Replace plastic expansion tank

[The Crusher]

I need to replace the plastic expansion tank in my 71. I have a metal one out of a 72-73, but it is a little bigger/wider and does not bolt right in.

Has anyone else tried this. I am looking for an easy way to do it without a lot of cutting involved. I could use a hammer but there has to be an easier way.

[JMortensen]

I beat one up with a hammer. There is a write up on www.classiczcars.com that involves hooking a couple of them together and attaching to the hole in the filler neck. and not using the tank at all.

[The Crusher]

Thanks for the reply. I guess I'll try the hammer. Someone else told me to use a hammer too, but I was hoping for something a little cleaner. Thats ok, it will be covered up any way, I just want to get rid of the gas smell from my old tank. I just put all new hoses on and the tank is the last thing I need to change.

[Tony D]

How clean do you want it to be, do you plan on running around with the plastic covers in the back of the car removed? Nobody will ever see it. Get the hammer. A big one. Make it conform unmercifully. (See related post "Are we too Cocky?" in Non Tech... )

[JMortensen]

You might take a look at the classiczcars.com idea, and consider just getting rid of the thing entirely.

[Tony D]

Where does the expansion of liquid go on a cold morning fillup to 'full' without an expansion tank---overboard? Or is the crankcase diverter valve left in place and it just dumps into the oil in the crankcase?

 

Or after elminating it, do you just not 'fill full'?

[JMortensen]

I don't know the answer to that Tony, but I can't think of another vehicle I've owned that had an expansion tank, so maybe it just isn't that necessary. Here is the thread on classiczcars.com, makes no mention of not filling up all the way: http://www.classiczcars.com/forums/showthread.php?t=19034

[Tony D]

"but I can't think of another vehicle I've owned that had an expansion tank"

 

I can't think of one post-67 vehicle in the USA that doesn't have one(obviously my 62 VW Bus, 60 Corvair, 66 Corvair, and 66 VW Bus don't have any, they predate the legislation!) Pretty much most cars since 67 were mandated to control and make captive evaporative emissions. The Charcoal Cannister in any 75-on vehicle performs this function. Before that point in time, there were several allowable EVAP containment scenarios allowed. The 69-73 Datsuns many times used 'phase separation' (the tank) and 'Crankcase Accumulation' if you had any other Datsun 67-73 you had a car with a tank. Almost any car after 74 had a Carbon cannister for both expansion and evap control.

 

The purpose of the tank is to allow for some place for the fuel to go with an absolutely full tank (supposedly it's 10% of total volume, I don't know maybe they count the 15mm hose volumes in that as well...) so that ONLY vapors go to the diverter valve on the left inner fender, and on into the crankcase for accumulation.

 

That someone does something doesn't mean they did it right. I'll have to check out the thread. This may be interesting!

Edited October 20, 2010 by Tony D

[Tony D]

Yes, that modification will not pass integrity testing. 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!

 

No thanks, for the 15 or 20 minutes of putting some adapters on there, and running smaller fuel lines I'll retain my evap system so it doesn't dump raw, $3.00 a gallon gas on the ground after a fillup on a cool morning while the car stays parked in the lot outside work.

 

Get hit from the rear in that car, PRAY! It's a Pseudo-Pinto waiting to happen!

 

As I said, 'just because someone does something doesn't mean it should be done!'

[theghosttanker]

So here's a related question for ya Tony (and whoever else). I'm building a '73 with a megasquirted 2.8 liter and using a '75 fuel tank.I want to keep the engine compartment as clean as possible. How would you recommend hooking all the stuff up/ I have both a plastic and a metal expansion tank available.

[cygnusx1]

 You can calculate the size of the expansion tank that you will need, with the following info.

 

API factor for gasoline is about  0.00069/degreeF

Edited October 26, 2010 by cygnusx1

[JMortensen]

I think the overflowing on the ground thing is a bit overdramatic. I suspect you'd hear a bunch of people complaining about this happening if it had been a problem.

 

Ghosttanker, forget the plastic tank. I cracked three of them before I beat the hell out of a metal one, then never had another problem.

[Tony D]

Well, my car does it...

What's your source for arguing it won't happen---if the expansion tank was not needed, then why wouldn't Nissan leave it off?

 

Why, on cars WITHOUT the tank did they have a 5mm line in the filler neck vented to the atomsphere (wanna guess what happens when you fill the tank cold and then let the car sit in the sun...two guesses, first one doesn't count.)

 

Seriously JM, how is this a point of argument or dispute? Are you seriously contending that gasoline does not expand and contract by volume when the temperature changes? The tank is there for a reason. If you are content to short fill your tank to 11.7 gallons and leave 10% for thermal expansion every time then fine...

