Gas tank full of rust.

gearjammer · Post by **gearjammer** » Mon Dec 03, 2012 3:26 pm

Hey Guys, So the new old 71 I just got has a gas tank full of rust. Why do I think they don't make a replacement for this? What is the best way to go about fixing this thing? Thanks

66patrick · Post by **66patrick** » Mon Dec 03, 2012 5:51 pm

Welcome to the rusty gas tank club. Not a phenomenon unique to Swepties, this is a problem with today's fuels and their abilities to attract moisture, because of the ethanol content. No one reproduces tanks for these, but there are alternative tanks you can use, like a tank from a Ramcharger, an early Blazer or Suburban (the tank doesn't care what it's in!), or others. Which, if your goal is to eliminate the in-cab tank in the process...!

You can remove and take to your local radiator shop, where they will boil it out, then leak test it. Or you can load it with a bunch of small pebbles and rotate it for some time to bust the rust loose. It's gonna take some work.

Enjoy!

gearjammer · Post by **gearjammer** » Mon Dec 03, 2012 7:05 pm

I'd like to keep the tank behind the seat...original tank is the worst Z've ever seen on the inside. My buddy sez he cuts a door in his tanks and has them sanblasted then welds mem back up.I'm afraid this one will turn to dust....How about using a chevy [mid sixties] tank...do they remotely fit? they repop these...

Post by **wally426ci** » Mon Dec 03, 2012 7:06 pm

I used heavy duty cleaner and stuck a chain in it and banged it around for a long time. Keep washing it out.

PwrWgnDrvr · Post by **PwrWgnDrvr** » Mon Dec 03, 2012 8:18 pm

The rust only comes from one place - the metal of the tank. Every layer of rust that comes off makes the tank wall thinner. Only a matter of time til the pinholes develop. The only options are replacement or having the tank lined. The 70/71 tank is larger than earlier yrs, but any sweptline tank can be made to fit by drilling new bolt holes in the flange.

66patrick · Post by **66patrick** » Tue Dec 04, 2012 9:41 am

When I get around to replacing the tank in the '68, I'm going to use a 34-gallon Ramcharger tank. Perfect fit in the frame rails (same width in back in a Ramcharger and a Swepty), plus I can use the sending unit and all from the RC. No in-cab smell of fuel. If you really want range, use the stock AND the RC tanks, which would give you about 51 gallons.

gearjammer · Post by **gearjammer** » Wed Dec 05, 2012 2:50 pm

Well here is an update.

I bought a readily availible 70-71 Chevy c-10 tank [behind the seat] $150 on ebay..You have to unsolder the Fuel cap bung...and use your gennie dodge.

You have to cut off the excess top flange on the new tank and on mine I had to beat in [up] the very bottom of the new tank about 1/4 of an inch. ..Then the tank just slide into position very well. Then you have to bend [re-angle] the bottom flange of the new tank to the contour of the Dodge cab..drill a few holes and bolt it in

You have to slide in the Dodge gas filler neck , [slight adjustment to the hole in the tank] I was able to bolt the neck back to the door jamb with the original everything with no major problem. You need to get the Chevy sending unit [the parts place Chicago Ill..] $30 I have yer to receive the sender..I have no idea how the Chevy sender will work in the Dodge. Sender in my tank was shot. I'll give an update on the sender issue as I complete it.

So far this is where i am. You can't use the Dodge grommet to slide the filler neck into the tank. I will be using probably two types of gas tank repair kits to seal the old neck to the new tank. One is the two part putty epoxy...I'll jamb that around the outside and then after it hardens I'll use the two part epoxy [fluid] to pour over the seam as a second seal.

66patrick · Post by **66patrick** » Thu Dec 06, 2012 1:44 pm

The GM and Mopar sending units have a different resistance, IIRC, so I do not believe your sending unit will work with your factory gas gauge.

rockingkay · Post by **rockingkay** » Fri Dec 07, 2012 6:53 am

The Chevy would have a 0-90 restaince. What would the Dodge be? I thought they were all the same in this time period.

gearjammer · Post by **gearjammer** » Fri Dec 07, 2012 2:00 pm

I did a super quick search...

the Chebbie should be 90 empty and 0 full

Our dodge should be 73 empty and 10 full

So if that is true...Full should be close and maybe 1/4 tank would show empty...

I have the chevy on order, I'm going to check it before I put it in.

Sorry to say the Dodge unit was shot. No way to check that.

