Rumbling noise from within gas tank

[phildg2000]

Hi again!

While checking my brother-in-law's '89 525i, I noticed a rumbling noise from the rear. At first, I thought it was tranny related. So, i have the car lifted and start listening for the noise. I zero in on the gas tank and it seems to be coming from inside the tank. Fuel pump comes to mind. Maybe it's gotten loose in there? Engine performance seems to be normal. Any insights?

Thanks,
Philip

[Bimminator]

Hi again!

While checking my brother-in-law's '89 525i, I noticed a rumbling noise from the rear. At first, I thought it was tranny related. So, i have the car lifted and start listening for the noise. I zero in on the gas tank and it seems to be coming from inside the tank. Fuel pump comes to mind. Maybe it's gotten loose in there? Engine performance seems to be normal. Any insights?

Thanks,
Philip

You might want to check the sender unit. I just had my tank refurbished last month or so and when my indy took out the sender and the pump, the sender was actually in two pieces. I would suspect that first, in your case as the pump is held in-place by a plastic basket of sorts so it is not likely to be "loose in there". This is very easy to check, wait until your fuel level light comes on then clean out your trunk, vaccuum the area around the access panel, then take the nuts off the top of sender unit. If sender is original they may be seized, soak them with penetrating oil a few days in advance. The sender then can be pulled right out, careful not to mix up fuel ines if you disconnect them. Check archives under fuel pump, Bruno has a really thorough write up on this.

[laguner]

The fuel pump on these cars is pretty loud. If you can only hear it outside the car, that is not a problem necessarily. If it is audible inside the car, that would indicate an issue but sound is hard to determine over the internet.

[shogun]

Remove the tank lid. If it makes a hissing sound, the de-airation does not work. A big problem on E38, some tanks were damaged by that vacuum inside the tank.

[Kalevera]

These senders will get very loud as the primary fuel filter (really just a pickup screen between the fuel pump and the tank) gets clogged up with junk. It can be cleaned (pull the sender, use a rubber glove and remove the plastic "basket", as previously mentioned -- it's held in with two tabs...press inward). The noise is attributed to the pump doing more work than it has to, so if it isn't cleaned, the pump can be expected to die in less time than normal.

best, whit