Tankzilla problems, fixes & observations (long as usual)

["Walter" <Whalt@xxxx>]

I've had a variety of problems getting all the bugs out of my Tankzilla.
The nice thing about the Zilla products is that the vendors stand behind
them and are quick to resolve problems. So far the problems I've had
involved leaks, fit, and function.

My Tankzilla leaked for 2 reasons. The most prominent leak was from the
construction of the top. Just under the metal lid is a centering ring that
is spot-welded to the top in several places. Between the spot-welds there
is no seal and plenty of room for fuel to leak out. These gaps were even
big enough to slide several thickness of paper through, so it's no wonder I
had leaks. How I fixed these leaks was I cleaned the surface with a spray
can of disk brake cleaner and then filled the gaps with JB-Weld epoxy. The
use of a heat gun and a knife blade helped to get the epoxy completely
through the spaces. The second reason for my Tankzilla leaking was due to a
faulty gasket. New out of the box, the gasket was pliable. But after a few
months of being exposed to fuel washing over it due to the above mentioned
leaks, the gasket turned as hard as plastic. A possible contributing factor
was that the outer diameter of the gasket was barely wide enough to cover
the key-way notch in the tank opening. I made a new gasket out of chrome
tanned tooling leather. You can gasp all you want, but if you understand
materials, leather is a great choice as it is difficult to find a material
that is 'crushable' enough to provide a good seal, yet inert enough to not
be affected by fuel. FYI, my Lincoln floor jack originally came with
leather seals that lasted a lot longer than any rubber ones I have put in
there since. The supplier told me that leather was no longer available due
to animal cruelty laws, yet leather seats are still very popular. Go
figure! My second choice for a gasket was the original rubber seal from my
locking gas cap since I'm not using it any more and it is coincidentally the
same outer diameter as the Tankzilla requires, but I preferred to save that
for museum purposes. DMC Joe recommended that I just fill the gaps with
Permatex Form-A-Gasket. I didn't do this because I was worried that the
gaps were too big and there was too much fuel sloshing in that area. I
think it would eventually wash out the material.

I've had 3 problems with getting the Tankzilla to fit properly. The first
problem was that the electrical connections on the top of the sensor sat up
too high and wouldn't clear the access cover. Rotational orientation of the
sender made no difference. I've read a post from another DMLer about having
leaks through the electrical connections, so if yours leaks through there
then it may be from mechanical wear caused by the access cover. To get more
clearance, I bent the male spade lugs on the sensor to the sides and removed
the female spade connectors from the plastic socket and insulated them with
heat shrink tubing. The second problem I had with fit was caused by the
fact that the hole in the tank for the fuel sending unit wasn't centered.
The top lip of the Tankzilla is a speck wider than the OEM sender and made
it very difficult to screw the retaining ring down. At a later time when I
had the fuel tank out of the car, I used a rat tail file to make the hole a
little bigger and better centered. The third problem with fit was that the
Tankzilla is missing the key-way that the OEM sender has. This is really
inconsequential other than making it hard to choose the orientation of the
electrical connections because the sender unit rotates in the hole as you
tighten the retaining ring.

The problems that I've had with the Tankzilla's function I've been able to
mostly resolve. My initial complaint was that the sending unit was much too
sensitive to fuel sloshing in the tank. It caused the fuel gauge to differ
by more than 1/4 tank while turning, stopping, accelerating, etc. When the
car was low on fuel, the low fuel warning light would blink wildly. I
called Rob and asked him what he thought of this. He said that on previous
Tankzillas he would put rivets in the lower holes on the sending unit to
slow fuel movement around the float. He said that he quit doing this due to
various reasons. I did some calculations and found that the lower half of
the Tankzilla has about 8.5 times more cross-sectional area for fuel to pass
through than on the OEM sending unit. This easily explains the wildly
fluctuating readings. I tried to resolve this by making a second baffle
that would surround the Tankzilla. My design was a large beer can -- of all
things. I choose this because it was already the right shape and is
impervious to the effects of fuel. It sounded great in theory, but when I
tried to install it I found that there was very little room for it in the
tank. The fuel sending unit almost touches the bottom of the tank and is
very near to the front edge were the bottom of the tank curves. There just
wasn't enough room. So I scrapped that idea and went filling the holes in
the lower half of the Tankzilla with JB-Weld epoxy. The only holes left now
are the 3 slots in the plastic base of the Tankzilla, yet these together
still have 2.5 times more cross-sectional area than the OEM sending unit.
My fuel level readings are much more stable now, and the low fuel light
doesn't flash quite as bad. But there is still room for improvement. I
plan on filling 1 or 2 of the remaining 3 openings, and this should do the
trick.

For those of you who want to try any of this, be very careful while
disassembling the Tankzilla. It uses a single nickel-chromium wire loop
that is extremely fragile. Do not allow it to scrape or touch the sides of
the aluminum housing as you take the unit apart.

Some observations I had while working on the Tankzilla is that it's
operation is very different from the OEM unit. It looks like someone got
very lucky in finding a sending unit meant for a different application and
was able to make it work in the DeLorean. Just for curiosity sake, I would
like to know what application this sending unit was originally meant for. I
s anyone willing to say, or is that a trade secret? It was made by the VDO
company in Germany. I know they make a lot of quality aftermarket gauges.

How the Tankzilla differs from OEM is that OEM uses a coil of resistive
nickel-chromium wire. As the float moves along the coil, the resistance in
the unit changes. When empty it gives 0 Ohms, and when full it gives 100
Ohms with 90 Ohms being equivalent to the 4/4 mark on the fuel gauge. The
Tankzilla unit uses only a single loop of wire rather than a coil and works
in reverse with 0 Ohms being a full tank and 64 Ohms being empty. The
interface box that comes with the Tankzilla inverts and expands the scale to
match the OEM unit. This was quite a feat of engineering, and I applaud
whoever designed it.

In order to improve the function of the low fuel warning light, the
Tankzilla has a built in 3 second delay before it allows the light to come
on. Unfortunately this advantage is more than lost due to the large volume
of fuel that can slosh through a stock unit. But if you block most of the
holes, this won't be a problem.

At this time the Tankzilla is the only new fuel sending unit available for
the DeLorean. So if your OEM unit fails, your main choices are relying on
your trip odometer or installing the Tankzilla. In some cases the OEM unit
can be repaired, but it is just not a good design to begin with. I would
like to see someone design a solid state fuel sending unit that uses
inter-electrode capacitance. It is very do-able and could be retailed for a
whole lot cheaper than the Tankzilla, but I've got way too many other
projects in the works. Does anyone else want to take a stab at it?

Walt Tampa, FL