Vapor Tank Question

[Zed Head]

On 5/21/2024 at 12:58 PM, HusseinHolland said:

What I wasn't expecting was actual fuel in that metal vent line coming up the inner fender. When I pulled off the hose there was fuel all the way up at the hose.

Vapor condensation?  It's what they do when they get cold.  Vapors.

[HusseinHolland]

12 hours ago, Captain Obvious said:

Have you made changes to the way your tank venting is done? Anything other than replacing failed / leaky hoses?  I don't remember what you have done back there. 

And I think you are supposed to have the "check valve" device installed in the vent line running from rear to front. You're saying you don't have one?

I have made changes - I removed the vent tank, ran. the 5/8" filler neck hose directly to the tank fitting, and ran the 1/4" vent line directly to the charcoal canister hard line bypassing the vent tank. That was all after finding the liquid fuel in the line though. 

There is no check valve that I can see between the vent hose, hard line & charcoal canister that I can see, unless it's tucked up above the fuel pump mount bracket where the vent hose clamps to the hard line, which I doubt. 

[Captain Obvious]

When you get gas, do you top off the tank to the very top or something? Just looking for theories.

[HusseinHolland]

6 hours ago, Zed Head said:

Vapor condensation?  It's what they do when they get cold.  Vapors.

Seems plausible in theory. I wouldn't expect there to be enough vapor to fill the vertical hard line off the rail up to the canister though. I'll pull the hose off the hard line  after a few tank fulls & see if it reoccurs. 

[HusseinHolland]

19 minutes ago, Captain Obvious said:

When you get gas, do you top off the tank to the very top or something? Just looking for theories.

I insert the gas filler nozzle completely , and stop when the nozzle check shuts off supply. I don't keep adding after that. I also had never filled the tank prior to fixing the original ruptured vent hose a couple weeks back. 

Edited May 24 by HusseinHolland

[Zed Head]

Here's an image from the 1991 300ZX FSM, just to look at.  No vent tanks, just straight lines.  And a check valve.

[Zed Head]

13 minutes ago, HusseinHolland said:

I wouldn't expect there to be enough vapor to fill the vertical hard line off the rail up to the canister though.

Have you seen distillation in action?  Vapor moves man!

Actually, the hotter the tank is and the colder the line, the faster you'll build up liquid.  I'd actually be surprised if condensation was not happening.

[HusseinHolland]

22 hours ago, Zed Head said:

Here's an image from the 1991 300ZX FSM, just to look at.  No vent tanks, just straight lines.  And a check valve.

 

22 hours ago, Zed Head said:

Have you seen distillation in action?  Vapor moves man!

Actually, the hotter the tank is and the colder the line, the faster you'll build up liquid.  I'd actually be surprised if condensation was not happening.

Thank you - I'm second guessing whether removing the vapor tank has caused the problem - however I don't know of any other car that had such a contraption, and the later Z's don't have it, so it would seem something else is the cause. I filled the tank yesterday afternoon. Today, the car was in the sun all day & early evening I drove around for 5-6 miles at low speed (25 mph zone, heavily policed) with the Mrs, and the we got home & she got out, she could smell raw fuel. I turned it off & could see gas dripping out the charcoal canister base, running down into the splash pan(!) I could add a check valve, but that wouldn't alter fuel/vapor running from the tank to the canister.

I can reposition the vent line at the tank, so it runs elevated relative to the 5/8 vent, right now it angles downward off the tank nipple.  I'll add the vent tank back if I have to, just rather not.

 

diagram

Edited May 25 by HusseinHolland

[Zed Head]

The purpose of the tank on the early Z's might have something to do with the position of the hoses.  The fuel probably sloshes pretty hard on turning, pressuring the vent lines.  Without the tank that fuel could get pushed in to the vent line to the canister.  The way that the system is illustrated suggests that it has a "drain-back" purpose.  Plus they called it a liquid/vapor separator (#3).

I'd guess that the vapor hose entry points were repositioned in later tanks.

 

p.s. I'm not sure I was following what you were reporting in your previous post about liquid in the line.  I thought it was with the #3 tank in place.

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Edited May 25 by Zed Head

[Captain Obvious]

1 hour ago, HusseinHolland said:

I drove around for 5-6 miles at low speed (25 mph zone, heavily policed) with the Mrs, and the we got home & she got out, she could smell raw fuel. I turned it off & could see gas dripping out the charcoal canister base

That is clearly not the way things are supposed to work and the first thing I would do is put the vapor tank back in.

