1977 King Cab Fuel Tank Issue

[wolfxdog]

Afternoon y’all,

I have a automatic 1977 620 king cab deluxe and have been slowly working on it since I got it three years ago and Im having issues with power etc and learned that from the previous owner the fuel tank went to hell sitting in a parking lot for years.

I have a few options I’m considering.

 

1. Have the tank taken off an refurbished and then put back on which will be about 1k

 

2.Buy an expensive new tank from Asia.

 

3. Maybe build my own beer keg fuel tank and mount it in the bed.

Thoughts?

 

This is my 2nd post but I’ve been following this site, checking topics and reading and using it for a lot of help and questions I’ve had.

super thankful for this community.

 

I’m based in North East Portland if any of y’all are my neighbors.

[datzenmike]

You don't say if leaking or maybe just rusty. What's wrong with it? Maybe just buy a fre fuel filters and drive it till it collects all the rust.

 

Through '77 the tanks mounted to the bed, '78 and '79 they mounted to the frame. They are so similar that a later could be made to fit an earlier one. A wrecking yard tank is an option.

 

 

$!,000 to fix old tank????? They saw you coming. Drain and remove. Take the float gauge sender out. Put a shovel full of clean driveway gravel in and shake and roll it about to loosen and remove any rust. Sit and rock it over side to side for half an hour till thoroughly clean. I lost track of how much this has cost so far. Oh yeah, nothing. Empty out and rinse. Repeat if necessary. Let sit in sun for the afternoon to dry it out or indoors over the heater. Still cost nothing.

 

Now... are there pin holes or leaks??? If no put back together.  Cost only your time.

 

Pin holes or leaks around the seam? There are dozens of gas tank sealer kits on the market, pick a good one not the cheapest. Not necessarily this one. Follow directions, pour in and rotate tank to cover the inside and let dry. Preparation is everything.

 

Check and make sure you get enough for a car gas tank. You might need two. So far, well under $100

[datzenmike]

 

Definitely no beer keg gas tank.

[wolfxdog]

32 minutes ago, datzenmike said:

You don't say if leaking or maybe just rusty. What's wrong with it? Maybe just buy a fre fuel filters and drive it till it collects all the rust.

 

Through '77 the tanks mounted to the bed, '78 and '79 they mounted to the frame. They are so similar that a later could be made to fit an earlier one. A wrecking yard tank is an option.

 

 

$!,000 to fix old tank????? They saw you coming. Drain and remove. Take the float gauge sender out. Put a shovel full of clean driveway gravel in and shake and roll it about to loosen and remove any rust. Sit and rock it over side to side for half an hour till thoroughly clean. I lost track of how much this has cost so far. Oh yeah, nothing. Empty out and rinse. Repeat if necessary. Let sit in sun for the afternoon to dry it out or indoors over the heater. Still cost nothing.

 

Now... are there pin holes or leaks??? If no put back together.  Cost only your time.

 

Pin holes or leaks around the seam? There are dozens of gas tank sealer kits on the market, pick a good one not the cheapest. Not necessarily this one. Follow directions, pour in and rotate tank to cover the inside and let dry. Preparation is everything.

 

Check and make sure you get enough for a car gas tank. You might need two. So far, well under $100

Thank you so much mike! So glad I asked!

 

it’s a rust issue, I’ve been popping the filters out for awhile because that was doing the trick and the trick would run but have issues every now and then with losing power/not getting enough fuel.

Then recently it just started dying/losing power and rolling to stop like I’ve run out of gas(didn’t) so I brought to a shop I’ve used for years with my old van and that’s when they quoted and told me about the tank.

 

I don’t think there’s any leaks but I’ll find out because on one of my days off here I’m definitely following your advice and getting under the truck.

 

this is so helpful!

 

taking the tank off should be pretty straight forward yeah?

 

Total newb here to basic mechanics but learning.

[datzenmike]

Should be a drain bung in the bottom. Drive till empty if possible. Drain completely in an open airy place outdoors. Have a fan blowing from a distance so fumes can't collect. This was in my 710 gas tank...

 

 

Tank has wire for the gauge, a fuel line to the pump and a return line, there should be a vent line to the charcoal canister by the rad to trap fumes and the fill hose.  The bolts holding it in will be rusty and likely to snap off, drill them out after the tank is removed and just replace with nuts and bolts. It's easy to forget that gas vapors will easily catch fire and a closed tank can explode so have the cap off. When out fill with water to the top, what little gas there is, is lighter and floats to the top and will spill out.

