Welcome to Bimmerfest -- The #1 Online Community for BMW related information! Please enjoy the discussion forums below and share your experiences with the 200,000 current, new and past BMW owners. The forums are broken out by car model and into other special interest sections such as BMW European Delivery and a special forum to voice your questions to the many BMW dealers on the site to assist our members!

Please follow the links below to help get you started!

Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > Z Series > E36 /7 Z3 (1996-2002)

E36 /7 Z3 (1996-2002)
E36/7 Z3 roadster and coupe talk with our gurus here.

Reply
 
Thread Tools Display Modes
  #1  
Old 04-27-2012, 04:24 PM
z3windsurfer z3windsurfer is offline
Registered User
Location: Oregon
 
Join Date: Apr 2012
Posts: 11
Mein Auto: Z3 1.9L auto
1997 Z3 - 6 fuel sending units?

The sixth fuel sending unit is about to go into my 1997 Z3 1.9L 150,000mi. Most of these have been replaced under warranty from the previous repair. It appears that the rheostat is being cracked. I've finally been motivated to investigate this on my own. I've attached a photograph of the crack. I was told that the two previous to the photographed one were also cracked. I don't recall the situation on the 2 prior to that.

There appears to be no physical damage to the exterior of the tank as inspected on the rack, the tank seems secure although at least 2 of pads between the tank and the supporting straps are missing. Nothing unusual can be seen from the fuel pump opening. When the tank is struck with a fist while on the rack, there might be a rattle sound coming from inside the fuel tank. It is difficult to say for sure.

Has anyone seen a problem with fuel sending units cracking in a Z3 as shown in the photograph? If so, what was the problem?
Attached Thumbnails
Click image for larger version

Name:	CrackInZ3FuelSendingUnit-Edit.jpg
Views:	225
Size:	187.1 KB
ID:	322717  
Reply With Quote
Ads by Google
  #2  
Old 04-28-2012, 03:42 AM
Pinecone's Avatar
Pinecone Pinecone is offline
M Mad
Location: Maryland
 
Join Date: Apr 2002
Posts: 10,482
Mein Auto: M Roadster/M3
Do you top off your tank when you fill it? If so, that can lead to fuel sender failures.

Once the nozzle auto kicks off, do NOT top up.
__________________
Terry Carraway

'95 Alpine M3 LTW
'00 Dakar M Roadster
'02 Topaz M3
Red/White SRF #4 (Chassis 561)
Reply With Quote
  #3  
Old 04-28-2012, 09:40 AM
gpurvis gpurvis is offline
Registered User
Location: US
 
Join Date: Apr 2012
Posts: 4
Mein Auto: Z3
Thank you for the reply.

I don't top off the fuel. This last failure happened on the first tank after a repair. I know that one was not topped off.
Reply With Quote
  #4  
Old 04-29-2012, 04:44 AM
tonywintn tonywintn is offline
Drivin' the dream
Location: Tennessee
 
Join Date: Jun 2009
Posts: 187
Mein Auto: 2005 BMW X5 & 2007 Z4 si
The sender card is made of ceramic. The resistor pads consist of a noble metal alloy paste that is silk screened onto the ceramic. It is very tough and not as brittle as it may seem. It takes a lot of force to break one. And when you do break it, it snaps in half. Yours is very interesting for two reasons: 1) Where did the force come from to break it? 2) How did it break in a curve and not just straight across? You said that you have had previous one break in the same way. Does the white plastic housing have any deformities? e.g. is the back of the white housing bowed in a way that it could have put a load on the card?
Reply With Quote
  #5  
Old 04-29-2012, 06:27 AM
wifesauto wifesauto is offline
Officially Welcomed to the 'Fest
Location: nj
 
Join Date: Jan 2012
Posts: 314
Mein Auto: sloporsche
that is too many units to go through. maybe the unit is not indexed in the tank right or a tank baffle is missing. another way to fix it is to get a complete tank from a salvage yard. you dont drive the baja do you ?
Reply With Quote
  #6  
Old 04-29-2012, 12:35 PM
tonywintn tonywintn is offline
Drivin' the dream
Location: Tennessee
 
