Tembo / Exel 15 gallon Aux Tank Installation

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My 2cents and I did consider this before taking this journey-

You are correct, Kalifornistan does require a carbon canister with an active purge cycle via engine combustion for every 34 gallons of fuel to be CARB compliant- Not applicable in my case.

The Tembo solution is a closed loop system with the OEM. The OEM Evap is working as design to capture evaporative fuel and burn it off during the engine combustion cycle. The vehicle passed Missouri emissions test with no issues.

You are correct based on a 1972 regulation an aux tank is not allowed to gravity feed directly into a carbonator or injector. Federal Motor Carrier Safety Administration, DOT states that "Gravity or syphon feed prohibited. A fuel system must not supply fuel by gravity or syphon feed directly to the carburetor or injector. " This solution does not feed the engine fuel delivery; it fills the main tank. (The FMCSA misspelled siphon... )

Regarding, fuel transfer pung location- it is legal as it does not protrude more than 2 inches from the tank. I share your concern when I eyeballed it the first time yesterday; I am having the shop build a protective sheld/skid plate. The gravity feed line is rubberized steel belted fuel line that the shop further protected in a solid wall corrugated loom tubing. I am confident that the solution is in compliance with a 45 year old set of regulations.

Regarding FMVSS No. 301, the placement and fitment of the tank, and the sure mass of ARB steel bumper and the LC200's rear cross member, plus the Exel tank design- I am more worried about the soul that rear ended me at 30 mph than any damage to the aux fuel tank. Being rear ended once before with the gal traveling above 30, the OEM bumper body pop off, and the tail gate was damaged, but that was about it- Regarding, safety venting all OEM venting remains in place, and the theory operation of this solution does not compromise its function.

Regarding VESC-22, check. This implementation is in compliance. "The fuel connections from the auxiliary fuel tank to the primary system, including a selection control valve, shall not render inoperative any of the functions of the primary system. The auxiliary fuel tank lines, fittings, valves, and connections shall, for purposes of fuel flow, be of a size at least equal to the primary system."

This solution has no selection valve as is it passive.

Final thoughts, this solution mimics the OEM sub tank function as much as possible although the tank is better built. I would rather carry 15 gallons of fuel in this manner than 15 gallons on a roof rack any day.
 
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For the sake of fun and the reading enjoyment of others- Here in the free state of Missouri (smile) physics apply, fluids leaving a vessel under the natural force of gravity do so through a drain. For a fluid to be withdrawn against the force of gravity a pump would then be required. My stance this Aux drains into the main-
 
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george_tlc said:
I may be totally confused here.... but are auxiliary tanks that gravity feed a main tank even LEGAL in the US??? From my understanding it is illegal to have an auxiliary tank that feeds petrol out from a bottom bung, i.e fuel must be pumped from the top of the tank to transfer it.

Not sure if any of you folk care, but just raising a concern if you have a) inspections and/or b) have a major leak at some point and insurance is involved...

cheers,
george.
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Good question. Whatever it is...I'd wager that *enforcement* massively differs by state.
If Kalifornistan had its way? -You wouldn't even be allowed to have the MAIN tank... :bang:
 
Hate to be boring... not really I have driven 125 miles since pick up and the fuel gauge still says full. (Yes, I am pretty happy as this would normally mean a 2/3 empty tank) Other than that not really- I did order a scan gauge II I miss the distance to empty function and want to see if I can fake the scan gauge into calculating DTE- I will be adding some armor to protect the gravity "drain" and gravity fill line. I guess right now I am looking forward to the fuel gauge to dip below full- most likely in next 50 miles or so.
 
Forrest Murphy said:
Hate to be boring... not really I have driven 125 miles since pick up and the fuel gauge still says full. (Yes, I am pretty happy as this would normally mean a 2/3 empty tank) Other than that not really- I did order a scan gauge II I miss the distance to empty function and want to see if I can fake the scan gauge into calculating DTE- I will be adding some armor to protect the gravity "drain" and gravity fill line. I guess right now I am looking forward to the fuel gauge to dip below full- most likely in next 50 miles or so.
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Thanks for sharing your experience, and taking the plunge. Since you mentioned the scan guage, I was wondering if you (or anyone else) considered whether re-programming the ECU/ECM could - in theory - prevent codes from being thrown from a larger tank. So much of what people have tried is centered around addressing the ECM specs, just wondering if anyone knew if those parameters were adjustable.

Or is doing that simply beyond the pale for someone who wants to retain a legal, on-road vehicle?
 
Scan gauges are generally only read only monitors. They can reset and clear the ECU of codes. They don't have any ability to program, especially Toyota's.
 
TeCKis300 said:
Scan gauges are generally only read only monitors. They can reset and clear the ECU of codes. They don't have any ability to program, especially Toyota's.
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True. I think you need access to the Techstream TIS system that Toyota uses for ECU re-programming:

Requires a subscription: https://techinfo.toyota.com/techInfoPortal/appmanager/t3/ti?_pageLabel=ti_whats_tis&_nfpb=true

And the machine itself isn't cheap: https://techinfo.toyota.com/techInf...75566?_pageLabel=ti_vehicle_reprog&_nfpb=true

But would be very interesting to know how open the software actually is, i.e., whether the parameter around fuel system pressure is itself adjustable. Maybe someone with a dealer buddy could find out... :-)
 
Aftermarket companies and individuals have been trying to crack Toyota/Lexus ECU's for decades to tune engines for aftermarket parts with the stock ECU. Just about every other major manufacturer like Honda, Subies, BMWs, Porches, etc. has been cracked or backwards engineered. Not the Yota's. Not even the dealership, unless it's a manufactured allowed select-able option.
 
