Original text by Jeff Mulchahey
Volume 4, Number 1 - July 1988
The following material is essentially a reprint of an article I authored for the Roundel several years ago. Several Register members have expressed an interest in larger fuel tanks for their tiis arid I am printing a slightly revised version for your information. I imagine that if one were to take a survey of 2002/tii owners, one would find that, after the poor ventilation and air conditioning, and after the painful seats that never seem to slide back far enough, and after the tire and wind noise, the smell fuel tank and the requisite frequent fuel stops are a frustration during long distance touring in a tii. The simple obvious solution to this situation is to increase the fuel capacity of your tii.
In the past there have been three ways to increase the fuel capacity of an ‘02/tii. The first of these was to purchase a 90 liter fuel tank from Alpina. While this tank bolted right into the stock location, it stood several inches taller than stock, had to be filled from inside the trunk, and pretty much rendered the right side of the trunk useless.
Because Alpina stopped making ‘02 parts shortly after dinosaurs became extinct, this option is academic. Option two was to install the 70 liter tank from a factory Turbo. This too required raising the trunk floor substantially as the lower portion of the Turbo tank, as well as that of the Alpina tank, was essentially the same as the stock tii tank and all the extra capacity came in the top portion of the tank. This option is (now is no longer available KK), but the parts are listed in the BMW NA price book and of course the tank ties the fittings for the Kugelfisher injection system.
The third route was to replace the spare tire with an auxiliary 10 gallon tank. These tanks are commonly available but even though my original spare tire has never been on the ground in the past 16 years, I’d get nervous without it.
I was discussing this situation with the good people a Miller and Norburn when they informed me that they were installing the tank from an earlier six cylinder model in the ‘02s. Depending on the exact year and model involved, and thus the tank used, the final capacity was 70 to 75 liters (19.1 to 19.8 gallons). We talked for a while, decided on the appropriate tank, fuel pickup, and level sender, talked some more, and finally decided to order the necessary parts from Germany.
After a modest delay for Miller and Norburn to receive the tank, and a less modest delay for me to get around to installing the new tank, I proceeded with the conversion. This work also gave me an excellent opportunity to clean and repaint the tank well. That done, a new OEM gasket was installed, albeit with the exposed edges of the open cell foam (BMW AG, how could you?) sealed with clear silicone sealant, arid the new tank was fitted into place. Surprise, surprise! The new tank fit perfectly, without alterations to the cutout or the tank mounting holes. All that remained was to install the sender and plumb the injection system. The latter usually involves slip-on hoses and the original lengths may be sufficient but I decided to go all out and have AN fittings welded onto the pickup and to plumb in aluminum Aeroquip hose ends. After that it was just a matter of filling the tank arid driving away... Far away.
There are three other details to be attended to in this conversion. First, the new tank does not have the recess for the OEM muffler. I had taken this into account when I tried a large diameter, low restriction exhaust system fabricated for my car. If you were to perform the conversion, you’d have to replace your rear muffler with a smaller muffler. I would suggest getting the tank first and working around it as opposed to thinking your tiny muffler was small enough and then being surprised.
Second, the tank is taller than original and the trunk floor must be raised, but this time it’s only 0.75 to 1.00 inch. That’s not really significant. You only need 0.75 inch but I used 1.00 inch in the form of several pieces of square 1.00 inch aluminum tubing under the trunk flooring, which did the trick for me arid weigh practically nothing. Third, the new tank lacks the extension up to the fuel filler bolted onto the fender. Thus the original tank’s extension must be cut offend mounted to the new tank with some fuel filler hose, unless for some reason you have a very early ‘02 style filler. Perhaps you could do as I did and find an old, rusted tank to cannibalize.
Thank you, Miller and Norburn -- while preserving your old tank. A nice additional touch of the six cylinder fuel tank is the provision for a low fuel warning light. If you wish, this may be wired as were the European cars, to the red “central warning light”, nee brake failure light on our U.S. cars, on the dash.
The most difficult part of the conversion, if the truth of the matter were told, is raising the trunk floor by 1.00 inch. If you’re like me, you won’t want to raise just the tank cover. Rather, you’ll want to raise the entire floor in order to keep it flat. I’ve already mentioned the aluminum bracing around the sides of the trunk floor. I also reinforced the spare tire cover with some 1.00 inch tall x 0.75 inch wood strips and reinforced the tank cover with several 0.25 inch tall x 1.00 inch pieces. That wasn’t tough but you may have to hit the local hobby store to find pieces which are dimensionally accurate.
The front portion of the trunk doesn’t have a even floor so I made one from a 29x1 1 inch piece of 0.25 inch plywood on 0.75 inch tall x 1.00 bracing end covered it to match the rest of the trunk. This raising of the floor will also allow you to accommodate a 185/70x13 tire in the spare tire well; you’ll have to alter the height of the spacers on the bottom of the spare tire cover to accept the wider tire. If you increase the aluminum section to 1.25 inch and elevate the other components accordingly, you can hide a 195/50x15 Pirelli P-7 spore one 6 inch (Alpine) wheel in the spare tire well.
Another detail you might want to attend to is that the right side belt securing the differential mount to the body cannot be withdrawn past the new tank—rather like the famous tii alternator mounting bolt versus the radiator. If your car was put together as mine was, remove the bolt from the rear prior to installing the new inches taller than stock, and reinsert it from the front.
All told the tank makes a terrific addition to a terrific car. The tank itself was a breeze to install. The larger tank is approximately one inch lower than the old tank but most of this is in the area just behind the rear wheels so that the ramp clearance is not affected. Aside from fill-up time you’ll probably never notice the extra volume of the new tank. And if you’re careful, you’ll probably never notice that the trunk floor has been elevated ever so slightly. My new tank is rated at 19.8 gallons although because I’ve never run it dry I’ve only put 17.5 gallons into it. Nevertheless, that is still good for over 400 miles on a cross country run.
I was fortunate that the larger tank matched the original space so well. However, I understand that on some years or models the tank cutout in the trunk floor may have to be enlarged or a mounting hole on the tank altered. Basically it is my understanding that one merely takes the year and type of ’02 (i.e. injected or not) and converts it to the same year and type of appropriate six cylinder model and installs that tank in your 2002.