Join Date: Jun 2009
Posts: 187
Mein Auto: 2005 BMW X5 & 2007 Z4 si
"Do you top off your tank when you fill it? If so, that can lead to fuel sender failures."- Pinecone,
I am curious as to why you think that.
Reply With Quote
  #7  
Old 04-29-2012, 03:11 PM
Pinecone's Avatar
Pinecone Pinecone is offline
M Mad
Location: Maryland
 
Join Date: Apr 2002
Posts: 10,482
Mein Auto: M Roadster/M3
Because if you search the forum you will see many threads about this happening. It was a very common complaint/issue when the Z3 was still being made and not uncommon in all BMWs.
__________________
Terry Carraway

'95 Alpine M3 LTW
'00 Dakar M Roadster
'02 Topaz M3
Red/White SRF #4 (Chassis 561)
Reply With Quote
  #8  
Old 04-29-2012, 03:20 PM
amancuso's Avatar
amancuso amancuso is offline
Officially Welcomed to the 'Fest
Location: New Jersey
 
Join Date: Jun 2004
Posts: 1,415
Send a message via AIM to amancuso
Mein Auto: 128i, 330i, Z3 2.3, R56
A friend had this problem in his '96. There is a vent tube that was blocked up, causing the the tank to compress, and it would crack/break the sending unit.
__________________

Reply With Quote
  #9  
Old 04-29-2012, 04:30 PM
tonywintn tonywintn is offline
Drivin' the dream
Location: Tennessee
 
Join Date: Jun 2009
Posts: 187
Mein Auto: 2005 BMW X5 & 2007 Z4 si
Well, that would explain where the force came from to crack the card...
Reply With Quote
  #10  
Old 04-30-2012, 06:49 AM
wifesauto wifesauto is offline
Officially Welcomed to the 'Fest
Location: nj
 
Join Date: Jan 2012
Posts: 314
Mein Auto: sloporsche
Quote:
Originally Posted by amancuso View Post
A friend had this problem in his '96. There is a vent tube that was blocked up, causing the the tank to compress, and it would crack/break the sending unit.
very good call...i should have thought of that. i recall GM cars from the 70,s doing that. the tank could look like a pancake. i am old and cant recall my name sometimes
Reply With Quote
  #11  
Old 04-30-2012, 12:17 PM
gpurvis gpurvis is offline
Registered User
Location: US
 
Join Date: Apr 2012
Posts: 4
Mein Auto: Z3
Blocked vent tube

Quote:
Originally Posted by amancuso View Post
A friend had this problem in his '96. There is a vent tube that was blocked up, causing the the tank to compress, and it would crack/break the sending unit.
Thank you! This is an interesting idea. I haven't seen it posted elsewhere.

The fuel sending unit failure is most often noticed after driving about 45 minutes, perhaps decreasing the volume of gas by about 25%. The gas cap is sometimes difficult to remove when refueling, although no in-sucking of air is noticed.

I assume that the gas tank is double-walled. I wonder if the inner wall is more flexible than the outer wall. The outer wall seems pretty rigid.
Reply With Quote
  #12  
Old 04-30-2012, 12:24 PM
gpurvis gpurvis is offline
Registered User
Location: US
 
Join Date: Apr 2012
Posts: 4
Mein Auto: Z3
Quote:
Originally Posted by wifesauto View Post
that is too many units to go through. maybe the unit is not indexed in the tank right or a tank baffle is missing. another way to fix it is to get a complete tank from a salvage yard. you dont drive the baja do you ?
Thank you. I don't drive the Baja or anything close to it unless you consider the degradation of the US Interstate system... but that's another subject.

