Need to replace gasoline tank sending unit. Tank has odd hole pattern.

[Bryanbt]

I would like to replace the sending unit on the gas tank for my A4 on a 1971 C&C 30. Tank is Monel and original to the boat. Old sending unit is dead and is the standard 5 hole model. Problem is when I remove the old unit I find it was mounted on a plate with 10 holes all drilled through.
1. What type of unit should I use to replace the old one?
2.How do I ensure none of the holes leak?
3.Will a standard "5 hole" model plus the gasket be enough to seal all 10 holes (as apparently the old one did) ?
4. Would I need to use some sort of gasoline resistant sealant between the gasket and the tank?

Photo attached.

https://goo.gl/photos/GnXXfuyRFC27HoR18

[tenders]

If the old unit worked with a gasket, I would not hesitate to assume that a new one would work with a gasket. Sealant and stuff runs the risk of getting into the tank.

You might find the new sender works erratically with the old gauge. Consider replacing the gauge too.

Monel tanks are the gold standard, as I'm sure you're aware. My boat went through a steel fuel tank every twenty years, like clockwork. Now that I have stainless it should be good for another sixty years or so.

[ndutton]

A long time ago fuel gauge senders were installed with cork gaskets and a sealant like Permatex. I would think the combination would work well for this application too.

[Bryanbt]

Thank you tenders and thank you Neil.
This is my second attempt at this task since I have owned the boat. Originally the unit did have a cork gasket and as far as I know it did not leak. My first replacement, using a rubber gasket did not work well as there is still some seepage with a full tank and especially if the vessel is heeled to starboard for some time. My strategy has been to keep the tank below 3/4 full at all times.
I had not considered trying to find a cork gasket. I think that is worth a try. I will report back if I find one and it works.

[ndutton]

You'll probably have to make your own. Generic gasket material kits include a sheet of reinforced cork. Please consider using a sealing gasket adhesive too.

If it were me I'd do a 3 psi pressure test of the repaired tank, a test that's USCG required. It's a little involved but a sure fire (vernacular unintended) and safest way to know your tank is leak free. Post back if you're interested and we can discuss further.

[thatch]

Bulk cork gasket material is available at virtually all decent auto parts stores and, as Neil stated, would be the best choice for this application. The trans cover is also cork and, at .060" thick, has good gap filling properties. While switching to a Moeller tank a few years ago I used cork for the top fittings and there have been no leaks. A hole punch set is available at Harbor Freight for about $5. Cork material is easy to work with and can be easily cut with scissors or Exacto knives. Lastly, I photo-copy and print all factory gaskets full size and have the material type and thickness written on those pages so that I can duplicate them immediately without having to wait for the mail to bring a replacement.
Tom

[joe_db]

JBWeld the extra holes???

[marthur]

I wouldn't worry about the extra holes, I would worry ab out getting a good gasket on. My aluminum gas tank had them too. The 40 year old rubber gasket did a great job of sealing them right up until it was replaced. The new rubber gasket did just as well. Funnily enough, I usually make a cork gasket (as previously suggested) for this type of application.

Not sure why they were there, but it did allow the sender to be in almost any orientation.