Best way to fully empty built in diesel tank?

[MalcolmP]

With all the concerns about diesel bug / growth sludge especially when using diesel with increasing amounts of bio-diesel, I am planning to leave our fuel tank empty this winter (normally I have kept it full with bug inhibitor).

So would like your educated thoughts on best way to extract it when we lay-up. Wondering if I remove the fuel gauge sender, I can put in a hose and use a pump such as:

www.homebase.co.uk/stanley-pump-13mm-pump-sta40200-xj/12810869.html



Connected via suitable hoses to jerry cans. Fortunately I will be able to empty the jerry cans into my MoHo tank.

I also thought about using the fuel return line back to the tank from the injectors, but this would mean running the engine, and perhaps could be messy...

Welcome other ideas

Thanks

Malcolm

[Mistroma]

I moved away from leaving the tank full a couple of years before Covid. I usually run the tank down to about 30 litres and double dose with Marine16. I syphon out from the bottom of the tank pre-launch and end of season after letting it settle for a week or so.

Pre-2012: Red diesel and then white diesel in France, negligible residue in sump.
2013-2015: Small black residue (approx. teaspoon, increasing each year to about 30mls)
2016- onwards: Steadily increasing black residue. Approx. 500mls cloudy fuel increasing to 1-2 litres.

The residue probably doesn't contain much diesel bug. I think most is ashpaltines due to recycling hot fuel from the engine and storing it in the tank at 25-40C during the summer.

I think it is now a good move to keep the tank pretty empty over winter but don't see the need yet to completely empty it. However, that might change as I'll be looking into my tank in the next few days. I left the boat in October 2019 and have only just returned. It will be interesting to see what's in the tank.


1) Access to tank to empty
I remove the level sensor twice every year, no problems with leaks so far. I clean the faces with acetone and seal with a neutral cure sealant. I smear a little on the rubber gasket, taking care not to leave enough to squeeze some into the tank. I tighten the screws carefully without a lot of force and build a thick layer of neutral cure sealant in the depression around the sensor.

2) Pump
I don't know if that pump will handle diesel, probably best to ask the manufacturers. I have seen diaphragms and impellors go soft an swell up after a short time. They were designed for water, not diesel.

3) Alternative options if you can't find a suitable pump
Either: Run tank down to 30 litres and double dose with biocide. It works for 6 months and I'll let you know if it is still OK after almost 2 years.

Or: Syphon the fuel when ashore, easy enough with a long hose, valve and priming device. It's a doddle for water tanks as you just connect to a hose, back flush to tank, disconnect and let it run. Slightly tricker for diesel and it helps to have 2 people as the hose will not want to remain at the bottom of the tank (unless you attach a rigid pipe).

[Charlie-Bravo]

Suppose it depends on how much fuel is in the tank, but a drill powered pump might take a while , and  how much fuel will remain in the tank once pumped out? 
Will you open the top of the tank ( if it has a hatch ) to give it a clean out? .... not that you can reach the corners easily.

Short of an internal tank polish, which I have only done once, and not on this boat, not a nice job,  how do you feel leaving it more or less empty is better than leaving it full? bug will grow in a jam jar full left in the bottom joining with the condensation water, awaiting your filling next season, sludge is partly what filters are for, and if they can't cope a tank washout is due.

I intend keeping mine full and treated, partly as I like to keep the availability of using the boat throughout the winter, and if and when I get the sludge and bug ( probably when not if) I guess pulling the tank out and sloshing it out with petrol, washing with soap, blow drying then re installing it will be the job, at least my tank looks removable, but interested in your intentions, what happened to promote the new tack on this line of maintenance?

will watch the thread with interest, perhaps I'm missing something.

CB

[NZL50505]

Yes I’m also curious why the switch from keeping it full and treated - has that not worked recently?

Given bug loves the interface between water and diesel the goal is obviously to minimise either the water or diesel or both. Plus using treatment just in case. I can see how a brim-full tank virtually eliminates opportunity for condensation to form in the remaining air pocket. But as you say it’s hard to totally empty a tank of diesel in-situ so I see potential for much more condensation leading to water / diesel mixing in even higher water ratios using this approach?