A loose tank baffle is a possibility. With 5 replacements, I suspect someone has looked at the installation carefully, but you're right, the indexing (orientation) is important.
Reply With Quote
  #13  
Old 04-30-2012, 12:34 PM
gpurvis gpurvis is offline
Registered User
Location: US
 
Join Date: Apr 2012
Posts: 4
Mein Auto: Z3
Rheostat mounting

Quote:
Originally Posted by tonywintn View Post
The sender card is made of ceramic. The resistor pads consist of a noble metal alloy paste that is silk screened onto the ceramic. It is very tough and not as brittle as it may seem. It takes a lot of force to break one. And when you do break it, it snaps in half. Yours is very interesting for two reasons: 1) Where did the force come from to break it? 2) How did it break in a curve and not just straight across? You said that you have had previous one break in the same way. Does the white plastic housing have any deformities? e.g. is the back of the white housing bowed in a way that it could have put a load on the card?
The rheostat is mounted (screened?) onto a polyethylene (well white plastic just like the rest of the pump/sending unit housing) holder. The plastic is cracked through. I tried bending the plastic by hand. It's strong. It would take a lot of force to break it. The wire arm to the float is stiffer than a coat hanger, but has some flex to it.
Reply With Quote
  #14  
Old 04-30-2012, 05:37 PM
z3windsurfer z3windsurfer is offline
Registered User
Location: Oregon
 
Join Date: Apr 2012
Posts: 11
Mein Auto: Z3 1.9L auto
Examination of the fuel tank removed from the 1997 Z3

Quote:
Originally Posted by amancuso View Post
A friend had this problem in his '96. There is a vent tube that was blocked up, causing the the tank to compress, and it would crack/break the sending unit.
So far, your answer seems to be the best.

Today the shop removed the fuel tank. It is a single thick-walled polymer (i.e. plastic) construction. There is no visible sign of external damage or deformation of the tank. Here's a link to an exploded parts diagram for the tank system http://www.realoem.com/bmw/showparts...05&hg=16&fg=05. The round circle in the center is the fuel sending unit/fuel pump mounting port. Part 19 is the fuel tank pressure sensor.

As near as I can tell, there are no baffles in the tank. Certainly nothing loose. The complex shape of the tank may prevent sloshing.

The "rattle" heard when tapping the tank came from a ball valve at the top of the tank that closes the vent to the outside air if the car rolls over. The ball valve and vent casing is bonded permanently to the tank and cannot be inspected for internal damage. It is not possible to tell if there is internal damage.

The tank is also vented through the carbon filter. The on board diagnostic computer shows no error codes typical of a failed carbon canister.

Pressured air flows through the vents now (both the roll-over valve and the carbon canister), so the vents appear to be working normally when the tank is outside of the car. Similarly, all of the lines have tested clear.

Once the inside of the tank was completely dry, it was possible to see light scoring on the inside of the tank directly opposite of the fuel pump mounting port. This wall is closest to the backside of the rheostat. The scoring on the wall matches the protrusions on the rheostat mount that is closest to the wall. The side of the sending unit that is closest to the wall not shown in the photograph. It is on the other side of the rheostat.

With the broken fuel sending unit and pump mounted in the tank, a borescope was inserted down the neck of the fueling pipe. The borescope image showed that the sending unit did not touch the wall and there was 0.25 - 0.5 inch gap between the closest point on the sending unit and the wall. No one seems to be able to say if this distance is "in-spec". Pressing as hard as possible by hand on the pump slightly reduced this distance. The small change in the gap suggested that a collision with the back wall to create scoring would require a large force - much larger than a 170 pound leaning on it.

Sealing the tank and attaching a vacuum demonstrated that the tank could deform significantly with a 3 in vacuum pulled.

Adding these observations to the observations that (1) the problem seemed to appear after driving more than 40 minutes at highway speeds, (2) sometimes the gas cap was difficult to remove and (3) some foam pads for the support straps were missing suggests the idea that a the fuel sending units in this Z3 fail in the following sequence

1. a vent port becomes blocked so pressure can no longer be equalized with the external air pressure, then

2. fuel is pumped out of the tank while driving, creating a vacuum that causes

3. the walls of the tank to collapse inward so that the sending unit's rheostat mounting is resting on the tank wall, and

4. while driving down the road a 70 mph, the car goes over a bump, jarring the half-full tank enough to crack the sending rheostat. It is able to jar the tank because there is a gap created by the collapsing walls of the tank or because there is a 0.25 inch gap between the strap on one side and the tank that came from the missing foam pads.

If this is in fact what actually happens, two remedies can be imagined which are bad ideas from a safety or environmental standpoint and should not be tried:
1. Don't put the gas cap on tightly (warning: a loose cap probably causes other problems)
2. After driving a while, take a rest stop. Take the opportunity to loosen and re-tighten the gas cap thereby restoring atmospheric pressure.

