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View Full Version : Mark VIII Gas Tank w/Dual Pumps?



DrFishbone
11-14-2017, 10:33 AM
I know this has been thought of before, but I'm not aware of anyone (here at least) that has went through with it...

I need more fuel to continue running E85 and would like to explore the dual in-tank pump option first....from what I can tell, it's doable with a T-Bird tank. David Neibert has it done on his car, and I'm sure a few others.

I'm pondering using a late model Mark VIII tank (97/98)...it looks like they use the fuel pick-up bucket like some other late 90's, 2000's Ford cars. It also appears that the sending unit drops the pump / hanger assembly more "straight-down" than the T-bird setup. I'm wondering if this would facilitate arranging dual pumps more so than the T-bird tank. I'm aware there are minor differences in the exhaust path....I don't really care about that right now. ;) There have been other members that have verified that it will bolt it in, so I think that is out of the way.

67996

Also wondering what weight difference there would be between the Mark VIII steel tank and the 92+ T-Bird plastic tank...I doubt it's much - the plastic tank is pretty heavy. A few Google images came up with a factory, gasketed fuel pump access door too...might try to make that work in the process, if I go this way.

I'll be replacing the fuel line fittings out of the hat, and I think I should be able to reuse the sending unit without issue this way.

Anybody care to share their experience and/or research?

BLOWN38
11-14-2017, 10:46 AM
All you. Git er dun!:cool:

DrFishbone
11-14-2017, 11:10 AM
Also wondering if the dual-pump Cobra fuel hat assembly would fit....I'd probably want to redo it in AN fittings anyway though.

There's also the materials compatibility thing though....not sure there...finding mixed results on materials compatibility charts. I'm not too concerned on that point....the stock fuel hat / tubing is plated steel.

Kurt K
11-14-2017, 11:21 AM
I'm following because I need a fix for my leaking hat gasket (replaced twice: still leaks, so I think it is the tank). Is the Mark VIII tank essentially the same shape (driveshaft tunnel and exhaust channel)? If nearly the same, I'm hoping my exhaust would not need to be modified.

DrFishbone
11-14-2017, 11:57 AM
I'm following because I need a fix for my leaking hat gasket (replaced twice: still leaks, so I think it is the tank). Is the Mark VIII tank essentially the same shape (driveshaft tunnel and exhaust channel)? If nearly the same, I'm hoping my exhaust would not need to be modified.

Did you replace the ring too, Kurt? Also, I've had the solder joint break on one of the lines into the hat, causing a leak.

Swapping a tank would be more fun though. ;) From what I've read, 93-96 had a plastic tank - possibly identical to the Thunderbirds/Cougars....97/98 had the steel tank with (for sure) different sending unit / hat assembly.

BLOWN38
11-14-2017, 01:35 PM
I'm following because I need a fix for my leaking hat gasket (replaced twice: still leaks, so I think it is the tank). Is the Mark VIII tank essentially the same shape (driveshaft tunnel and exhaust channel)? If nearly the same, I'm hoping my exhaust would not need to be modified.

Did you replace the metal ring at some point? The Dorman ring does not have the bends in it to put tension on the oring when it is locked down. I replaced mine with a stock ring and all is well. You could probably put the bends in the Dorman ring if you had to. I can try to get some pics.

Kurt K
11-14-2017, 04:16 PM
Did you replace the metal ring at some point? The Dorman ring does not have the bends in it to put tension on the oring when it is locked down. I replaced mine with a stock ring and all is well. You could probably put the bends in the Dorman ring if you had to. I can try to get some pics.Stock ring, new gasket (twice).

DrFishbone
11-14-2017, 04:37 PM
Did you replace the metal ring at some point? The Dorman ring does not have the bends in it to put tension on the oring when it is locked down. I replaced mine with a stock ring and all is well. You could probably put the bends in the Dorman ring if you had to. I can try to get some pics.

I think I remember having to add a little more bite on mine...it was probably a Dorman replacement

Jacob_Royer
11-14-2017, 05:46 PM
Kurt I had a similar problem had to re/solder the return line to the hat it was only partially sealed.

DrFishbone
02-12-2018, 01:21 PM
Well, finally got to the yard to have a closer look at the steel MK8 tanks. As they warn, they really tear-into the tanks in order to drain the fuel. :( The one tank they had has a 1.5í cut from front to back, and a 2nd cut thatís about 6Ē long right by the sending/pickup. So, itís pretty much ruined.
However, I do think a dual-pump setup, re-using the factory sending unit would be much easier to do a clean, solid and safe modifcation for our SCís. The hat is stainless, large, nice and flat Ė perfect for adding AN fittings and a new electrical bulkhead to. The unit drops straight down into the tank, so even if the assembly is a little larger, fitting it in should be doable.

