Ballenxj
Formerly Southern Nevada, Idaho now
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^^Thanks for the info.^^
I guess the problem I found in the old days was the Thermoquad's housing always seemed to warp, rendering it useless. When I found one on a project car, I would replace it, and that usually cured the cars carb problems. It was common for mechanics back then to say they were not rebuild able.
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Griff in Fairbanks
AK
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StingrayL82 wrote:Yesterday I pulled the fuel tank. While the gas in it was rancid, the inside of the 51-gallon tank is pristine, no rust whatsoever. The sender still works, so it's getting a new filter sock and gasket. The tank is getting a good scrubbing and some fresh paint, along with new ethanol friendly hoses, as the old ones crumbled in my fingers.
I'm attaching some pics along with a question. If you look at the picture of the fuel tank, you'll see that the inlet is at the bottom. Now, I'm just a dumb linguist and not an engineer, but how can the fuel tank stay properly filled and not spew fuel back up the inlet hose?
![[image]](https://i.imgur.com/JOnUIWll.jpg)
I'm not sure if your fuel tank would pass an inspection. Sometime between the '70s and today, laws or regulations were put into effect outlawing fuel tanks with openings below the top of the tank. I had to abandon the original tanks in my '73 RM350 because they had drain bungs/plugs in the bottom of the tank. Where your fill is located makes it questionable from a legal perspective.
As for your fill-up question, there are two vent fittings on top of the tank. These will prevent air pressure from causing back flow into the gas fill hose. (I'm assuming your gas fill fixture -- where you insert the gas pump nozzle -- is higher than the top of the tank.)
One question -- does one or both of the vent hoses connect to the gas fill fixture? If not, I'd put small air filters on the vent hoses, to prevent grit from entering the tank.
You may experience some difficulties with automatic gas pump shut-off. The nozzles on modern gas pump use air pressure to detect when to shut off. Because you're dealing with an older tank, that doesn't conform to modern standards, the pump may shut off before the tank is approaching full. Likewise, the pump/nozzle may not detect full and cause gas to be spilled on the ground. (Gas stations can, and will, ban you for creating a HAZMAT incident.)
If you decide to replace the tank, one place to look is marine 'permanent' gas tanks. There are also places on the internet that sell custom tanks with in-tank fuel pumps. (In-tank fuel pumps are preferable because it's easier to push liquids rather than pull.)
1970 Explorer Class A on a 1969 Dodge M300 chassis with 318 cu. in. (split year)
1972 Executive Class A on a Dodge M375 chassis with 413 cu. in.
1973 Explorer Class A on a Dodge RM350 (R4) chassis with 318 engine & tranny from 1970 Explorer Class A
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Griff in Fairbanks
AK
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StingrayL82 - An option is to have the gas full inlet moved to the top of the tank.
This will be difficult because most welders won't go near a used gas tank, oil drum, etc., due to the risk of a fire or explosion. I'd look for the absolute best welder in your area. (If I was in your shoes, I'd be willing to travel 400 miles to find a reliable welder willing to do the job.)
I do both oxy-acetylene and wire feed welding. (I was taught 'no filler' welding and a friend was amazed when I showed it to him.) I wouldn't touch a used gas tank even though I know the procedure for doing so safely.
Even if the tank is complete emptied and purged, enough fumes remain to create a danger. In addition to completely draining and purging the tank, safe procedure involves filling the tank with water. Creating an airtight weld is very tricky due to the water drawing heat away from the weld. The tank also needs to be well vented because the water will boil, creating vapor pressure inside the tank.
If you choose this route, consider carefully where to place the new tank inlet. You will probably need to modify your coach to reroute the fill hose and possible move the exterior fill fixture.
You should also plan on resealing the tank with epoxy fuel tank sealant.
(I really hate thinking of something I should have added to a post after I hit the send button.)
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Leeann
Maryland
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Joined: 08/22/2006
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Actually, the best way to weld an old gas tank is to fill it with nitrogen. That's how my husband fixed his motorcycle tank years ago.
'73 Concord 20' Class A w/Dodge 440 - see profile for photo
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StingrayL82
Nampa, Idaho
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Griff in Fairbanks wrote:I'm not sure if your fuel tank would pass an inspection. Sometime between the '70s and today, laws or regulations were put into effect outlawing fuel tanks with openings below the top of the tank. I had to abandon the original tanks in my '73 RM350 because they had drain bungs/plugs in the bottom of the tank. Where your fill is located makes it questionable a legal perspective.
Idaho does not have an inspection program, so no worries there.
Griff in Fairbanks wrote: As for your fill-up question, there are two vent fittings on top of the tank. These will prevent air pressure from causing back flow into the gas fill hose. (I'm assuming your gas fill fixture -- where you insert the gas pump nozzle -- is higher than the top of the tank.)