PwrWgnDrvr · Post by **PwrWgnDrvr** » Fri Dec 07, 2012 7:42 pm

Less than 10 full means the gauge will be conducting a higher amperage. More amps = more heat = burned out gauge.

rockingkay · Post by **rockingkay** » Fri Dec 07, 2012 8:14 pm

resistanse is ohms not amps. The float works by resisting the flow of ground to the gauge. I dont know if 10 ohm less resistants would really burn up the gauge, but it would say it was full when it was not, and you would be walking with the gauge saying you have gas. So ether way it wouldnt be cool.

PwrWgnDrvr · Post by **PwrWgnDrvr** » Sat Dec 08, 2012 1:02 am

rockingkay wrote:resistanse is ohms not amps. The float works by resisting the flow of ground to the gauge. I dont know if 10 ohm less resistants would really burn up the gauge, but it would say it was full when it was not, and you would be walking with the gauge saying you have gas. So ether way it wouldnt be cool.

Ohms law dude
I=E/R
Volts divided by ohms = amps
Less ohms means more amps
more amps means more heat
more heat burns stuff out/up

fyi:
- it is spelled resistance, not resistanse, nor resistants
- the float works by displacing fluid (the fuel) that has a higher specific gravity than the float
- "ground" does not flow
- you are correct when you said "I dont know..."
- it is spelled either, not ether
- you are also correct when you said "it wouldnt be cool" [when the gauge burns up]....(it would be hot!)
- the 0-90 sender with a Dodge gauge would never show the tank having gas when it didn't.
(when the sender reaches 73 ohms at aprox 1/4 tank, the gauge will read empty, but there is still 1/4 tank of fuel.)

mikeys_toy · Post by **mikeys_toy** » Sat Dec 08, 2012 4:24 am

moot point anyway as the gm sender would make the guage read backwards
0 ohms = empty gm
90 ohms = full

73 ohms = empty mopar
10 ohms = full

At 0 ohms the guage would peg and burn out after a while.

rockingkay · Post by **rockingkay** » Sat Dec 08, 2012 5:01 am

Well I just stepped all in the stink. I didnt know that was a spelling test. I do remember seeing the amp eqation in the paper for the ohm meter, sorry about that. and power does flow. It is a current. Which is probly not spelled right, so I hope it does make you mad.And I stand by what I said. yes the float is floating on the gas but as it drops its contacted is draging acrossed a wrap of copper wire. The closer it is to the by screw on top of the float,the less resistance,the more warps of wire the power has to flow through, the more resistance. I still dont think a differants of 10 ohms would burn the gauge up ,as it wouldnt get to this points unless the tank was full or empty,which ever way was to the end of the wire wrap. But none of this m atters because what it comes down to is the gauge want read right. I cant find spell check on here, I am sure someone will want corect my spell, you might want to check if all the period are in the right place being it sound like you are on yours. Please note the lite blue wire on the right is the sending unit. See the to ground symbol on it. Ok I know it is 68 but they all would be the same. This and a lot of wire is were my truck started no wireing in the truck. It all works.

PwrWgnDrvr · Post by **PwrWgnDrvr** » Sat Dec 08, 2012 9:19 am

mikeys_toy wrote:moot point anyway as the gm sender would make the guage read backwards
0 ohms = empty gm
90 ohms = full

gearjammer wrote: the Chebbie should be
90 empty
and 0 full

Which one is correct?

WD · Post by WD » Sat Dec 08, 2012 10:31 am

Such a minor problem with such a simple solution. Buy a stand alone fuel gauge in the right resistance. $10 and 2 screw holes to drill for the mounting bracket. Done.

Unless you are going for a perfectly stock looking dash. Then you send your gauge off to one of the rebuilder shops listed in Street Rod magazine and have a new set of working bits put behind your gauge face.

gearjammer · Post by **gearjammer** » Sat Dec 08, 2012 1:39 pm

The Chevy unit came in today and it reads 0 empty and 95 full. {aftermarket reproduction]

It would suck if the dodge sender is opposite.. Gauge reads empty unhooked...does a chevy read full unhooked?

I tried grounding the factory wire to the dash and I got no change...I'll futz around with it more on Monday.

I'm guessing I'm going to end up buying ANOTHER sender..for maybe a Barracuda and remove the sender and graph it onto the chevy fuel unit. But first I have to see why the gauge seems dead regardless..... I'll get it figured out...its only money, right?

jkindt · Post by **jkindt** » Sat Dec 08, 2012 7:57 pm

mikeys_toy wrote: 73 ohms = empty
10 ohms = full

This is correct, I measured mine.

WD · Post by WD » Sat Dec 08, 2012 8:02 pm

There is a tiny ballast resistor looking unit in the fuel gauge. They are notorious in 40s-70s Mopars for going up in smoke. Open the gauge casing, odds are the resistor is burned out. Looks like a light bulb filament.

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