 

But if you fill that tank to the top of the filler neck and put the cap on some cold morning...and the sun comes out later in the day...

 

Well, there are PLENTY of Z's with gasoline stains from a leaky tank...and I have seen more than one overflow from thermal expansion when filled in this way.

 

Aircraft support equipment, too!

 

Sometimes, I think you dispute things just because you can. Where's the logic in your rebuttal 'because we haven't heard about it, it's not a problem'...well how many people do you know that remove the expansion tanks? Maybe you don't hear about it because people replace the vent hoses and don't hack-job a shadetree 'fix' into their car incorporating plumbing supplies and JB Weld.

[JMortensen]

Tony, I really do not argue just to argue. I argue because I want to find out the REAL answer. I think you get really frustrated when people don't just take whatever you say as gospel, and I'm really sorry if me not believing everything you write offends you.

 

The Z has a 16 gal tank. Not sure where 11.7 gal comes from. So if you were allowing for 10% expansion, you should be able to fill to ~14.5 gallons, right? The problem is that I think that 10% expansion is vastly overstated.

 

Gas stations have underground tanks, which makes them less likely to have a huge swing in temperature from morning to night. The gas is going to come out at a relatively stable temperature in comparison to the ambient air temp. So on a hot day it will be cooler, and on a cold night it will be warmer than the ambient air.

 

http://www.associatedcontent.com/article/669765/buy_cold_gasoline_and_save_money.html?cat=27

So knowing all of that just how much does the volume of a gallon of gas change with a day-to-night temperature swing? To make this calculation, I'll assume an nominal day-to-night temperature change of 30 degrees Fahrenheit, and, as found in a wide variety of sources; use the value of 0.000528 per degree Fahrenheit as the volumetric coefficient of thermal expansion for gasoline. Multiplying these factors together yields a volume change of 0.0158 gallons per gallon or, in a measure that makes sense, a volume change of about four tablespoons per gallon. In a car that gets 20 miles per gallon, this would mean about an extra 1/3 mile per gallon (a 1.5% gain).

 

While the article is talking about getting better mpg out of cold gas, the expansion is useful for our discussion. In a 16 gallon tank, you're looking at 64 tablespoons of gas, or 1/4 gallon for a 30 degree change in temp. Now if you don't live right next to a gas station, you're probably going to burn most of that off driving home. And what's more, you needn't fill up until the gas level is RIGHT AT THE FUEL CAP. In fact, when I filled my Z, the level was usually 4 or 5 inches down from the cap. How much capacity is there in that 4 or 5 inches? I don't know, and I don't care enough to figure it out, but it makes the overflow problem even less likely.

 

I had gas stains on my car with an expansion tank. Turns out if you corner hard enough you'll find the limits of the filler neck and gas cap seals. Those stains in my case had nothing whatsoever to do with expansion.

[WEBEZEEed]

You guys can hash this out, but I recently reinstalled my expansion tank in my 73. I can say that the 2 years that it was out created no problems.

[Tony D]

"The Z has a 16 gal tank."

 

I'll drain my 73 Tank, and see just how accurate your statement is...

 

You're right John, Nissan put a phase separation tank in the car because they had a friend in the tank building business and wanted to keep him afloat. There's no expansion of fuel, and it will never overflow if it's given no place to go. Pressure will not rise in a sealed vessel, Boyles Law is a crock. There is no 10% by volume of expansion on gasoline, and filling to the rim of overboard vent in the JDM filler neck on a 40 degree morning will never have gasoline expansion so great as to cause overboard leakage from the tank...ever. It can't happen because physical laws don't exist and there is no good reason for the tank to be there in the first place.

 

The 64 tablespoons of expansion mentioned would never be enough to fill a 5mm line from the back of the car to the front and dump it in the crankcase, therefore the phase separation tank is a communist conspiracy foisted upon us by the bastards at Nissan to make our cars weigh more, raise the polar moment higher, and increase the costs of production to therefore decrease the gross profit of every vehicle.

 

How could I be so stupid as to not see this!I humbly implore your forgiveness at 'seeking the truth' in contravention of physical laws which I thought applied to all things on earth, but not to the Z Car or it's fuel system.

 

THIS NEVER HAPPENS PEOPLE! GAS DOES NOT EXPAND!

Edited October 27, 2010 by Tony D

[JMortensen]

I can recall putting 15.x gallons in my Z many times when it had the stock tank, and swear I got just a hair over 16 in mine once or twice. I think you can get 16 in pretty easily because the filler neck fills up a bit. The gauge also says 60L on it. You can also look up the specs online. This site says 15.9 http://www.carfolio.com/specifications/models/car/?car=36003. It would be nice if that were enough, but I expect a long dissertation about some stated but not actually used scientific principle TYPED MOSTLY IN CAPS that proves that 60L doesn't in fact equal roughly16 gallons and maybe some browbeating to go along with that.