And once the season starts, before you refill with diesel, you’ll want to draw through whatever has accumulated in the tank over winter to remove the condensation (water) at the very least. And then resume the normal regime of managing a partially full tank throughout the season using treatment?

It’s a bit like learning to live with bug rather than relying on an elimination strategy!

[MalcolmP]

Many thanks for those thoughtful replies. That pump I put the link to is not rated for fuel, so have not bought. Agree the method I have used to date has been fine. I am getting the existing contents professionally filtered and polished with a double Racor system next week. Will see what sludge that shows up, but now thinking I will continue to treat with Biocide and keep tank full next winter.

[NZL50505]

I think your approach & setup sounds pretty robust and includes all reasonable steps to minimise the risk. I would continue with that!

[rxc]

Malcolm,

I used this pump, from Amazon, and it works quite well. The pump is rated for water and fuel (both petrol and diesel) and the leads are long enough to reach 12v on the engine. I mounted it on a stick because the hose I attached had a curve that was made it difficult to move around.

www.amazon.com/gp/product/B07GWXCZTB/ref=ppx_yo_dt_b_asin_title_o09_s00?ie=UTF8&psc=1



I don't know how you plan to get into the tank - I had to make up a special fitting with 5 "fingers" and a triple-nutted bolt to turn the access plug in my tank. It worked quite well once I re-engineered it a few times to incorporate a piece of metal to handle the shear loads - wood is not strong enough.






With the access plug removed, it was possible, but a stretch, to reach the entire tank.

[MalcolmP]

Thanks RXC, that looks a useful little pump. There are no inspection hatches at all on the 39i. The guys who are going to clean and polish the existing fuel will remove the tank sensor. Depending on how much sludge they find, but I am now planning to go back to keeping the tank full next winter with Biocide.

[jy51]

Sept 11, 2021 11:16:37 GMT MalcolmP said:

With all the concerns about diesel bug / growth sludge especially when using diesel with increasing amounts of bio-diesel, I am planning to leave our fuel tank empty this winter (normally I have kept it full with bug inhibitor).

So would like your educated thoughts on best way to extract it when we lay-up. Wondering if I remove the fuel gauge sender, I can put in a hose and use a pump such as:

www.homebase.co.uk/stanley-pump-13mm-pump-sta40200-xj/12810869.html



Connected via suitable hoses to jerry cans. Fortunately I will be able to empty the jerry cans into my MoHo tank.

I also thought about using the fuel return line back to the tank from the injectors, but this would mean running the engine, and perhaps could be messy...

Welcome other ideas

Thanks

Malcolm

Malcolm, not sure why you think leaving the tanks empty is a solution, surely, it is impossible to completely empty a tank, leaving sludge and ideal conditions for condensation and diesel bug.  I have always left my tanks full to the brime over the winter months and never used a bug inhibitor and (touch wood)  have never experienced problems.  However, I would like to say I’m become a little paranoid and for the first time purchased a bug treatment, unfortunately due to a desire to leave the U.K. before lockdown, left before the delivery arrived, never mind maybe next year or as the Spanish say manana. 

[Mistroma]

Update after checking my tank.

I commented earlier that build up of black material had gone from zero to approx. 1 litre cloudy fuel and 100mls black residue. This has happened since about 2012 as I've sailed from Scotland to Greece.

I am careful to filter all fuel, treat with Marine16 twice and also check the tank twice a year as mentioned already. The residue I get has never really looked very much like diesel bug. I think it is Ashphaltines or other degradation products. The tank certainly gets very hot with re-circulated fuel on a long run.

I have just checked the tank after leaving the boat since mid. October 2019. I found traces of black oily residue (less than 1ml) and a litre or two of very slightly cloudy fuel (no visible particulates, just not clear). The residue removed in 2019 had settled to a black oily material with completely clear fuel above. No traces of diesel bug in either the tank or the residue removed in 2019.

