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Drill hole in ss tank


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Had the same issue. My thought was to cut a disc out of 5mm stainless plate, drill and tap the centre and then affix to the tank with pop rivets with either a rubber gasket or mastic in between. Didn't do it though so don't know how it would pan out in practice.

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A length of dowel never lies, corrodes or stops working for some mysterious reason.

 

That what I had in my last boat

 

Currently have fancy electronic gauges and at best, they are a rough indication as tanks are never square and level so gauge doesn’t move in true relation to usage. I work on 3/4 being half, 1/2 being quarter and 1/4 being time to refuel

Possible a bit harsh but in all reality I trusted dipping the tank more.

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No way here of finding fuel quantity.So want to do something about that. For dipstick I need to cut a hole. Tho mate said just seal on clear piece of perspex seethru does the job. Maybe look at rivets? Then best way to seal,gasket or a sika?

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Oblong hole.  Make the flange for the inside with welded studs that pass through the tank from the inside and then bolt through an exterior plate. The exterior plate will have the tank sender mounted through it.  Might sound complicated but it is pretty simple in practise.

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We've moved from a calibrated old sail batten to an electronic gauge with our most recent change in boat and I'd trust the dipping the batten option more. Now use the assumptions Jon describes.

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I fit a few gauge systems. Symmetrical tanks are easy. If you use a pressure sensor with a probe, top mounted is easiest. Fill the tank. Drill/cut the hole. Tap the bolt holes. Its best if you can remove the unit in case of failure. Then insert the tank spear into the tank, right to the bottom. Mark the spear at the top of the tank. Withdraw it and cut to the right length, 10mm shorter than the marked length. Now mark 1/2 way, then  1/4 and 3/4. Put the sensor on the spear, insert 1/4 of the way in, calibrate 1/4 on the gauge. Then 1/2 way, then 3/4 and right installed. Done. Easy.

 

If it is not a symmetrical tank, best to know the capacity, start with an empty tank, calibrate as you fill. Harder.

 

I usually use smartswitch tank monitors. 

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If I understand the original question correctly, the problem is the thin metal of the tank. There are several ways to do this.

 

Simplest is using self tapping screws and simply screw the sender unit directly into the tank. Use a sealant suitable for Diesel, between the flange and tank. Because the Fuel will mainly be splash rather than submerged, self tappers should provide plenty of grip

The best way is a lot more work and best if the tank is removed to do this. A bit of fiddly and exacting work is required.
Use Rivet Nuts. These are a Nut that the head "forms" and is rolled over the tank metal. Then you simply bolt down the sender using either a gasket or a sealant between.

The third way is not really used in this situation. It is used when some pressure is involved, such as the fitting being mounted or permanently submerged at the bottom of a large tank. I won't go into in great detail, but it uses a split bolt flange. The Bolt flange is cut and spread slightly to make it look like a spring washer. It is fed into the tank and then held in place. Sometimes a couple of small counter sunk screws pull it up into place and holds it till the main bolts are torqued up.

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I put a mechanical fuel gauge on my tank same issue re fastening to a tank wall about 1.5mm. I used self tappers pan head with a fibre washer under each head and plenty of sealant under the housing. It's been over 15years and no issues. The key is a washer or o-ring under the screw head.

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No do not use RTV products. Although there is a Black RTV gasket sealant that is Oil resistant. But it should not be used for contact with fuel.
There are many specialist products available for use in Fuel contact situations. For instance, Permatex has a large range of products. Although one could argue the range is too large. It gets confusing trying to work out which is the best choice.
https://www.permatex.com/product-category/gasketing/?fwp_per_page=48
 

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