There is gasket material suitable for diesel fuel, but I doubt its cork. Permatex makes several products that are suitable for use with diesel.

 

Thats probably just a gasket sealer
Look for chemical resistance charts...easy to find

 

Scale is probably hard to perceive, but that looks like a man door. Wow. Very nice to have, although, I would prefer to have cutouts on the top.

Nevertheless, any auto parts store should have rolls of proper gasket material. Being on the side, I'd double it up with a gasket sealant too, which original installation thought of as well.

Clean tanks are probably the least attended to maintenance on all boats. Good for you to get it done. Get in a good discipline to use a bio-cide at every fill going forward. You need very, very little. Don't overdose. Also replace the o-ring on your fill cap. Second least attended to maintenance item.

 

I would think cork an appropriate material with Perma gasket #2 (non-hardening) as there are plenty of bolts to secure it flat.

 

cork mixed with Buna-N is used with diesel. a better gasket is made form Buna-N ( nitrile rubber ) closed cell foam sheet. it is available from Mc Master Carr for about $10 a running foot and comes about 50" wide, It has a lot of give easy to cut and the song has give to seal warped surfaces. McMaster-Carr is the one we use when hwen built SS tanks with access panels

 

we also us Permatex 85420 on the gasket

 

Would go to the McMasters site with your measurements. Would use gasket impervious to diesel not cork. Believe mine are nitrile and come for around $8 for ten so wouldn’t bother making them.

 

A thought...
That tank cut open on its side would scare me.
How is the cover secured

 

@Minnewaska yeah it's a pretty large opening, I managed to reach every corner of the tank inside. It's about 14"x10". I'm glad I cleaned it, I'm learning a lot doing this and there was quite a bit of slime in there. The slime looked innoffensive but when I cleaned it up, I realized some of it had grown some hard bits that would have clogged my fuel lines for sure. I'll definitely use biocide religiously going forward, along with the fuel polishing loop on a daily timer that I've been installing. I've also upgraded the primary filter with a Racor 500MA. Hopefuly they'll all work together to keep my tank clean and dry of water in the future.

@overbored and @outbound : I end up buying a sheet of Buta-N gasket material. Should I also use a sealant? I saw Permatex Aviation #3 being recommended, but also read that pure Buta-N doesn't need an extra sealant.

@RegisteredUser I agree it's strange. It was letting a bit of diesel seep. Hopefully the new gasket material will not have this effect. It's secured with a series of machine screws that are screwing in taped threads into the tank's aluminum.

 

Of course it may be fastened with self tapping screws,, What could go wrong? Even tapping for machine screws in 'thin?' plate wouldn't be my choice.

 

You answered my thoughts while I typed. AS for machine screws ,If tank wall is too thin for comfort .consider, back up rim on inside of aperture. epoxy flange of 11/4 x 1/4 strip. drill and tap same holes. Could do the same with cover plate too. Avoid any chance of warping /slopping of fuel slamming around inside.

 

Meh, the screw setup has been doing an okay job so far, it seems. I'll improve on it if I find it causes a problem later on. There's a good amount of screws around the perimeter, so each one of them is probably not seeing a lot of force.

 

With the cutout on the side of the tank, I’d use both gasket and sealant (on both sides of the gasket). With thin threads in aluminum, you can’t snug down on the gasket very hard.

Daily polishing is a bit of overkill. Are you using the engine pickup tube for this? If so, you rarely get anything that settled to the bottom anyway. They are usually designed above the bottom, to avoid ingesting contaminants. Fouled tanks pick up bits when rolling around at sea. The biocide should keep the slime away. Some people like putting a desiccant filter in the vent line and/or add water treatment (but don’t use an alcohol based treatment). I use DESL-SHOK from USA Fuel Service. Don’t overdose this either.

Polishing is also done with smaller micron size filters than one would typically use for their engine primary filter. I like the idea that you’ve plumbed for polishing, I’m just not sure it’s practical on a daily basis.

 

polishing every day is a bit ( lot of ) over kill. you just cleaned the tank so you are good to go for another 10 years. with a 500 filter you would have to run the engine every day all day to dirty the filter in a year. good for 60 GPH for every day all day use.