3 fill-ups no issues, no codes. Today was the first day above 90F so any of my concerns about ambient temperature changes impacting the install seem to be a non-issue at this point. As it gets warmer in the coming months I will report back.

This is the first time I have driven to point of the fuel warning light coming on. This fill-up I saw 374.1 miles and using 35.6 Gallons. 60% city / 40 %HWY achieving 10.56 MPG. On the highway, I normally see about 12.5 MPG fully laden so the same 35.6 gallons would achieve a 450-mile range without dipping into the main tank reserve.

Observation: I have noticed when using filling stations that do not have fuel vapor recovery system built into the pumps I have to "burp" the system- basically slowing and occasionally pausing the fueling to allowing the air in the tanks to escape. When using a station with fuel vapor recovery system filling the tanks slowly works without pausing the fueling process.


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Nice to see the system working to expectation.

If you don't mind me asking, how much are you in on this mod? I wouldn't be surprised that you're close to $2k in?

If this mod could be done under $1k, I suspect there would be a much larger audience for the mod.
 
The Exel tank sourced through Tembo cost approximately 1200 USD international air freighted via UPS to my door. One could save some on shipping if you choose a slow boat and/or a group-buy. The Exel tank is a well-manufactured tank plus the kit comes with all the hoses, fittings, clamps for the gravity tank integration to the main. A custom fab shop could build something similar for a little less.

I had a trusted shop do the install which worked out to be about 35 hours of work for the tank install and EVAP relocation (mounting bracket and a custom skid plate (4.5 hours). I ask they drop the main tank to perform the integration, a more cavalier approach might be able to save on this step which would cut about 12 hours. I had concerns the US spec URJ200 might have some unknown difference in the tank, the fuel sender, the fuel jet, etc. This also allowed the tech to choose the optimal placement of the gravity drain (feed), to ensure a tight seal and clean up the main tank from drilling the hole.

As a side note, the shop also tested the installation through running 1.5 tanks of fuel or about 500 miles of driving. In fact, there have been 4.5 tanks of fuel through the system.

Future installs of a similar nature could be done in less time using some of the explorations from this effort. 12-15 hours of the install was trial fitting to arrive on the final installation, knowing now the Tembo instructions are accurate I think most of this time can be shaved off.

Regarding ROI of the install- well being able to drive on open highway for 450 miles without having to stop for fuel, having to fill once every 2 weeks at most vs weekly when driving around town, and minimizing fuel stops on road trips as even gas and go fuel stops in our family takes 45 minutes- I view these as priceless.

It makes the taking the 200 less of a trade off-

I guess mitigating the three big OEM white spaces with the US URJ200- brakes (stop tech), suspension (kings shocks and king springs), and fuel range (Tembo)- the 200 now has no compromises.

Put simply, no regrets.
 
I know some of you are considering an Aux tank upgrade, so I will share a 6-month update regarding the Tembo- no issues to report. Boring.

Averaging about 405 miles to the fillup- Once saw 525 miles downhill from the mountains and across plains of eastern co and western ks with a 25+ MPH tailwind. There was a little pucker factor as we used 38 gallons of the 40.4 for no other reason to see how far we could go. As laughable as it is I was hypermiling a 7800 lb+ 200. I read somewhere that one can gain 1-1.5 MPG by installing a snorkel, so that is next mod (smile)-

The rig passes safety and emissions- passing all nine emission tests including the EVAP self-test- I have learned through experience that the EVAP test runs after defined driving pattern, after 8 hours from shutting down, requiring a cold start and when the main tank is between 1/4-3/4 full. I find my self rarely dropping below 3/4 in the main, +/- 20 gallons used, as I have to refill gas cans for our yard equipment about every two weeks, so I fill the 200 at the same time.

The only downside to the installation the kido's bladders, heck even mine, twice we had to stop on a 1000 mile road trip on the shoulder of the interstate as no exits where readily available. Yes, twice good folks stopped to make sure we were okay- they saw the boys having a distance contest. The protracted conversations regarding the rig and overlanding with the two sets of good samaritans negated any time made not stopping to fill up every 2.5 hours.

so I kid you not I fix this- and the fix works.

https://www.amazon.com/ZUPONT-urinal-Ltr-duck-Care/dp/B00YM2R67W/?tag=ihco-20
 
Forrest Murphy said:
I read somewhere that one can gain 1-1.5 MPG by installing a snorkel, so that is next mod (smile)
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I've seen zero difference in mileage with the snorkel (which was no surprise). It adds +50bhp though ;-)
 
cool mod and experience for all to learn - good job man!
thank you for sharing
 
The fill path between the two tanks is the same as OEM size between the fill neck and main tank. I have found gas pumps with fuel recovery systems intergrated there is no issue filling at full tilt- but at the 16 gallon mark or so I have allow the system to burp by taking a pause filling for about 30-45 seconds- Fuel seems to be able to fill faster than the air can escape when it displaced.
 
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