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

[Toyoland66]

I was able to spend a little time this morning without making my family too upset at me.

I got the filler successfully swapped but not without a few snags.

I ordered a new flexible hose for a Prado but discovered that the tank end fitting is larger than the GX.

So due to this I had to result to stretching the original hose onto the new filler which was a bit of a feat. The original filler is 1” and the new is 1 3/8”. I used the @grinchy trick of heating the hose with hot water and stretched it into place.

there are a couple issues that make this less than ideal, due to the thickened rubber I wasn’t able to get the hose on as far as original, however the hose clamp is past the bead so it should come off. the other thing I discovered is that the rubber hose is NLA so if it ends up splitting or otherwise failing that could be a big problem. I think I’m gonna just run with it and address any problems if they arise in the future.

Aside from that removing the old filler and installing the new was relatively painless luckily.

I broke every single plastic fitting holding the fender liner in place, there must have been a trick to removing them but I don’t know what it is. Part 9018906212 I will order some replacements.

 

[Toyoland66]

I was able to focus on the rest of the swap today and had great results.

I started by dropping the main tank. This video has good instructions so no need to repeat them:



One thing I recommend is just go ahead and remove the middle seat and pop open the access cover to unplug the electrical connector. I didn’t have luck trying to unplug it from underneath.

I intentionally drove the fuel level low, the fuel light had been on for about 20 miles. I wanted to make the tank as light as possible so it wouldn’t be too tough to handle. I was able to balance the tank on a floor jack and piece of plywood and there was enough clearance under the framerail to slide it out.

 

[Toyoland66]

New pump and associated parts and part numbers.

Notice the rib here on the locking ring and corresponding arrows that it is supposed fall between. I didn’t have a SST to remove the ring so I used a pry bar with a wide blunt tip and hammered working my way around the ring to not stress any of the ribs too much. It takes about a quarter turn or more before it becomes easy. Don’t forget the little locking tabs as you go (watch the video).

How much fuel was left in the tank.

 

[Toyoland66]

New pump installed in tank. Also note the new fuel feed for the subtank siphon. Also worth noting that the feed and return fittings are front to back instead of side to side. The orientation shown here is correct.

Note here which wires in the plug are for the fuel level sender, this will be important later

They are the two connectors on the wider side of the plug

And on the plug they are these two brown wires

 

[Toyoland66]

One of the tank pads was in pretty bad shape so I replaced it with the tank cushion I ordered for the subtank and ended up not needing.

For The tank vent line I intended to attach rubber hose directly to the tank fitting and delete the plastic vent line. I assumed that this fitting was 1/4” from measurements I was able to get a while back and ordered a 1/4” to 1/2” adapter to adapt this to the subtank vent. Turns out the fitting on the tank is 5/16 so I decided to reuse the plastic line and just cut off the end and insert the adapter fitting into it. A little heating with hot water and it slid right in.

I replaced the vent line to evap with 3/4” hose. I was able to get the hose over the ridge on the fitting so I feel like it’s pretty secure. Here is the tank ready to go back in.

Getting the tank back in was a bit more difficult than getting it out. I had to get it up onto and balanced on the jack from under underneath the car which was a bit of a challenge.

 

[Toyoland66]

Now to prep the subtank to go in for good I had to get the electrical connections hooked up. I was unable to get the wiring harness for the Prado but did find a compatible harness from a 200. The sender fitting is correct but it’s missing the ground connection.

I did have to untape and move the clips a bit, they were putting too much strain on the connection otherwise.

I cut the other fitting off and replaced it with a bullet connector, this is just a single conductor ground wire- I assume to prevent static buildup from the movement of the fuel.

 

[Toyoland66]

Now the subtank is hung and I can make all the plumbing connections. Starting with the vent to evap which is the single fitting on the passenger side of the subtank. This is a 1/4” fitting.

I ran it through this empty fitting on the filler (not sure what was supposed to go here)

I used a tee fitting to tee this into the evap line from the main tank to the charcoal canister.

This is a stainless NPT 1/2 to 1/8 tee and corresponding nipples that I got from McMaster Carr.

These plastic hose organizers all fell apart

 

[Toyoland66]

You probably noticed that the charcoal canister is in the hatch temporarily.

The vent from the main tank attaches to the 1/2” fitting on the subtank. And the remaining 1/4” fitting is the fuel suction tube.

I still need to get some 1/2” hose clamps.

 

[Toyoland66]

The subtank to filler connections. Pretty straightforward

And the tank itself, it hangs down pretty low so I will have to build a good skidplate for it

 

[Toyoland66]

I used these clamps to temporarily organize the lines, there are M6 threaded studs that the stock plastic hose organizers attached to.

And some temporary zip tie work until I get the charcoal canister in its permanent location

 

[Toyoland66]

With all the plumbing hooked up I turned the ignition on and to my surprise the fuel gauge read half full.

