problem is, I guess, not really to do with the water that's in there and has been since Stanley Matthews was in short trousers, but to owners who read an article which includes 'faults', and who then are convinced that they have got a problem. No real symptoms. Another cause is owners of up to date fuel injection motors for work, who expect their MGA to warm up in exactly the same style.

Imagine the situation in the old days - no air filter, bike or car. Drive in heavy rain and you certainly have water mixed with your petrol as it goes into the engine. Did it cause problems? Very rarely.

Start your engine on a nice autumn morning with a light frost, and look at the body of the carb. It will be drenched in nice clean water - condensation again. If you were too eager, the engine might fluff and die. So, leave the engine at about 1500 rpm for a few minutes, and all should be well.

Happy motoring


not done it yet24/09/2019 17:21:03
3806 forum posts
15 photos

Just to add some extra, probably red herrings, to the discussion, do remember that ethanol is broken down by some microbes to acid. If that occurs in the fuel system, expect eventual corrosion - not a strong acid, but a lowered pH all the same.

Dave Halford24/09/2019 18:40:26
527 forum posts
4 photos

Plenty of car fuel tanks used to rust through in the seventies, likewise motorcycles and lawnmowers, then it was just lead as an additive (I'm ignoring Cleveland Discol ).

Leaving the cap off stopped lawnmower tank rust in the shed.

I thought the issue with modern fuels was gumming in the fuel lines when left standing?

Vic24/09/2019 19:03:25
2387 forum posts
12 photos

The Isopropyl Alcohol idea is interesting. I’m sure I read somewhere that a small amount added to petrol can improve the MPG of cars but never seen it confirmed.

RMA24/09/2019 19:11:23
217 forum posts
4 photos

My original question was whether there's a professional chemist on the forum. It seems there isn't, not so far anyway. Thanks for your comments. Should a chemist, industrial or otherwise have the answer to my question, please pm me, as these threads can go on and on.

Thank you

Daniel24/09/2019 19:22:30
255 forum posts
39 photos

Will water alone cause rust, in the absence of air (being covered by the fuel) ?

Maybe fit a drain cock to the tank, as per John Fletcher's anecdote. angel



Vic24/09/2019 20:23:28
2387 forum posts
12 photos

I thought Robert gave you the answer RMA. Just add some Isopropyl Alcohol? wink

fizzy24/09/2019 21:16:57
1657 forum posts
114 photos

Studdied biochem at uni long ago...but....IPA will keep the water in (the fuel) solution and thus minimise corrosive effects. It has bveen used in vehicles up to 40% bv but this can be counter productive to longevity. It is reccommended not to exceed 10% bv in a petrol car. At 10% the RON will roughly increase by 2.5 which is good news for your engine, so its a win win realy. I dont have first hand experience of commercial addatives but its most likely just dressed up IPA...why reinvent the solution?

Howard Lewis25/09/2019 12:12:46
2614 forum posts
2 photos

Water VAPOUR entering the engine will do little harm, may even do some good, (internal cooling effect ).

Old marine engines used to have water drips into the air intake for when working hard for long periods.

Water in fuel is bad news.

May well bring a carburetted engine to halt if ingested in sufficient quantity.

Putting aside any damage to pipe lines, filters etc, Bad news for fuel injected petrols, as will reduce lubrication of the feed pump and the injection system.

RUINOUS for Diesels. The clearances inside the injection pumps are lapped fits, so barely microns. At internal pump pressures of 500 bar, seizures took place, so no hope for the current common rail systems generating 1000 - 1500 bar. I have suffered pump seizures from water in fuel.

If in doubt, fit a water trap in the feed line, but do ensure that the connection are leak free, and drain regularly, ie frequently! Drain any water out of the fuel filter, if it has a drain facility.

The water probably comes from seawater being used as used as ballast in coastal tankers when returning empty to base, and then not completely pumped out. I once drained over 35 gallons (160 litres ) after receiving a delivery of 3,000 gallons (13.600 litres ) of DERV.

We used to check our fuel storage tanks for water, every week, and certainly after a delivery had settled.



Edited By Howard Lewis on 25/09/2019 12:13:57

Tim Stevens25/09/2019 13:05:55
1122 forum posts

Dave Halford suggests leaving the fuel cap off. This will perhaps tend to reduce problems of condensation (as the inside and outside temperatures stay much the same). But it will do no favours for cold starting. This relies on fairly light and easily evaporated molecules, and they are the ones that will evaporate into the air when the cap is left off*. This is the main reason that 'stale petrol' is used for washing off oily parts, rather than as a fuel. [But not, of course, in the working environment, where in any case the open tank should have been flagged up as a hazard]

*and this is a major factor making a choke necessary. To increase the amount of volatiles going in, we increase the amount of fuel going in. Modern sealed injection systems are quite different, the major reason being that they are sealed.

Cheers, Tim:

vintage engineer25/09/2019 14:02:30
215 forum posts
1 photos

I run a blown Lotus 7 and inject large doses of water and methanol when on full boost. This cause the incoming charge be cooler so produces more power.

Vic25/09/2019 14:19:41
2387 forum posts
12 photos

Many years ago I think the Post Office tried some kind of water injection system on their vehicles? I think they gave up after a while as there were no real benefits.

Dave Halford25/09/2019 14:26:14
527 forum posts
4 photos
Posted by Tim Stevens on 25/09/2019 13:05:55:

Dave Halford suggests leaving the fuel cap off. This will perhaps tend to reduce problems of condensation (as the inside and outside temperatures stay much the same).

I meant with the tank empty and it would also apply to Motorcycles laid up over winter. the tank stays dry.

Modern fuel systems use the water temp sensor mostly to work out the required fuel charge.

Tim Stevens25/09/2019 14:38:52
1122 forum posts

Water plus Alcohol injection was common for fighter planes as soon as extra max speed (however briefly) could save lives. Mainly the water does the charge- and cylinder- cooling and the alcohol stops it freezing before it is needed. And I suspect that the level of instruction, the degrees of skill, and the intense post-use checking led to Spitfires being more reliable than Morris Minor Vans.

Cheers, Tim

Edited By Tim Stevens on 25/09/2019 14:39:57

Michael Gilligan25/09/2019 16:46:26
14634 forum posts
634 photos
Posted by Howard Lewis on 25/09/2019 12:12:46:

Water VAPOUR entering the engine will do little harm, may even do some good, (internal cooling effect ).

Old marine engines used to have water drips into the air intake for when working hard for long periods.

[ ...]




The rain water blowin' all under my hood,
I knew that was doin' my motor good.



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