Treating inside/outside of gas tank with POR15 products and removing evaporation tank

[Jusjofok]

Thanks for the inspiration Dogma420!

I just did this on my 240 this past weekend. Made a few changes though. Instead of soldering on a cap on the vent line on the left side I used a copper pipe cap that fit snugly inside a short piece of 5/8 fuel line, clamped it in place. On the upper end of the vent hose where it connects to the fuel filler neck I used a barbed PVC fitting that was 3/4 inch on one side and 5/8 inch on the other, I trimmed off a couple of the barbes to make it similar in length to the old white plastic tube, this works perfectly and you can't even see it when its all together. The other differnce from the thread above is I didn't use the copper 180 degree fitting compilation, I merely left quite a bit of slack in the vent line so it made a nice loop with a rather large radius. Seemed to have plenty of room for a nice kink free loop. So far it has been working well, fuel fumes in the cabin appear to be at much more tolerable levels.

Thanks again,

Justin

[AT-JeffT]

Hey Dogma420,

Mind sharing what it cost you to have the tank boiled? Thanks.

[Mike B]

Hey Dogma420,

Mind sharing what it cost you to have the tank boiled? Thanks.

Dogma is not on the site much any more, so he may not even see your post. His profile says the last time he was here was on 10/21/09.

I haven't had a gas tank boiled, but I had a radiator done and I think it was about $100 and a gas tank would probably be similar.

-Mike

[jmortensen]

Anyone had problems with gas expanding and pouring out the filler with the expansion tank removed? Asking because of comments made on this thread:

http://forums.hybridz.org/index.php/topic/95827-replace-plastic-expansion-tank/page__gopid__902347#entry902347

[Duffman]

I did the expansion tank removal, gas overflow goes from the filler neck back into the tank, which is where the connection is now made from the filler neck. There is no gas spilling on the ground, ever.

[Carl Beck]

Hi Jon:

First - it is not an "expansion" tank nor an "overflow" tank - it is a gasoline vapor recovery tank. You can tell that because it is mounted higher in the car than the filler neck. If it was an overflow tank, it would be mounted at or lower than the filler neck. It's sole purpose is to contain gasoline vapors within a closed systems, thus preventing them from venting to the atmosphere, until they can be either condensed back into liquid form where they drain back to the tank, or sent to the engine to be burned.

Gasoline vapor control started in California {CARB standards} and was required for new cars sold there in 1970. I do not know if California required that system earlier than 1970, but it is possible they did. The Fed's added the requirement to the Federal Emissions Standards for all 50 States in 1971.

Early cars sold in Canada in 1970 did not have it, nor did they have the air injection systems required in the US. Sometime after March of 1970 - Nissan started producing all 240Z's sent to North America with the same standard emission controls so Canada got them, necessary there or not.

The earliest 240Z gas caps were the vented type {many 240Z's produced in 1969 did not have the vapor recovery systems at all} - which allowed gasoline vapors to escape when the gasoline in the tank expanded from heat, and allowed air to enter the tank as gasoline was pumped out of the tank, or contracted with cooling. With the sealed evaporative emissions control system, vapors are collected in the vapor recovery tank, and vapors/or liquid is pushed to the engine crankcase {then vented into the intake manifold by PCV valve}; when contraction occurs air is drawn into the tank from the air cleaner. This is controlled by the Flow Guide Valve on the left front inner-fender.

If you eliminate the gasoline vapor recovery system - to eliminate the possibility of gasoline vapors escaping into the passenger cabin - then you should also make sure your gas tank cap is vented. This is most important - as failing to do so can give the symptoms of a weak fuel pump or vapor lock. The fuel pumps on the L24 are capable of pumping liquid from the tank, to the point that the tank can collapse. The fact that it doesn't happen often has to do with the old gas caps failing to seal as designed when new. If you are unlucky enough to have a really good sealing gas cap - then you'll see the symptoms mentioned above.

Someone - some time ago Posted pictures of both types of Z gas caps on the Web. Someone else Posted pictures of his collapsed gas tank as well.

FWIW,

Carl B

Edited October 26, 2010 by Carl Beck

[jmortensen]

That makes sense Carl, thanks. I also looked and found some stats on gasoline expansion, and the estimates varied, but I did find one that said 375 ml on a 20 gal tank with a 15 C temp change. Since the tanks are underground they are somewhat insulated, and that apparently is the standard temp difference for checking pumps to make sure they deliver enough fuel. 375ml is about the volume of a coke can, so unless you filled up right to the very top on a cold night and lived next door to a gas station, I'm guessing that you just wouldn't have a problem.

[EScanlon]

Tony D's comments on Hybrid Z are a good example of predetermining the validity of something before you read the document.

His statement:

The purpose of the (expansion) tank is to allow for some place for the fuel to go with an absolutely full tank...

is in error. The purpose of the expansion tank is for the fumes from the gas tank to have a place to condense whereby they can drip back into the main tank.

With the expansion tank (aka evap tank) being higher than the filler neck, engine and generally the rest of the car (it's located about the same level as the quarter windows) it would take a great deal of expansion for the gasoline to even reach the lower level of the tank.

I presume he just imagined that the overflow vent line went nowhere:

It vents the filler neck to the ground. So if you fill up, the gas simply overflows on the ground by your right rear tire. Wonderful!

The filler neck overflow tubing goes to the rear and uppermost vent (5/8") on the tank. The forward and uppermost vent connects to the diverter valve and the two right by the sender opening go to the carbs and back. There are no lines venting to the ground.

But his line of:

if the expansion tank was not needed, then why wouldn't Nissan leave it off?

forgets that automobile manufacturers were REQUIRED to incorporate those tanks as part of the emissions systems.

Beandip has this same arrangement in his car. Give him a PM and ask him if he's had any problems with overfilling. That way you'll get it directly from someone that can give you first hand knowledge as opposed to an arm chair evaluation of the system.

FWIW

E

[jmortensen]

Tony D? Confirmation bias? Surely not!!! ;-)

[jmortensen]

In arguing with Tony I did find one thing that I think he is right on. That line that goes to the front should not be routed the way it is in the OP's post. If you have a full tank and park on a hill for example, I think it would be fairly easy to have gravity drain the tank into the crankcase. All that would be needed would be to get the tank vent higher than the outlet at the front of the car. If I recall that tube correctly it comes out on the driver's side frame rail and goes up to about mid fender height where it connects to the crankcase breather tube. If that recollection is correct I would suggest plugging it at both ends or running the vent to the filler neck and plugging the tube at the front.

[Carl Beck]

Hi Jon:

As connected in the OP's diagram - all you need to do is plug the Flow Guide Valve {FGV} port that would otherwise connect to the crankcase. You can leave the port that draws fresh air from the air cleaner, to prevent forming a vacuum in the tank - as the check valve in the FGV only allows air intake and prevents flow of vapor or liquid out to the air cleaner.

If you eliminate the vent line - by plugging both ends of the line - then you have to drill a hole in your gas cap to allow air into the tank as the fuel level lowers.

FWIW,

Carl B.

[argniest]

Does anyone know what part number for the fuel filter he was talking about, for a clear fuel filter. I would like to buy one and put it on the car, so I can help determine how much junk is coming out of my fuel tank. Its pretty cold out here for a while, and I am not sure if I want to mess with the fuel tank quite yet. but If I could put a clear see through fuel filter on there, at least I could watch if a bunch of junk is truely headed from the tank or not!!?? Thanks