I was about to call it a day at this point but decided to take some resistance reading on the stock sender and the new main and subtank senders

Appears that either these senders are intended to be run in series, or I just got lucky and running them in series makes them read like the single tank sender. For those who didn’t read @grinchy thread or aren’t otherwise familiar, when you run resisters in series their resistance is summed.

here is the subtank end connection.

to better explain running the two senders in series, you cut one wire for the main tank sender (I chose the brown with silver stripe but it shouldn’t matter) then connect to one of the cut ends and run a wire to one side of the sub tank sender, then from the other side of the sub tank sender back to the other cut wire. This runs the circuit across both resisters before it goes to the fuel gauge.

 

[Toyoland66]

Problem solved

Now I just have to make it to the gas station without running out of gas. I was able to fill up with no apparent venting issues (no clicking off etc). The only issue I had is that Costco only lets you fill $150 at a time, so I had to restart the pump to completely fill up.

44.67 gallons

And the gauge correctly reads full.

That’s it for tonight.

 

[rommelrommel]

Well, this is looking pretty awesome.

 

[grinchy]

Nice that the gauge reading sorted itself out. I wish the 200 had such a nice solution. I’m still flipping a switch if I want to see the sub level.
What parts of the charcoal can have to be detached? Is it electric only or is there a pump or vacuum device too? Theoretically the items can be separated, they’re just all packaged together to simplify for manufacturing.

 

[Toyoland66]

Nice that the gauge reading sorted itself out. I wish the 200 had such a nice solution. I’m still flipping a switch if I want to see the sub level.
What parts of the charcoal can have to be detached? Is it electric only or is there a pump or vacuum device too? Theoretically the items can be separated, they’re just all packaged together to simplify for manufacturing.

I am sure you already know this, but for others benefit, the purpose of the evap system is to allow the fuel tank to "breathe" during temperature changes while the vehicle is off. The fuel tank is vented through a charcoal canister which contains activated charcoal to neutralize the gasoline vapors for environmental reasons and also so your garage doesn’t stink like gasoline. When the engine is turned on the system closes the vent to atmosphere and opens a valve to engine vacuum that allows the engine to suck the vapors while it is running, on older vehicles this is done with vacuum switches (vsv) on newer cars the switches are electronic (or a combination).

All Toyota’s (in the US) from this era use a leak detection evap system. The contraption attached to the canister is a leak detection pump that draws a vacuum on the entire closed system - gas tank(s), filler and cap, charcoal canister, and all the hoses to ensure the system isn’t leaking. Explained in these videos at greater detail than I care to:





The leak detection pump is on the vent to atmosphere side of the canister, the pump assembly contains a valve that seals off the vent to atmosphere in order to seal the system. It also seals this vent when the engine is running to allow the engine to sucks the vapors out of the system instead of venting to atmosphere.

The pump assembly is removable from the charcoal canister so my plan is to remove the pump, seal the canister and add a hose barb, then seal the pump and add a hose barb. Then I will use a section of 3/4" hose to reconnect the two.

On the canister side I will use a flat plate to make the flange and 3 bolts to fasten it down, and I will use gasket stock to seal it. I ordered a 3/4 x 3/4 90 degree barb fitting and I will weld that in once I determine the best direction to point it. On the pump side I will use a 1 1/2" tube cap to seal against the existing o-ring, weld it to a flange with 2 bolt holes to hold it in place, and weld a 3/4 straight barb to it. I need to figure out a spot to relocate the pump to and not clutter things up too bad.

I cancelled the order for the Prado charcoal canister. Since it is designed to function as a standalone system I wasn’t sure how to integrate the leak detection pump into it.

 

[grinchy]

Ah, ok. Yeah have to link them together. The vacuum that pump pulls isn’t very high, so hopefully the reseal won’t be an issue.

 

[Toyoland66]

I tied up a couple loose ends this morning, I went ahead and removed the trailer plug and wiring from the frame to clean things up a bit. I don’t have a hitch and don’t plan on towing.

I also realized I had ordered 1/2” constant tension clamps for the vent line, so I installed those.

My wife is having surgery Friday so it might be a couple weeks before I can get the evap stuff finalized, just depends on how her recovery goes.

 

[Toyoland66]

Small update. The gas gauge seems to be tracking pretty well so far. Assuming 22 gal +/- per tank and 15 mpg this should be pretty close to 11 gals used/ half empty for the subtank or 1/4 empty for the overall system.

also worth noting that the mpg calculator in the readout above the radio (whatever that is called) isn’t tied into the fuel level senders in the tanks, it meters fuel usage some other way. I know this because i reset it right after the conversion, and it’s still reading the same as before, right around 15 mpg.

also, I know the plastic cover over my gauges is looking pretty rough. I have a new OEM cover in hand, and will install it along with a Dakota digital speedo corrector in the near future.

 

[rommelrommel]

Overall this looks great, would it be possible to take a shot of the tank from one of the sides just to see how far it hangs down past the frame? I have definitely dragged my bumper a few times getting through obstacles and I’m wondering how much clearance I’d be giving up where to put this tank in.

 

[Toyoland66]

@rommelrommel its tough to photograph I’ll have to try again in the daylight

I ran it to empty to get a better idea how the gauge reads and to verify no issues with the evap system. So far no codes have been thrown so that’s good!

I was calculating range based on 15 mpg and it’s a good thing I didn’t go longer before filling up.

That calcs out to 13.28 mpg