Prado 120 sub tank in a GX470 - has anyone done it? Well I’m gonna try! (1 Viewer)

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FYI lots of cars use a siphon powered by the flow from the fuel pump to transfer fuel between tanks so I'm sure there are ways around sourcing some of the lines if thats what you're concerned with. My 2GS has a saddle tank and uses a siphon to move fuel from one side to the other where the fuel pump is.
 
The parts that I consider essential are the tank itself and the items that go in the 4 openings in the tank:
-the fuel feed and vent return
-the vent to evap/ charcoal canister
-the fuel level sender
-on the side the fuel filler and filler vent

These would be the most difficult to work around or build from scratch, at some point it would just make more sense to use the aftermarket LRA tank.

Although I plan to use the Prado filler neck and fuel pump those could be worked around. You only need the tee fitting for the filler and that could be cut into the GX filler with sections of rubber hose and clamps. For the fuel pump you could just install a low pressure electric transfer pump on a switch. This is how the LRA kit addresses these two items. I like the simplicity and automatic function of the OEM setup so I plan on using it instead. Of course my plan may change once I have the parts in hand and discover any unknown complications. I have been following @grinchy thread where he is installing the sub tank in a 200 and working through the configuration differences of the US vs non US fuel and evap systems.


It’s very likely there will be a few issues I didn’t anticipate.
 
The first parts order has shipped from Japan. I have also placed the second order from UAE which the two together will have the filler neck as well as all the components of the sub tank (tank, mounting, filler piece, fuel and vent pieces, sender, basically everything to make the air tight tank assembly). I will still need to place an additional order for the fuel pump and the hoses. I wanted to get a chance to measure all of the hose barbs on the tank to see what I actually need OEM hoses for, and also see the size of the filler and if it is the same size as stock. @grinchy found out that the 200 series sub tank filler is 1/4” larger than the US spec filler so had a bit of a challenge attaching the rubber filler hose to it. The 120 may be similar...

I also ordered a new fuel pump male plug so I can build a pigtail to tie in the sub tank sender via switch to the fuel gauge. I am thinking I will run 6 conductor trailer wire to the switch which will allow for main tank sender to switch, sub tank sender to switch, and switch back to where the main tank sender originally tied into the wire to the fuel gauge. The part number for the plug is 90980-11077 a pic of it can be found here:


Does anyone know how to determine what size sumitomo terminals and seals it should take? Also does anyone know how to find a Toyota connector based on a picture of it? I need to find the same connector for the sub tank sender which should be a two terminal connector, but I won’t know what it looks like until the sender gets here.
 
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Nice project! I'm following this..

How does the Prado deal with the extra weight of a full sub tank suspension wise?

I have the Prado rear springs on my GX through the Metal Tech conversion kit, they seem almost too weak/soft and bottom out frequently when I just have 3rd row seating installed.
 
Nice project! I'm following this..

How does the Prado deal with the extra weight of a full sub tank suspension wise?

I have the Prado rear springs on my GX through the Metal Tech conversion kit, they seem almost too weak/soft and bottom out frequently when I just have 3rd row seating installed.

The capacity of just the subtank is around 24 gallons and gasoline is a bit lighter than water at 6.3 lb/ gallon, so the gas in the tank is about 150lb plus the weight of the components themselves, maybe 100 lb with a beefy skid plate. That's about the same as having a hefty friend or a couple of teenage kids in the backseat. I am running OME 895 coils IIRC so if the weight is too much I can always swap in a heavier spring. I'm also planning on adding a tire carrier and some armor.

Excellent thread! I’ve wondered about this since seeing a Prado hatch mounted spare.

My spare (255/80r17) no longer fits under the vehicle without hitting the panhard, so a tire carrier is on the build list. And I may go bigger in the future.
 
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Forgive me if this has been discussed before as I quickly scrubbed through this thread. Regarding the electronics and plumbing aspect of this project, might I suggest y'all look at how the 80 series subtank works? I have the factory subtank that uses a simple transfer ECU by George aka TaskLED that automates the fuel transfer from the sub to the main tank beautifully.. As far as the plumbing, an aftermarket low pressure, high volume fuel pump mounted to the frame rail transfers the fuel from the sub to the main using the main vent pipe. More details here . All you need from the sub tank is the "empty" signal so that the ECU knows when to stop transferring fuel. The empty discrete signal is usually paired with the analog level signal, at least that's how it is in my sub tank.

I don't have a need for a level indication so I opted to not have one but the sub tank does come with an analog level sending unit that can easily be hooked up. I thought about hooking it up to the main tank level gauge using a toggle switch as I think both sending units have the same resistance scale but I never followed through.