So now the question is what should I do next? One option would be to have the existing tank reinstalled and see if the problem recurs. The second option is to put in a new gas tank so that the roll-over valve is replaced.

I've chosen the second option. Here's my thinking. The existing tank is 15 years old. It is plastic. I like the car a lot. I'd be happy to keep it until gas is no longer available. It still runs well at 150,000 miles and shows no serious signs of mechanical problems as inspected in the shop or that I've experienced. Replacing the tank will never be cheaper than it is now that it is out. Just how long can a plastic fuel tank last? Will I wind up replacing it anyway in the next 10 years?

Will this fix the problem with the fuel sending unit? I'm not sure. I do know that the sending unit is colliding with the opposite wall of the tank and lightly scratching the wall. I do know the sending unit is breaking. I do not see how it could be easily broken during installation.

I've provided this detailed information because the fuel sending unit failure is an often reported problem with Z3's. One could imagine a lot of related scenarios. For example, suppose the contact with the rear wall does not break the rheostat, but simply restricts the motion. The fuel gauge would behave oddly.

If you think I've got something wrong, please tell me. If you have any questions, I'll try to tell you what I've learned, but I'm not a mechanic.

Thanks for taking the time to look at my problem.

Last edited by z3windsurfer; 05-01-2012 at 11:13 AM.
Reply With Quote
  #15  
Old 05-01-2012, 04:31 AM
dougmcintyre dougmcintyre is offline
formerly updmst
Location: Chapel Hill, NC
 
Join Date: Sep 2009
Posts: 659
Mein Auto: 2000 M Coupe, 1997 318ti
If I remember correctly, to pull the gas tank, the subframe has to come out. You should replace the subframe bushings and trailing arm bushings. The labor has already been done.
Reply With Quote
  #16  
Old 05-01-2012, 05:17 AM
wifesauto wifesauto is offline
Officially Welcomed to the 'Fest
Location: nj
 
Join Date: Jan 2012
Posts: 314
Mein Auto: sloporsche
some gas caps have a one way valve.....lets air in not out
Reply With Quote
  #17  
Old 05-01-2012, 09:48 AM
Pinecone's Avatar
Pinecone Pinecone is offline
M Mad
Location: Maryland
 
Join Date: Apr 2002
Posts: 10,482
Mein Auto: M Roadster/M3
Fix the tank vent system.

The tank vents goes to the charcoal canister to capture any fuel vapors when the fuel/air in teh tank expands due to heat. That canister is then vented to the engine while running to burn the captured fuel vapors.

So if the tank is not venting properly, fix the vent system.

And leaving the cap loose with throw a check engine light.
__________________
Terry Carraway

'95 Alpine M3 LTW
'00 Dakar M Roadster
'02 Topaz M3
Red/White SRF #4 (Chassis 561)
Reply With Quote
  #18  
Old 05-01-2012, 10:40 AM
z3windsurfer z3windsurfer is offline
Registered User
Location: Oregon
 
Join Date: Apr 2012
Posts: 11
Mein Auto: Z3 1.9L auto
Subframe removal

Quote:
Originally Posted by dougmcintyre View Post
If I remember correctly, to pull the gas tank, the subframe has to come out. You should replace the subframe bushings and trailing arm bushings. The labor has already been done.
Yes, you remember correctly. The subframe has to come out. That's good advice, I plan to replace the subframe bushings and trailing arm bushings.
Reply With Quote
  #19  
Old 05-01-2012, 10:45 AM
z3windsurfer z3windsurfer is offline
Registered User
Location: Oregon
 
Join Date: Apr 2012
Posts: 11
Mein Auto: Z3 1.9L auto
Charcoal canister

Quote:
Originally Posted by Pinecone View Post
Fix the tank vent system.

The tank vents goes to the charcoal canister to capture any fuel vapors when the fuel/air in teh tank expands due to heat. That canister is then vented to the engine while running to burn the captured fuel vapors.

So if the tank is not venting properly, fix the vent system.

