MD7A New Fuel Tank ... top or bottom feed?

[gandy]

Hi,

We're replacing the fuel tank on our Griffon, and I need to get it ordered pretty soon. I've done all the measuring and worked the correct fittings and their appropriate places.

I just need to decide whether to stick with the existing feed arrangement with the fuel tap at the bottom of the tank, or to go with the so-called modern practice of drawing from the top via a dip tube. As far as I can see the disadvantage of the top feed is that any sort of small leak is likely to go unnoticed as air will be sucked in rather than fuel leak out, and of course that will stop the engine. Also there's an extra complication in the fitting of the dip tube, and again any imperfection or fault there will bring things to a halt.

Conversely using the original method the fuel supply to the engine is more secure, but with the risk that a fuel leak from pipework etc could empty the whole tank. I'm inclined to favour sticking with this arrangement.

One possible issue may be that the tap can't be fitted as near to the bottom of the tank as I would have liked, maybe leaving a greater unusable volume than I would have with a dip tube feed. I intend to mitigate this a little by sloping the tank by around 10mm. Its unfortunate that access to the space means I need to fit a fairly flat tank.

Any comments or thoughts? In particular I would be interested in experience from anyone with a similar age or type of engine. The comments from other owners all seem to be from people who've replaced the engine as well.

Thanks, Tony S

 

[ghostlymoron]

I would go for a top feed but make provision for a bottom drain and small sump for collection and removal of crud. Also maybe add another takeoff for Eberspacher so that you can fit in the future. In these days of dirty fuel/ diesel bug, it's a good idea to have an accessible hatch in the top for cleaning.
Finally make sure that the new tank be fitted through the existing hatch.

 

[gandy]

Cheers. I'm not going to fit a drain, I can't see me ever wanting to take a plug out of the bottom of a full tank.

Personally I would prefer not to have any space for crud to collect, I'd rather it was drawn out in normal service and caught by the (large) primary filter. Its different with a static tank, but on a boat the trouble with having a sump is that all the ****e collects there, and then an unlucky lurch at the wrong time could deliver it all at once.

I should have explained that this is a sailing boat, normally using only 10-20 litres a year and I intend to fuel with clean white whenever possible.

Access for fitting is an issue! There's room for a much taller tank, but I wouldnt be able to get it in place.

 

[macd]

I'm not going to fit a drain, I can't see me ever wanting to take a plug out of the bottom of a full tank.

'Best practice' (according to Calder, anyway) is for a top-exit drain, much like a top exit outlet, but piped right to the bottom of the tank. I have one and once primed six years ago, it's stayed primed since. A hose from it leads to a tap in an accessible position in the engine bay: it takes me literally two minutes to check for/drain any crud.

Tek-Tank can supply a cover for fitting to any tank, whch includes outlet, return and breather take-offs, also acting as a (rather small) inspection cover. It has no provision for a drain, though.

 

[NormanS]

I would always have a sump with a drain valve, and check it regularly. That way, it is working for you all the time. Every time the boat moves, and crud is gently encouraged to fall down into the sump out of harm's way.

Personally, I prefer a bottom, or more accurately, nearly bottom, outlet. It seems much more natural, and usually makes bleeding the system much easier.

 

[gandy]

That "top drain" sounds clever, but if it's permanently led down to a low level tap, then I can't see there's much benefit compared to a drain tap on the tank. A leak or failure at that low level drain tap is going siphon out the entire tank contents.

 

[VicS]

Hi,

We're replacing the fuel tank on our Griffon, and I need to get it ordered pretty soon. I've done all the measuring and worked the correct fittings and their appropriate places.

I just need to decide whether to stick with the existing feed arrangement with the fuel tap at the bottom of the tank, or to go with the so-called modern practice of drawing from the top via a dip tube.

Thanks, Tony S

Your choice entirely I would say whether you go for a top or bottom take off. Why not replace like with like?

I would try to incorporate a small sump with a drain valve if possible though. It can only be a good idea. ( plug the valve to prevent accidents)

 

[capetown]

Had a new tank made in ss for my Pageant about 8 years ago.

With the Volvo MB7A engine out of the boat, I measured up then made a cardboard mock up just to be sure, it also had to be shallow.

Went for the near base outlet/feed option, like for like.

My stainless tank was pressure tested, there's probably a spec on it, but they tested mine with mains water pressure, wish I knew about adding dye to it then, would have saved some problems.