The dual filler neck is a work of art for the 80/100 series and I hope the Prado platform has something similar.

Good luck!
 
Forgive me if this has been discussed before as I quickly scrubbed through this thread. Regarding the electronics and plumbing aspect of this project, might I suggest y'all look at how the 80 series subtank works? I have the factory subtank that uses a simple transfer ECU by George aka TaskLED that automates the fuel transfer from the sub to the main tank beautifully.. As far as the plumbing, an aftermarket low pressure, high volume fuel pump mounted to the frame rail transfers the fuel from the sub to the main using the main vent pipe. More details here . All you need from the sub tank is the "empty" signal so that the ECU knows when to stop transferring fuel. The empty discrete signal is usually paired with the analog level signal, at least that's how it is in my sub tank.

I don't have a need for a level indication so I opted to not have one but the sub tank does come with an analog level sending unit that can easily be hooked up. I thought about hooking it up to the main tank level gauge using a toggle switch as I think both sending units have the same resistance scale but I never followed through.

The dual filler neck is a work of art for the 80/100 series and I hope the Prado platform has something similar.

Good luck!

The 120 and 200 subtank systems are more simple than the 80 system, I know the 80 filler has to be toggled between which tank you are filling and the 120 just has a Tee in the filler and fills both tanks at the same time. The pumping system is also more simple, the 80 has a pump for the subtank (that either fills the main or supplies the engine I am not sure) but the 120 just has a syphon built into the main tank fuel pump. It siphons gas from the subtank and keeps the main tank full until the subtank is depleted. The only electrical in the entire system is the sender in the subtank and its a 2 wire that tells the level of the tank. I am planning on using a toggle to switch between which sender the fuel gauge reads similar to what you are describing.

I like that the 120 system doesn't use a separate pump and is completely automatic, its one less thing to keep track of.
 
First parts order from Japan has arrived. The critical components are the filler fitting of the sub tank, and the vent to evap fitting. The cushions go on top of the tank between the tank and tub, these aren’t really critical they could be made out of rubber gasket stock.

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This is awesome.
 
Is this concept substantially different from what Long Range Automotive sells? Are you just trying to cut cost down?

Not substantially different in concept but some small differences in execution. The biggest difference is that the LRA pumps gas from the sub to the main by toggling a switch where the OEM setup is automatic. Aside from that LRA is notched on top so you don't have to relocate the charcoal canister, I don't know if their setup is CA legal but I am pretty sure mine will not be - since I am moving the charcoal canister the evap system is considered modified.

Yes it will cost less and will be OEM instead of aftermarket, I also just wanted to see if it could be done.
 
Is this concept substantially different from what Long Range Automotive sells? Are you just trying to cut cost down?
The fact that it can be done at home (hopefully) is also a big one.

LRA is from a LRA vendor / installer only.
 
I haven't had my GX long but was very interested in this mod almost immediately.
I'm glad to have found someone so diligent and willing to share their findings.

Originally, when I imagined this mod, I assumed it'd be through a 3rd party, but knowing that this is available as an OEM part sounds great.
I have no personal experience with this issue, but while watching professional overlanders (I THINK it was Expedition Overland) one of their many issues when kitting out their vehicles was that the pump that sent fuel to the main tank wasn't triggering correctly. It was fixed in the end and ultimately, I would still consider using a third party, especially to get a professional to install it for me. It does highlight a reoccurring truth - Sometimes, the less steps, the better.

Either way, I think an aux fuel tank is a must for how my wife and myself intend to use our GX.
 
When does the tank arrive @Toyoland66 ?
I suggest reworking your evap plan so that it is serial and not teed. flow from main to sub and then sub to evap. Those evap hoses look very similar to 200, which took 5/8” barb. I’m sure you’ll find a barb that can fit them. After the sub suggest you just convert to the hose size that fits on the canister, likely 3/4”. I think I saw a purple paint hose on the sub filler pic, that will be evap in. The green will be out.

The 200 LRA tees the vent and even though it uses large hoses still has fill back pressure issues in some installs causing the pump to click off. This was y main reason to go with the factory sub tank, I couldn’t imagine waiting for 35 gallons at slow speed on the pump.

Good luck with the project!
 
When does the tank arrive @Toyoland66 ?
I suggest reworking your evap plan so that it is serial and not teed. flow from main to sub and then sub to evap. Those evap hoses look very similar to 200, which took 5/8” barb. I’m sure you’ll find a barb that can fit them. After the sub suggest you just convert to the hose size that fits on the canister, likely 3/4”. I think I saw a purple paint hose on the sub filler pic, that will be evap in. The green will be out.