And leaving the cap loose with throw a check engine light.
Apparently, there is a second venting system on top of the tank that closes in a roll over. I'm talking about the box bonded to the top right of the fuel tank core as shown in this breakout diagram: http://www.realoem.com/bmw/showparts...05&hg=16&fg=05. Part 19 is the fuel tank pressure sensor.

According to tests with everything cold and the absence of OBDC codes when it is hot, the charcoal canister system is operating correctly and not a problem. Has something been missed here?

I agree, leaving a loose cap is not a real solution, I mentioned it partly in humor (solve one problem but create another).

Last edited by z3windsurfer; 05-01-2012 at 11:12 AM.
Reply With Quote
  #20  
Old 05-01-2012, 11:00 AM
z3windsurfer z3windsurfer is offline
Registered User
Location: Oregon
 
Join Date: Apr 2012
Posts: 11
Mein Auto: Z3 1.9L auto
Vent in gas cap

Quote:
Originally Posted by wifesauto View Post
some gas caps have a one way valve.....lets air in not out
Good point. I'm not aware that the cap on the Z3 has such a valve. Can't check it now cause the car is in the shop.

Can anyone help on this question?

EDIT: OK, I've found an after market seller (Auto Parts Warehouse) that claims the cap is not vented:

Last edited by z3windsurfer; 05-01-2012 at 11:43 AM. Reason: more information
Reply With Quote
  #21  
Old 05-01-2012, 11:26 AM
Pinecone's Avatar
Pinecone Pinecone is offline
M Mad
Location: Maryland
 
Join Date: Apr 2002
Posts: 10,482
Mein Auto: M Roadster/M3
AFAIK the BMW caps are not vented in any way/
__________________
Terry Carraway

'95 Alpine M3 LTW
'00 Dakar M Roadster
'02 Topaz M3
Red/White SRF #4 (Chassis 561)
Reply With Quote
  #22  
Old 05-01-2012, 11:38 AM
z3windsurfer z3windsurfer is offline
Registered User
Location: Oregon
 
Join Date: Apr 2012
Posts: 11
Mein Auto: Z3 1.9L auto
How over-filling might cause a fuel sensor failure

Quote:
Originally Posted by tonywintn View Post
"Do you top off your tank when you fill it? If so, that can lead to fuel sender failures."- Pinecone,
I am curious as to why you think that.
One thing I've noticed from the exploded parts diagram for the gas tank:
http://www.realoem.com/bmw/showparts...05&hg=16&fg=05
is that the fuel tank filler pipe may extend above the top of the gas tank. Over filling the tank so that the filler pipe is full might flood the atmospheric pressure intake vent causing it to fail. This is just pure speculation on my part, but I've seen over-filling mentioned a number of times over the years as a possible explanation for sending unit failure. However, I've never seen any details for the mechanism of such a failure. I'm just hypothesizing a mechanism.

Please feel free to shoot me down!

Last edited by z3windsurfer; 05-01-2012 at 11:44 AM.
Reply With Quote
  #23  
Old 05-01-2012, 12:00 PM
z3windsurfer z3windsurfer is offline
Registered User
Location: Oregon
 
Join Date: Apr 2012
Posts: 11
Mein Auto: Z3 1.9L auto
Gas cap not vented.

Quote:
Originally Posted by Pinecone View Post
AFAIK the BMW caps are not vented in any way/
Thank you for the quick reply!
Reply With Quote
  #24  
Old 05-01-2012, 02:08 PM
z3windsurfer z3windsurfer is offline
Registered User
Location: Oregon
 
Join Date: Apr 2012
Posts: 11
Mein Auto: Z3 1.9L auto
Preventative steps to avoid fuel sending unit problems?

So I've been thinking about how this problem might be detected before the sensor is broken and what could be done to prevent the fuel sending unit problem.

1. Preemptive replacement of the gas tank is probably a non-starter. It's way to expensive and too much has to be disassembled and replaced. The plastic tank is quite sturdy. The weak point is probably a bonded white cap that feeds (?) the pressure sensing unit (http://www.bimmerfest.com/forums/sho...d.php?t=607871).