I didnít weight each of them, but I think the steel tank is a few pounds lighter tooÖ.maybe 5lbs or so. I assume this is mainly because the large shield isnít needed on the steel tank. There are a few gadgets that the MK8 tank has that the SC tanks donít Ė I assume a ventilation system and probably a pressure sensor too.

I think Iíll spend a little bit of time looking for a cheap tank like this that doesnít need repaired. Iím not completely opposed to a fuel cellÖmaybe thatís weíre Iíll end up. I thought this was at least worth exploring some more though.

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DrFishbone
02-12-2018, 01:23 PM
I think the commercially-available Mustang dual-pump hanger assemblies might drop right into this, if you want to spend a few bucks. If not, I'm sure a way to add a second pump and maintaining the sending unit wouldn't be too hard. The receiver...or baffle...in the tank would probably have to be modified a little too in order to make room for another pickup screen.

racecougar
02-14-2018, 10:05 PM
Well, finally got to the yard to have a closer look at the steel MK8 tanks. As they warn, they really tear-into the tanks in order to drain the fuel. :( The one tank they had has a 1.5í cut from front to back, and a 2nd cut thatís about 6Ē long right by the sending/pickup. So, itís pretty much ruined.

The rule at the local shredder is that the fuel tank has to have a hole big enough to fit a basketball through for them to accept the car.

What size pumps are you looking to run?

DrFishbone
02-15-2018, 12:36 PM
The rule at the local shredder is that the fuel tank has to have a hole big enough to fit a basketball through for them to accept the car.

What size pumps are you looking to run?

I'm waffling between two 255's and two 340's. I have a 340 right now...might have my old 255 somewhere too though. I guess there's nothing technically wrong with using one of each either. :confused:

I haven't seen where the Walbro 255HP's are advertised as being suitable for E85....just feedback on other car forums where people have been using them for X years. Of course, who's going to say that and then admit they were wrong when they have a problem? ...not many. :rolleyes:

Depending on whether or not a good steel tank shows up, I may just do a fuel cell, then who knows what I'll do for a pump / pumps.

Right now, I'm thinking of reusing my existing fuel line (8AN...not dual feeding the rails yet) and doing dual 8AN lines, one to each rail, then a new FPR and 6AN return to tank. Way more than I need right now, of course....just don't want to have to re-do it again in a few years.

DrFishbone
07-03-2018, 12:20 PM
Looks like I may have located a tank without holes that I can easily pick up.....$50 already removed. :D

That being said, I guess I'll be giving this dual-pump idea a shot.

I'm thinking I'll run one normally with the second pump on a Hobbs switch, but have the wiring such that I can switch between the two easily (in case of a failure). Still run dual lines, one to each rail, but arrange the lines such that there is a crossover between the two.

Probably will look at picking it up sometime in the next few weeks, but won't get to it until later, most likely.

J dot Miller
07-04-2018, 01:06 PM
Following this thread

racecougar
07-06-2018, 07:08 PM
Planning to install check valves?

DrFishbone
07-09-2018, 12:37 PM
Planning to install check valves?

I wasn't, but can if needed.

Don't the pumps have a check valve (or at least function as one when not running)? Which is why you can hold FP after the pump stops.

racecougar
07-09-2018, 12:49 PM
It depends on the pump. Some of the larger turbine-style pumps don't have an internal check valve.

DrFishbone
07-10-2018, 12:56 PM
Looks like I may need at least one check valve if doing dual Aeromotive pumps - thanks Rod.

That also puts my mind at ease after seeing the fuel pressure gauge at the rail showing the pressure bleeding off somewhere. ;)

J dot Miller
07-12-2018, 07:16 PM
If it was me I would have one on each pump. For example, if one pump fails it could pump back into the tank instead of the fuel rails. Liquid takes the path of least resistance. :eek:

ScrapSC
07-19-2018, 11:14 AM
I modified my hanger and installed the 450 pump for E85 that is out now.... Used a line from "radium" to go from pump to the bottom of the hat.... From there I have -8 split to each side of the rail and back to tank with -6. All ptfe line that is coated.

DrFishbone
07-23-2018, 12:56 PM
I modified my hanger and installed the 450 pump for E85 that is out now.... Used a line from "radium" to go from pump to the bottom of the hat.... From there I have -8 split to each side of the rail and back to tank with -6. All ptfe line that is coated.

Is that going to be enough fuel flow for you at 60psi+?