LPG & Water in petrol tank.

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LPG & Water in petrol tank.

#1 Post by xjman » Fri Jul 31, 2009 10:38 am

Hi fellow LPG'ers,
I have a 1993 Jeep XJ with a single point LPG system, I have owned this for about 5 years, I have sorted out all LPG related problems in that time and it runs like a Rolls Royce on petrol or gas. The problem is I am now on my 3 rd. in-tank petrol pump!!! The last one (An Airtek, bought from the USA) only lasted 11 months, on taking it out it was covered in rust. This started me thinking and I eventually realized (being a bit slow) that water in the petrol was causing the problem. Next question is why is there water in the petrol? Some time back all UK petrol had to have so much Ethanol added to it, Ethanol attracts water, so here was a clue. I can if I tried make a tank of petrol last 12 months by running mostly on LPG, here was another clue, stale petrol. Boat users in the USA are having corrosion problems due to Ethanol and the fact that like me their petrol has been hanging around, sometime for months. This corrosion problem would not affect someone running only on petrol as they would have fresher petrol in the tank with very little if any water in it. I am looking for something I can add to the petrol to prevent corrosion, top of the list so far is Sta-Bil from the USA which is supposed to prevent corrosion etc. Any other suggestions, comments, welcome.

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#2 Post by Active_Lad » Fri Jul 31, 2009 2:18 pm

Ethanol is known to be an oxidant when in the presence of oxygen, so it is likely that you will have created a problem by running a tank of petrol for a long time i.e. the pump will have spent a long time "in the air" when the tank is low. Petrol also lubricates the pump, so if it keeps on running when it's not pulling fuel, this can lead to premature failure. Tanks with little petrol in them can also cause moisture to develop, further accelerating the oxidation process. Although we don't like paying for the stuff, I think you'd be better off keeping more petrol in your tank.
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#3 Post by rossko » Fri Jul 31, 2009 4:03 pm

There may be another side effect of long periods with low petrol. As the pump still circulates fuel, the tank will get warmed up every trip and heat cycle. That should cause a pumping effect as the vapour expands, later cools and sucks fresh air back in. Keeping the tank full(er) should minimise the effect.

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#4 Post by junkcatcher » Fri Jul 31, 2009 7:17 pm

In addition to running with more petrol in the tank for the reasons Rossko gave I would check your filler cap and breather system ---- if there is enough air and moisture in the tank to cause rust then you have potentially a high enough % oxygen content in the tank to cause an explosion.

Normally in a petrol tank the fuel vapour displaced so much air the the space above the fuel in the tank has a very low oxygen content which both prevents an explosion and virtually stops any rusting on the inside.


#5 Post by GazNicki » Fri Jul 31, 2009 9:45 pm

Thanks to Tesco's 5p off per litre not covering LPG and the LPG system working 100% now, I am personally hoping to be running with a full tank of petrol for the most parts. This should also help to get a more accurate reading on my MPG and fuel consumption if each time I fill with LPG i can simply top up with a little petrol too.

I would suggest running with more petrol in the tank. I was advised from the start to keep the petrol tank with a healthy amount of fuel in it, for more than just emergencies.

1/4 tank should be OK, but on my Mondeo 1/4 tank doesn't seem to last very long so £20 usually goes in the tank on an LPG fill-up. I find I can go through this in a week and a half if the runs are not very long.

Brimming the tank should remove any excess oxygen from the tank and reduce the chance of rusting. An expensive prevention, but can be managed quite comfortably after the initial outlay by topping up frequently.

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#6 Post by SimonHobson » Sat Aug 01, 2009 2:24 pm

I've had similar problems. As part of my conversion, I fitted a replacement petrol tank that goes under the rear wheel arch and frees up the space originally taken by the 20g tank for a gas tank. Trouble is, being mild steel and having absolutely zero internal treatment, it's rusted as well.

The rust & water forms a brown sludge that blocks the suction strainer sock on the pump, the pump then get noisy, and if you leave it long enough it fails. For now I've just cleaned the sock and fitted a spring in it so it can't collapse, but I've had POR15 recommended to me - and I intend treating the inside of the tank with that when I get around to it.
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#7 Post by xjman » Sun Aug 02, 2009 11:15 am

Thanks for all the advice/tips etc. I think my problem is a combination of a 15 year old rusty petrol tank, the adding of Ethanol to petrol, and running mostly on LPG so the petrol is staying in the tank longer. There would probably not have been any problems at all when there was lead in the petrol! Time to start thinking about solutions if any.

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#8 Post by jalfrezigazee » Tue Aug 04, 2009 11:25 am

one last thing to check. Look at the small breather hoses on the fuel filler system. If any of these have split then the rear wheels will cover it with water when driving in the rain and this easily gets into the tank. Used to be a big problem on the first fwd Vauxhall cars

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