My Gen.2 -Now only holds 31/2 gallons of gas in the tank bladder

All sorts of plumbing/pressure/vacuum action going on in this system. I guess it follows that it isn't fully instrumented electronically.

Consider the mechanism within a gas station nozzle. Nothing electronic in its operation, yet lots of intricate logic mediated with tubes, balls, cones, springs, and diaphragms responding to gasoline and air flow.

After years of experience with the 2nd generation Toyota had the option of either adding electronic sensors and actuators to make it easier to control/diagnose the gas tank and evap system, or to go back to a regular gas tank without the bladder, and they chose the latter.

 

The automatic shut-off nozzle was apparently invented in Vancouver, named after the guy, the Seney Valve. My wife was doing home support for him. There maybe were others, collaborators or independents.

 

Compare and contrast, Japan vs. USA gas tank diagrams from Amayama (the year ranges overlap but are not identical):



There are actually two schemas for the USA model that differ slightly. The final schema for both countries seems to be the fuel line from the tank to the front and is virtually identical - the parts listed for that schema are the same but you can see that the routing of the tubes from the canister and fuel pump above the tank are a little different.

Not even the charcoal canister is the same part for both countries. 77740-47040 vs - 47050.

 

The ORVR system for gen 3 is a lot like gen 2, except for the bladderless tank. There still isn't a lot of instrumentation of the ORVR components, so it's still largely up to the human to diagnose issues.

 

Prius Hard to Fill Fuel Tank – Diagnostic Network

I don't have an account there, but it might be that the answer is available in one of the 3 blurred out replies if one does.

 

Finally decided to join the forum to share some info. I was able to swap the gas tank out for a carolla tank and just did a 100 mile test drive with mixed driving and no check engine lights or issues.

I'll be making a video and post of what I did after I get a full tank out of it to help others if they want to attempt the swap. It's not as easy as one would think. I'll say that.

 

I'm curious to know why you do this?

 

I knew it would go I'm just not sure about pressure sensor etc but getting it in they're seems to be a few that could strap in . I'd like to work in plastic unit . Easier to have custom fabbed too. But I'm making so many miles by the time I do this the car will be dead by well 600k or such . So I've not . But yes write it up pictures and year models for the parts or list.

 

Out of habit. Our state historically was one of two which mandated your gas must be pumped by an attendant. You'd pull up, wait a while until an attendant takes your card to activate and start the pump, they walk away, the pump stops, then you wait until they return to finish the process. They were paid by the hour and not by how many cars they filled. So I sat in the car and out of boredom kept the key in the on mode to make sure the fuel gauge go full before it finishes. I also log the mileage and the odometer display only worked in the on position.

 

Change the charcoal canister too? I've read that the one on the Prius is pretty small because the rubber bladder handles most of what the canister does on other cars.

I don't really understand in detail how the bladder decreases evaporation. It is always presented as "no air over the fuel to evaporate into", which makes some sense because one of the rate variables for evaporation is surface area at the gas/liquid interface. Molecule hits interface from liquid side and if it has enough energy it can break through into the gas phase, more area, more that happens. If there is no gas phase to break into, lower evaporation rate. However, some gas is eventually going to form above the liquid and it would seem like the bubble would just get bigger and bigger until the pressure increase from its expansion causes the evaporation to stop (or the tank vents or blows up). So the bladder is probably designed to let these bubbles rise to a vent and bleed off this small amount of gas through the canister. Also, the pressure inside the bladder could be higher than atmospheric (rubber container after all) and that would also reduce evaporation. Many conventional gas tanks seem to do something like that, since they hiss when the cap is removed.