 

If you look back, I don't disagree that the fuel expands, in fact I showed the mathematical coefficient of expansion. Due to finding the actual coefficient and it being vastly different from what you said, I think you're wrong about the amount the fuel really expands. You spout off "Boyle's Law" as if the mere mention of some scientific principle will end the argument. That is the "argument from authority" fallacy at work again. Show your work. I've shown mine.

 

If you look back at the classiczcars.com page again, you'll see that the 69 Z's didn't come with an expansion tank at all, because it's there to catch vapors and condense them and return them to the tank. It is a smog device. Expansion tank is apparently the wrong wording, the correct label would be "vapor tank". If you look at the position of the tank, if it were really intended to catch the expanding fuel, they sure decided to put it in the wrong spot! Looks like it doesn't have very much capacity before the fuel level rises to the height of gas cap. Most of the available space is above the fuel cap. As I said before, the gas cap and neck seals aren't tight enough to prevent splashing fuel from running out of my 70 with a metal expansion tank, stock hose routing and new gas cap and filler neck. I don't think it would hold up very well being under the fuel level, which I think it would clearly be if the expansion rate of the fuel was anywhere near 10%. It makes a lot of sense to put a vapor tank up high because it allows gravity to return the condensed vapors to the tank .

 

http://www.classiczcars.com/forums/attachment.php?attachmentid=9503&d=1128801645

 

In looking at the proposed changes again on classiczcars.com, I think there is one point on which we can agree. That is that routing the line from the top of the tank to the crankcase is a bad idea. I can't recall exactly where that hose went, I think it might end up on the driver's side fender and link into the vent tube off of the front of the block. If you park on a hill and the level of the tank is then higher than the level of the vent tube, and I'm correct about the routing, then you are right, gas is going to gravity feed into the crankcase. I would route that vent line back up to the filler neck with the others and plug it up front. With small bit of agreement in mind we can continue arguing about the expansion of fuel until the cows come home, but I did the math and checked several sources and I think you're wrong on that one.

 

I would however suggest that people don't fill up in Anchorage and then have a helicopter airlift their car to Death Valley. You might get some pretty severe leakage out of either system were that the case.

[WEBEZEEed]

1973 F.S.M. = 15 7\8 U.S. gallons.

[Tony D]

"because it's there to catch vapors and condense them and return them to the tank."

 

That's what 'phase separation' means John.

 

I already conceded you win. Gas expansion is not an issue, and the incontravertable evidence that the 69Z's didn't have one proves beyond a shadow of a doubt that they are unrequired, and indeed were only put there to keep a relative employed who happened to make expansion tanks.

 

15 7/8 is not 16 since pendantic adherence to form was what was being required and the forest was obscured by all the trees...

 

All I know is filling up on a winter morning and driving to work to let diurnal variation do it's thing on a black car will have fuel coming overboard out the filler neck vent (JDM fuel system) and puking fuel on the ground. This is not due to thermal expansion, it's due to bacterial breeding displacing the fuel. Or something else. Expansion is not the mechanisim causing the fuel to rise. That does not happen.

[Tony D]

Hmmm, true to my word, I've e checked and have run into a quandary... 16 gallons (15.87?)

 

That means 352 miles at 22mpg thereabouots right? But why did I only get 318 miles when the tank was sucked dry?(Box Springs Exit off the 60 in Moreno Valley) And when I put my 2.10 gallon can into it, and then drove till an indicated 328 miles to the same station where it was originally filled I was only able to put in 13.104 gallons up to the tippy-tippy top of the filler neck? No dents in the tank.

 

That's 15.204 gallons of fuel TOPS (discounting the probably 0.5 gallons consumed from point of empty to the station).

 

If that really was a 16 gallon tank...how is it that I'm a full gallon short of that capacity?

 

I think I shall have to posit how this could be... since you regularly filled up with 15+ gallons. And since the book says 15.9 (and 60L is 15.87 @ 3.78L/G)...

 

What could that capacity represent? Possibly total fuel system volume? Volume meant for expansion perhaps? I don't know...but explain to me on an undented tank sucked bone dry till the car stalled, with a known volume added...that barely adds up to 15 gallons? The tank retains 1 gallono in it when 'empty'?

 

Praytel Mr. Wizard, explain it. I should have gone 352 miles, but it stopped DEAD NUTS where I expected it to. Why? Where is that extra gallon you contend you fit in your magic tank?