Old steel Evinrude tanks venting question

[SteveVT]

I have three old Evinrude steel tanks with internal bubble fuel gages that I got with my '63 Lark V. They're in good enough condition to use, but they don't seem to have tank vents, unless they were covered up with red paint by the PO. I scraped the fuel cap clean of paint, but I still don't see how they vent, unless you intentionally leave the fuel cap partially open.

So were they supposed to be non-vented?

These were tanks for a vacuum type fuel pump, not a pressurized tank system, I believe. Single line.

Pressure does build up pretty heavy on a sunny day, and I'm wondering what it does to the fuel pump diaphragm, and float valve with that much pressure buildup.

I've already learned the hard way that before disconnecting the fuel line, I have to open the gas cap to relieve pressure or before the quick connect check valve closes there's a quick gas spray.

I did notice that one of the fuel gage hold-down screws is labeled "drain". Not sure what that's for.

So are these tanks correct without vents?

Thanks!

 

[jimmbo]

Those tanks vent when the hose is connected. On the tanks fuel connector there are little silver pins sticking out, those pins open the vent valves.

 

[RCO]

The o-rings in the sender are almost always bad on those tanks unless they have been changed before. Best to buy a couple new o-rings and core plugs if you plan on using them. The drain screw is to drain the tank by removing the screw and holding the tank upside down. You can't drain it completely through the filler cap because there is a collar that is lower than the top of the tank to prevent overfilling.

 

[SteveVT]

Thanks jimmbo, RCO!

I wondered what those silver pins did. Now I know.
Will check and replace O rings.

 

[Scott Danforth]

o-rings are about $0.030 each. takes about 5 minutes to change once you remove the fitting from the hose, knock the plug out, etc.

 

[jimmbo]

He said the tank was holding pressure and only spray fuel out for a sec when line is removed. Sounds like the O-rings are working fine

 

[clemsonfor]

But if connected it vents why would it be under pressure and spray out when disconnected?

 

[jimmbo]

I was basing it on it spraying as the fuel line was being connected. Good catch:embarassed:

 

[Chinewalker]

It vents throug a check valve. Only allows air in as fuel is drawn out.

 

[SteveVT]

Okay, thanks guys, but I'm a little confused now.

When engine and tank are connected and the sun is out, pressure builds in the whole system. This is without the engine running.

If I disconnect the hose at the engine, fuel sprays out for a second while I work the connector off (it's a little tight- and probably that's due to pressure and the seal - as a guess).

Once it's disconnected at the engine (not the tank) no more fuel comes out. But the hose and tank are still under pressure. If I open the fuel cap pressure releases.

If the pins are supposed to allow venting, they aren't doing their job, because the pins are in the tank fitting, and the hose is still connected there.

So are they working properly or not?

 

[TN-25]

I always thought that you had to crack open the fuel filler caps to the first stop to get them to vent on the metal 6-gallon tanks. Also the early 3 gallon tanks (1968 - mid 70s) had a vent disk but it was eliminated on later metal versions.

 

[clemsonfor]

It sounds like it's working right after reading these guys descriptions. See post #10

 

[SteveVT]

TN-25 okay, but didn't realize that was normal procedure.

Mention of the pins as a venting mechanism seems to say that cracking open the cap wasn't necessary.

clemsonfor, I wrote post #10. The question was how these tanks are supposed to vent, not how they are supposed to seal.

 

[Chinewalker]

As I mentioned in post #9, the check valve is in place on the underside of the fuel fitting to allow air in. It does not allow air out, whether the pins are depressed or not. These tanks don't "breathe" like the old screw-vent style tanks can where the free flow of air in either direction can allow accumulation of condensation on the inside of the tank. They can still get damp air in there, but you don't get the cycling you would on a freely vented tank. As others have mentioned, it sounds like your tank is operating just fine.

 

[SteveVT]

Okay, so then it's fine if high pressure from sun builds up in the tank, lines, pump diaphragm and float needle and I shouldn't be concerned about them at all, because that's how it was designed. Correct?