The 200 LRA tees the vent and even though it uses large hoses still has fill back pressure issues in some installs causing the pump to click off. This was y main reason to go with the factory sub tank, I couldn’t imagine waiting for 35 gallons at slow speed on the pump.

Good luck with the project!
I ordered on the 15th and one of the parts had a 20d lead time, so I’m hoping to receive by mid April.

My plan for the plumbing was to mimic the factory setup, and have each fitting for the main and sub go to the system they were designed for. One thing that is apparent about the US spec fillers is they must expect the charcoal canister to handle some of the venting while filling - the filler vent is only 1/4” while the hose to the charcoal canister is 3/4”. The prado filler neck has a bigger vent, I can definitely see that the LRA would be hard to fill if only venting through the stock filler vent. Alternately, the prado sub tank vent to evap (which is one of the items I already have) is 1/4” or 5/16” (I haven’t put calipers on it) which I don’t know would have capacity for evap venting for both tanks. I will evaluate once I have the tank in hand.
 
I ordered on the 15th and one of the parts had a 20d lead time, so I’m hoping to receive by mid April.

My plan for the plumbing was to mimic the factory setup, and have each fitting for the main and sub go to the system they were designed for. One thing that is apparent about the US spec fillers is they must expect the charcoal canister to handle some of the venting while filling - the filler vent is only 1/4” while the hose to the charcoal canister is 3/4”. The prado filler neck has a bigger vent, I can definitely see that the LRA would be hard to fill if only venting through the stock filler vent. Alternately, the prado sub tank vent to evap (which is one of the items I already have) is 1/4” or 5/16” (I haven’t put calipers on it) which I don’t know would have capacity for evap venting for both tanks. I will evaluate once I have the tank in hand.
Evap is like the dark science of automotive. I could find very little published about the theory of it.

One thing that made me laugh when I pulled it was the size of the orifice on the 'input' side of the evap canister (from the tank), it was 4 to 6 mm!!! This is why for the 200 install I recommend reuse of the manifold hardline to reroute the evap upfront for the canister relo, the actual canister could no way take the volume presented by the 15mm diameter factory tube if it was under any sort of significant pressure.

I don't know why the tube on the US tank is so much larger, I assumed it was so it would 'float' at a very low pressure, but with that small orifice I think it might just be for show. Perhaps there is some EPA rule requiring a minimum diameter of hose.

The 200 sub tank evap hoses are 6 mm, and they transfer to a 6 mm hardline for the canister run (which is forward of the tank but not all the way to the engine bay).
 
Has anyone added a Prado 120 sub tank in their GX470? I know there are aftermarket options available but the possibility of using the OEM tank is interesting and seemingly (possibly?) less expensive. Adding this sub tank increases the total fuel capacity by just over 2x, to 180L/ 47.5 gal.

This tank is an option in non-US markets and I have specifically been looking at the diagrams for the LHD gulf corporation market GRJ120L-GKAGKV which would also have a gasoline (petrol) engine (1GR/ 4.0l V6). It appears this conversion could be possible assuming the tank itself can be found, Partsouq lists it as unavailable so I am checking with a few other places.

Following diagrams are marked up with the parts related to the sub-tank/ parts that denote "sub tank" in their description:

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View attachment 2589050


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View attachment 2589085

You have the tank itself, the mounting for the tank, the plumbing for the tank filler, and plumbing between the sub and main tank. Electrically you have a different main tank pump, and a fuel level float in the sub tank. There is also a different wiring harness that I assume connects between the float and pump. The way the system functions I believe is the rear tank continuously pumps to the front tank with a supply and return plumbed between the two which keeps the front tank full until the rear runs dry, the fuel float in the subtank would control this. I think the vehicles that come with this option also have a different fuel gauge which would read both senders and switch reading between the two, but this may not be easy to retrofit. I am basing this assumption on the following info:



Without retrofitting the fuel gauge it would just continuously read full until the sub tank is empty at which point the main tank would start drawing down.

Challenges:
-Obtaining the parts (tank itself)
-If there is any computer control/ if anything other than the float and pump control transfer between tanks.
-It appears that the main tank is also different (has additional tubes in/ out)
-Charcoal canisters and locations are different

Curious what people think about this. I know adding the sub tank has been done on other series but don't know if anyone has done it on a 120.
the guys in Russia in August 2011 have already installed an additional fuel tank on the Prado 120, if you need any spare parts, I'll try to find them.
If you need a translation from Russian to English, I will try to translate it.
LINK:

 

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