Fuel Tank Frenzy

Update by Scott Lear to the BMW 325is project car
Nov 20, 2007

Our first eBay purchase was for the wrong part; if you’ve got a pre-1987 BMW 325is, you want the BM1A gas tank with the nubs on the bottom near the driveshaft. The BM1A also has dual hard lines on the top. We’ve got a 1989, so we sent this BM1A back and ordered a BM1B fuel tank.
The BM1B has no connecting nubs near the driveshaft, and just one hard line up top. It’s also a couple of gallons bigger than the BM1A.
Even after draining the tank most of the way, it’s good to have a gas container handy to hold the runoff from connections, like the filter.
Label each line and hose. You’ll be really glad you did when it comes time to connect everything back up. When in doubt, be descriptive; for this mess of connectors, we used TO FILTER, FROM FILTER, UP THROUGH TANK and TO LOWER TANK NUB and it saved us lots of headaches later.
It’s also wise to take pictures of stuff to help you get it back together again. This is the top of the in-tank fuel pump. We ended up labeling these lines, too.
For 2008 we’ll need a soon-to-be-released spec exhaust anyway, so we got lazy and just Sawzalled the old one downstream of the O2 sensor so the car is still drivable in the meantime. Oddly enough, after we cut the twin pipes, a short length of pipe between our cut and the catalytic crossover replace
With the driveshaft and exhaust out of the way we were able to undo the five bolts that hold the fuel tank in place. If you’re using jackstands, make sure they’re towards the back edge of the jack point or the tank won’t be able to fall.
We gently negotiated the new fuel tank into place. Mercifully, all the pre-drilled mounting holes were pretty accurate; we had to do some nudging to get the final two bolts in their holes, but no re-drilling was necessary. Not bad for a cheap eBay find!
While we were at it, we installed a new fuel pump and a new filter. Here’s the pump/fuel gauge sensor assembly. Don’t forget to lubricate the O-ring with gas before you install a new fuel pump, and it’s worth noting that the reason this is a two-part assembly is that the pump won’t go into the tank
With everything bolted up and tightened down, we poured a couple of gallons in, crossed our fingers and fired it up. Finally, some positive progress, as the fuel pressure at idle is where it should be instead of at 90 psi.
While were were down there, and getting intimate with the various fuel and brake lines, we noticed that our rear brake line has a small pinched area that could very well be the cause of our rear brake locking symptoms. Rather than going right for the ABS pump, it looks like our next logical step is

Cleaning the OEM tank seemed to be the cheapest way to go, but our tank also had some dents in the bottom, and without cutting it open there was no way to tell if the line was clogged with goo or physically crimped.

If you remember from our recent Ocala test, our car’s perpetual rich-run condition seemed to be related to a clogged or restricted fuel return line. We were seeing 90 psi of fuel pressure at idle, as the fuel coming from the pump had nowhere to go once it was done feeding the fuel rail. It wasn’t the fault of the fuel pressure regulator (we replaced that), and the line was found to be clear as far back as the entry point to the fuel tank. That meant that the line was messed up somewhere inside the fuel tank. Unfortunately, that meant it was time to take the tank out.

Our two options were to remove our stock fuel tank and get it cleaned or to buy a new tank. Cleaning the OEM tank seemed to be the cheapest way to go, but our tank also had some dents in the bottom, and without cutting it open there was no way to tell if the line was clogged with goo or physically crimped. Cleaning might not have fixed anything. Most of the replacement tanks we found online were going for more than $300, with OEMs listed closer to $500.

That’s when eBay came to the rescue. It took a bit of digging, since searches like “BMW 325 fuel tank” didn’t work, but when we got specific and searched for “BMW 325is gas tank” a shop called The Radiator Connection popped up. They had both the early BM1A and later BM1B tanks listed, the former for $100 and the latter for $130 (plus about $40 shipping in each case). Naturally we were skeptical of the low price, but the seller had more than 17,000 transactions and a 100 percent positive rating, so we figured it was worth the gamble.

A miss-read on our part led us to first order a BM1A tank, which is for the earliest 325is models. We actually needed a BM1B, so we returned the earlier model tank after taking some pictures for posterity. In both cases we had tracking numbers for the packages within 30 minutes of placing the Buy It Now bid on eBay. We added our own positive ranking to the seller’s 100 percent streak.

The eBay tank was a dimensional match for the OEM one, although it lacked the small plug at the bottom of the passenger’s side that can be used to drain the tank. For what it’s worth, our OEM tank’s plug was completely frozen in place anyway. We drained most of the fuel by MacGyvering up an extra long hose off the fuel return nipple on the fuel pressure regulator running it into the fuel tank of one of our other cars. (If you do attempt this, refrain from smoking, please).

Replacing a gas tank is a messy chore, as it requires the removal of the exhaust as well as the driveshaft. Also, get used to smelling like gasoline, as it’s nigh impossible to completely prevent spills as you disconnect the many lines carrying fuel hither and thither. Label lines and hoses as you go, and take the opportunity to replace any worn looking hoses with new replacements. Just make sure that you use fuel injection hose for the pressurized lines; we bought two feet of the stuff (about $10 at Pep Boys) and that was plenty for the three or four hoses we replaced. Since the OEM hose clamps are of the cheap single-use variety, buy a bunch of stainless screw-type hose clamps as well and replace as you go.

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