 

 

[EDM620]

3 hours ago, datzenmike said:

Through '77 the tanks mounted to the bed, '78 and '79 they mounted to the frame

This is a very easy swap and you'll gain in capacity as well. The KC has 2 available tanks, the 4x4 one adds a little depth  therefore a bit more volume to boot. I swapped my original 620 bed-mounted tank for a 720KC 4x4 tank - just add bolts (note I also swapped frames so the mounting brackets were there).

 

Worst case, I have my original 620 tank available, a good number of miles North of you, but it is solid.

[EDM620]

The 620 KC tank is like Datzenmike noted, bolted to the underside of the box on the 2 crossmembers. See this pic.

The 720 tank is frame mounted to these 2 highlighted brackets, and is shaped to clear the back part of the cab.

The tank is Spectra NS11B - if you can source it in the US (made in Canada).

 

These are the parts involved (720 model).

[EDM620]

I just had a quick look on RockAuto, they list fuel tanks from 1983 up 720. You have some options now.

[wolfxdog]

Edm620 so I could swap and throw a 1983 720 gas tank on mine without much work beyond some bolts?

or would I actually need to do some welding and metalwork?

[datzenmike]

The '78-'79 620 is the same as the 720 for gas tank mounting.

 

If you have a regular cab then a 720 regular cab tank should fit close enough. Reg cab 2wd and 4wd tanks were the same through '82 and are 50 liter 13.2 US gal. Your '77 is 45 liters or 11.8 US gal.  720 KC tanks have the notch for cab clearance.

 

Still might be easier to coat your old tank.

[EDM620]

On 1/7/2023 at 8:13 AM, datzenmike said:

Still might be easier to coat your old tank

That is certainly true, however the option of replacing the tank (and gaining capacity) is a good second choice if the reseal isn't effective. Mounting up the tank is the key to swapping.

 

I had a Cherokee diesel that the tank had hundreds of pin holes, the result of muck being trapped between the skid plate and tank. As a very temporary fix, I rubbed a bar of soap all over the bottom - the bar soap reacts with fuel and will plug the holes, but will also wash off eventually - an effective temporary patch though.

[EDM620]

On 1/6/2023 at 11:36 PM, wolfxdog said:

without much work beyond some bolts?

or would I actually need to do some welding and metalwork

That totally depends on being able to mount the tank. If factory mounts exist, then it's just bolts, otherwise you need to fabricate the mounts.

[datzenmike]

The front sides of the '73-'77 tanks bolt to vertical mounts to the bottom of the bed. The very rear across the back of the tank also have a vertical mount to the bed. So 2 bolt holes at front sides and 2 holes across the rear.

 

The front of the '78-'79 tank bolts directly to a horizontal strut on the frame. The rear of the '78-'79 tank bolts to a vertical mount to a strut on the frame. So 4? bolt holes across the front and 2 across rear of the tank.

[RyanC]

I pulled my 620 tank as the pickup was blocked completely hard!!

 

Removed the sender washed with water then got a chicken stick and candle for any extra fumes, no explosion occured 😉

 

I had a piece welded to the underside and fitted a pickup to this so now it has a tiny 2inch x 2 inxh resevoir in the bottom and don't use the original pickup.  

When washing I threw an old chain in the tank and sloshed it all over to removed scale etc and most came out.  If it wasnt for the gunked up pickup would have been easier.

[bilzbobaggins]

20 minutes ago, RyanC said:

I pulled my 620 tank as the pickup was blocked completely hard!!

 

Removed the sender washed with water then got a chicken stick and candle for any extra fumes, no explosion occured 😉

 

I had a piece welded to the underside and fitted a pickup to this so now it has a tiny 2inch x 2 inxh resevoir in the bottom and don't use the original pickup.  

When washing I threw an old chain in the tank and sloshed it all over to removed scale etc and most came out.  If it wasnt for the gunked up pickup would have been easier.

Whats a chicken stick and a candle?  Never heard that one

[RyanC]

🤣🤣

 

Just aussie slang for a long stick which I tied a candle to rather than getting up close and personal with the fuel tank and a flame 😁

[datzenmike]

What was the candle for? I've worked on a gas tank before and just filled with water leaving a bubble at the top where I was soldering or welding. 

[KELMO]

Excess fumes. However, I think I would prefer your method.