I'm certain that the 30 litres in the tank has not picked up any significant water. It makes sense that long term cooler storage has had less of an adverse effect than my usual long runs in 30-40C weather. Leaving the tank fairly empty does appear to work for me. I don't feel the need to completely empty the tank.

I am always careful to grease the filler cap o-ring and see excess grease when tightening. I think that much of the moisture "breathed in" may well be leakage via a poorly sealed filler cap in some cases.

Others may suffer from diesel bug in cold, wet climates. Greece is very dry in summer but certainly pours down in winter.

[NZL50505]

Sept 13, 2021 20:46:26 GMT Mistroma said:

I think that much of the moisture "breathed in" may well be leakage via a poorly sealed filler cap in some cases.

Don’t forget the breather pipe.

[rxc]

Sept 13, 2021 6:15:28 GMT MalcolmP said:

Thanks RXC, that looks a useful little pump. There are no inspection hatches at all on the 39i. The guys who are going to clean and polish the existing fuel will remove the tank sensor. Depending on how much sludge they find, but I am now planning to go back to keeping the tank full next winter with Biocide.

Malcolm,

The lack of an access hatch is really too bad. Good luck with your efforts. FYI, when I opened up my tank, to change the fill pipe gasket, the tank looked absolutely clean, other than the tiny cap gasket for the biocide bottle that dropped down the fill pipe when I opened it to add biocide. And my boat sits in humid S Florida all year round.

[Mistroma]

Sept 13, 2021 21:23:11 GMT NZL50505 said:

Sept 13, 2021 20:46:26 GMT Mistroma said:

I think that much of the moisture "breathed in" may well be leakage via a poorly sealed filler cap in some cases.

Don’t forget the breather pipe.

Most breather pipes are not mounted on deck in a position where rain water flows over the fitting. Fillers are often in line for a stream of rain water and can let in quite a lot of water if poorly sealed. Some people never inspect the o-ring or apply grease. I thought that was worth mentioning as a major risk. Breathers normally only allow moist air to enter, not drips of water.

I did see a boat in Spain with several containers full of water and diesel. They had purchased the boat recently and discovered that the breather was a mushroom vent on deck near the scuppers. A really badly designed installation on a steel hulled one-off. I think the vent was underwater on their first trip across Biscay.

I did read something a few years ago to indicate that the amount of water entering from a vent pipe would be miniscule. I keep meaning to do a calculation and discover if that is correct. I'd use my own empty tank, an average humidity in winter, extreme max. & min. likely for nnn days. It would give an indication but of course doesn't account for multiple temperature changes each day. I never seem to get around to it.

[MalcolmP]

Just to update this thread. The local professionals did a brilliant job with the clean. They removed the tank sender and extracted all the old diesel, there was only a very small amount of sludge in the filter and they said the tank bottom and sides did not have any growth. So they refiltered the diesel on the way back in. Very reassuring. I will keep the same regime for next winter, so fill the tank, plug the vent and add Biocide. Thanks for a your replies.

[rene460]

Hi Malcolm, just one small point on your procedure.  I am not sure where the “ plug the vent” step came from.  I would expect the vent to be required for breathing to accomodate the atmospheric pressure and temperature changes through the winter.

Probably only around 10 kPa, but not sure if the tank flexing can accomodate that.  

I usually add a small dose of biocide after most tank refills by pouring it through the fill pipe.

Glad the fuel cleaned up ok.

rene460

[johannes]

If the tank is full I suspect the air exchange via the vent will be negligible.

I store the boat with the tank filled over winter, and I always use pure dino diesel with no bio-diesel mixed in (our marina sells it at a premium).

[neworca1]

This is a little off topic, but for passage planning purposes I'm curious to know how much fuel remains in the relatively shallow, flat 238L diesel tank when the pickup tube starts sucking air. That is, what is the actual useful capacity (assuming the vessel is on an even keel)? Perhaps some of the contributors to this thread who have completely emptied their tank via the working pickup could tell me. Alternatively, does someone here know how far the pickup tube is above the tank bottom?