Makes perfect sense, now that I read what you wrote.
Griff in Fairbanks wrote:One question -- does one or both of the vent hoses connect to the gas fill fixture? If not, I'd put small air filters on the vent hoses, to prevent grit from entering the tank.
Only one of those fixtures is for the vent. There is a hose that runs all the way up to the metal filler. No filter, but it's a great idea. The other fixture is the return. Monaco plugged the original return off at the sender...because of the extra capacity of the tank, it sits right up at the floor of the coach, so the fixtures have to bend 90° and the original return on the sender does not.
Griff in Fairbanks wrote: You may experience some difficulties with automatic gas pump shut-off. The nozzles on modern gas pump use air pressure to detect when to shut off. Because you're dealing with an older tank, that doesn't conform to modern standards, the pump may shut off before the tank is approaching full. Likewise, the pump/nozzle may not detect full and cause gas to be spilled on the ground. (Gas stations can, and will, ban you for creating a HAZMAT incident.)
My 1976 AMC/Jeep CJ-5 does the same thing. I have to be banned from any of the service stations here.
Griff in Fairbanks wrote:StingrayL82 - An option is to have the gas full inlet moved to the top of the tank.
This will be difficult because most welders won't go near a used gas tank, oil drum, etc., due to the risk of a fire or explosion. I'd look for the absolute best welder in your area. (If I was in your shoes, I'd be willing to travel 400 miles to find a reliable welder willing to do the job.)
My father-in-law is a retired master welder, did all of the chassis for Kit Travel Trailers here in Idaho for 30 years. He's done plenty of fuel tanks for friends and family with no problems.
Griff in Fairbanks wrote: Even if the tank is complete emptied and purged, enough fumes remain to create a danger. In addition to completely draining and purging the tank, safe procedure involves filling the tank with water. Creating an airtight weld is very tricky due to the water drawing heat away from the weld. The tank also needs to be well vented because the water will boil, creating vapor pressure inside the tank.
I have had to weld on fuel tanks before and have always purged them with CO2 and have never had one single issue. I also insert an inert gas, when welding, to promote a better weld, especially with TIG.
Griff in Fairbanks wrote: You should also plan on resealing the tank with epoxy fuel tank sealant.
The inside of this tank is immaculate, there is no rust whatsoever in it. The zinc is still visible, so no need to reseal it.
Griff in Fairbanks wrote:(I really hate thinking of something I should have added to a post after I hit the send button.)
I know what you mean. I do it all the time. I really appreciate the responses. Forums are great for learning new things, as well as re-learning things forgotten.
Fred
Retired Army Guy
2005 Monaco LaPalma 37PST
Workhorse W24 chassis
8.1L Vortec
Allison 2100 MH
Onyx Color Scheme
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Ballenxj
Formerly Southern Nevada, Idaho now
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StingrayL82, it would seem you have all your bases covered.
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StingrayL82
Nampa, Idaho
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Ballenxj wrote:^^Thanks for the info.^^
I guess the problem I found in the old days was the Thermoquad's housing always seemed to warp, rendering it useless. When I found one on a project car, I would replace it, and that usually cured the cars carb problems. It was common for mechanics back then to say they were not rebuild able.
Over-torquing the screws and heat are the ThermoQuad's Achilles heel. What I really love about the ThermoQuad, as well as the Quadrajet, is when you hit that go pedal and the secondaries kick in, and you hear that roar of the air being forced down into the intake.
Ballenxj wrote:StingrayL82, it would seem you have all your bases covered.
I try, believe me I try. In the end, though, it always seems like I've forgotten that ONE thing that comes back to bite me in the rear end.
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eyeteeth
SW Michigan
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Joined: 09/26/2006
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The other nice thing about thermoquads... is you can find them on ebay cheap if you need parts... say... to replace a warped bowl.
The hard part is finding someone old school enough who knows how to really tweak and tune them properly.
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StingrayL82
Nampa, Idaho
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eyeteeth wrote:The other nice thing about thermoquads... is you can find them on ebay cheap if you need parts... say... to replace a warped bowl.
The hard part is finding someone old school enough who knows how to really tweak and tune them properly.
If the bowl isn’t too bad, take a piece of glass, put sand paper on it and rub the bowl lightly on it, in circular motions. 9 times out of 10 it’ll fix the problem, unless it’s too far gone.
The old school part....****, I must be getting old....I grew up around the ThermoQuad and Quadrajet, so tuning them is pretty easy for me. It’s finding good needles and jets that’s starting to be the issue with the ThermoQuad
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eyeteeth
SW Michigan
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It was too far gone. I got it flat, but the sides were also bowed out. Became obvious when it was mostly flat.
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