Only thing that confuses me is you said you were getting liquid in the vent line even before you took the vapor tank out?

23 hours ago, HusseinHolland said:

I removed the vent tank, That was all after finding the liquid fuel in the line though. 

So you were getting liquid in the vent line with a stock configuration vent tank and hoses?

[HusseinHolland]

11 hours ago, Zed Head said:

The purpose of the tank on the early Z's might have something to do with the position of the hoses.  The fuel probably sloshes pretty hard on turning, pressuring the vent lines.  Without the tank that fuel could get pushed in to the vent line to the canister.  The way that the system is illustrated suggests that it has a "drain-back" purpose.  Plus they called it a liquid/vapor separator (#3).

I'd guess that the vapor hose entry points were repositioned in later tanks.

p.s. I'm not sure I was following what you were reporting in your previous post about liquid in the line.  I thought it was with the #3 tank in place..

I see that it is described that way - but it appears in practice that the drain back feature seems implausible, given the height of the 5/8 fittings on the upper side of the vent tank - it would have to be full of fuel for that to happen

 

11 hours ago, Captain Obvious said:

That is clearly not the way things are supposed to work and the first thing I would do is put the vapor tank back in.

Only thing that confuses me is you said you were getting liquid in the vent line even before you took the vapor tank out?

So you were getting liquid in the vent line with a stock configuration vent tank and hoses?

 

Yes, to be clear there was liquid in the line at the charcoal canister with the vent tank in place - I could smell the fuel at the original connecting hose - which had cracks at the canister end. which is why I didn't think removing the vent tank would make a difference in that regard. What I experienced today was a deluge out of the canister - quite a different story from a little liquid sitting in the line.

EDIT - to add to this - Prior to fixing the ruptured 1/4 elbow hose at the tank, I had only filled the tank once - which was how I discovered the leak at the tank - after that I had not ever filled the tank beyond 1/2 full. I do not recall getting a gas smell at the charcoal canister, and since the vent circuit was open at the tank, that would all make sense.

Timeline: I "fixed" the hoses at the back, leaving vent tank in place.

After that, in checking the overall system,  I noted fuel odor at the charcoal canister. Drove 500 miles to Carlisle PA & back. No evidence of fuel vapors.

Fuel smell developed in cabin .

Decided to bypass the vent tank.

Replaced the short hose from vent pipe to canister. Noted liquid fuel in vent pipe at charcoal canister. Swapped out Nissan Canister for Volvo Canister

Still had slight fuel smell in cabin - - which was the improper (permeable for fuel) 1/4 hose I ran from the gas tank to the vent tank

Reroute new 1/4 vent hose beneath. Fill tank. Fuel subsequently drips from charcoal canister.

I'm going to have to put everything back to stock configuration & see if there is liquid fuel in the line with a full tank of gas after that.

The way I have it now, the 1/4 vent line is below the level of the vent to the filler neck. The factory setup has the 1/4" vent line as the highest point in the system, above the filler neck vent. The 5/8" and 1/4" vents also combine at the vent tank. I have them completely separated.

With a full tank, actual fuel must be sloshing into the 1/4"  line.

 

Edited May 25 by HusseinHolland

[HusseinHolland]

OK - I'm cautiously optimistic about the revised setup I made today. Pondering the factory diagram, and those of the several generations of Volvos I have owned, I surmised that my main mistakes were:

1) running the 1/4 vent hose below tank level

2) separating the 1/4 and 5/8 circuits.

So, in my continued effort to NOT put the vent tank back, I revised the 1/4" vent line to connect with the 5/8 line. This way, if any quantity of liquid either makes its way up into the line, it will drain back into the filler neck connection, as it would with the factory setup. The 1/4 vent then continues in a loop, and goes back out to connect to the factory line up to the canister. The underside of the canister was still damp with fuel from the prior setup, however after I wrapped up & drove around for a bit, went to Home Depot, left it sit, came home, the canister was emptied of fuel condensate (bottom of canister felt dry to the touch). I'll check it again tomorrow before I reinstall all the hatch trim.

Tank end, elevated the vent hose

elbow coming out of cabin

Tool for installing these fittings, makes it much easier

4 way connector is from a Volvo tank vent setup

Edited May 27 by HusseinHolland