1974 170 fuel tank

[shvr_me_tmbr]

We decided to tackle the fuel tank today. When we bought the boat the previous owners were using a portable tank. When taking the tank out we noticed no one had ever resealed the hatch with any silicone so when we got the hatch off the tank was floating in water. We haven't scraped away all the foam yet but we didn't see a drain for the water to go anywhere. Is there supposed to be one or should we just make one? Also the tank has some pitting but does not leak. We plan on using epoxy or jbweld to fix the current pits in the tank. Does anyone have any advice on what they have done? We are also going to replace the sending unit. Is there a particular brand that works better than others?

[Capt. Bob]

OK,
Having replaced only two tanks, I'll give you my opinions only, no advice.

One, aluminum that has water trapped against it for long periods is toast (opinion based on experience only).

Two, repairing aluminum I'm sure is done all the time but I'm not the guy so... corroded in just "some spots" is a flag to me indicating time to replace (again opinion based on first hand experience not fact).

Three, I'm for playing "risk to reward" scenarios in my life and leaking fuel has no known reward to me so......

 I would clean out the tank coffin, replace the tank with a new one (alum or poly) and move on. Your installation technique is personal but we have several different types here. The key to extending an aluminum tank life is protecting it from prolonged contact with moisture. In its natural state, aluminum will provide an excellent corrosion barrier but it must be kept relatively dry. Again just my opinion based on personal experience.
PS...  A WEMA brand (reed) fuel gauge....

 (http://www.wemausa.com/sensors/level-FuelWater.shtml#.VL2dmC6jCjw)

 Is the most popular choice among members like myself running a mechanical type.

Good luck.

[fitz73222]

Ditto what Bob said, fixing a pitted aluminum tank is not worth the risk... Replace it. As far as drainage goes, I'll give you an example. My tank on my '73 22-2 was replaced in '94. This weekend, I pulled the hatch to replace the fuel lines that have been there since the tank was replaced. The hatch was sealed very well with silicone sealer. When I pulled the hatch the fuel tank is still like the day it was installed, the hatch still like new with zero rot, the foam surrounding it, bone dry. Even the fuel line still looked new, but 20 years is way too long on a fuel line so I had to go in. The point is if the hatch is sealed correctly, the tank will last indefinitely.