2. Checking the metal straps holding the gas tank to the body for missing pads is certainly a good idea. It seems to me at though these are unlikely to fall out without something else serious happening such as a blocked air intake valve that allows the pressure in the tank to fall causing the tank to collapse inward or perhaps some high speed road debris hitting the tank just right. I would replace missing pads immediately and if possible check for air intake valve problems.

3. Since over-filling might be a bad idea, I would be sure not to over-fill. I've noticed that the pump nozzles are shorter now than they used to be. Does that mean that the pump cuts off later than it used to? Are they more prone to over-filling? I have no idea.

Some have said that leaving the key in the ignition in accessory position while fueling can lead to fuel sending unit problems because the Z3's computer gets confused. In that case, they report that disconnecting the electrical (e..g disconnecting the battery) clears the problem. If you try this, be sure that you have your radio unlock code available and you understand that the computer will have to relearn your driving pattern. This process will obviously not fix a cracked rheostat. I also don't believe that it would be likely to cause a cracked rheostat.

Another frequent suggestion to prevent or even to cure a fuel sending unit problem is to run Techron through the fuel system (http://www.bimmerfest.com/forums/sho...d.php?t=392232). Apparently early fuel sensors were subject to build up of deposits on the contacts. The newer fuel sending units use gold plated contacts. I use Chevron Premium. I can't see how this would cause or help a cracked rheostat.

FYI: I my experience, in the process of cracking the rheostat all of the way through, a fuel sending unit may behave erratically, sometimes working and sometimes driving the fuel gage to all the way to the empty-off position. Consequently, it's possible to think that you've fixed the problem, only to have it recur a short time later.

Any other thoughts or suggestions in the prevention arena? (buying a Z4 would be a cute suggestion, but not helpful)

Last edited by z3windsurfer; 05-01-2012 at 02:36 PM.
Reply With Quote
  #25  
Old 05-01-2012, 02:55 PM
tonywintn tonywintn is offline
Drivin' the dream
Location: Tennessee
 
Join Date: Jun 2009
Posts: 187
Mein Auto: 2005 BMW X5 & 2007 Z4 si
I'd say the premise that the vent line was blocked which caused the tank to develop a vacuum and collapse which damaged the fuel level sender is a valid one. So the next question is where and how did the vent line plug? A kinked line perhaps? Could be, or a saturated carbon canister- less likely or a contaminated vent port. Surprisingly, one cause of blocked vent lines is spiders. Automakers started adding screens to the ends of the venting port to keep out spiders. Let's back up a minute and look at the tank venting system. The tank has several vents. Most tanks have two to three vents. They sit at opposite ends of the tank so that the tank has at least one vent port open regardless of the tank attitude- except for when the vehicle is upside down. These vents have roll over valves. The valves will close if fluid approaches their vent lines. It is important that no liquid gets into the carbon canister. So when the car has a full or near full tank and is on a grade, one vent valve is always open. The tank also has another vent valve called the FLVV. This valve controls the fluid height in the tank. The maximum fluid height set by the FLVV maintains a vapor dome inside the gat tank. You cannot overfill your tank. You cannot damage the fuel level sender by filling your tank to the max. This control valve will not let you. Once the tank fuel level is at maximum design height, this valve closes and that causes a pressure buildup in the tank. A sensor in the gas station filler nozzle senses this pressure change and shuts off the gas pump. The gas station nozzles vary, so a standard fill (maximum fluid design height) must be achieved within 1-2 clicks of the nozzle. Beyond 3 clicks is considered overstuffing the tank. Beyond that and fuel will simply start flowing back out of the filler pipe. So stick to 3 clicks max. Don't spill gas on the ground.
The fuel level sender has hard stops at empty and full. That keeps the float arm from banging into the tank top and bottom. Otherwise the knocking sound while driving would make people think someone is trying to break into their car.

Okay, back to the venting. So the tank has multiple vents. These control valves have spring loaded floats inside them so that they close and seal at calibrated fluid heights and stay completely sealed in the unfortunate event of a rollover. Now, the catch is that all of these vents tie into the carbon canister. So all of these vent lines tie into one place. That is so the carbon canister can capture the hydrocarbon vapors and hold them until they can be sucked into the engine and burned. So even during a routine tank fill, all of the HC's stay trapped in the canister. So only air gets out of the gas tank. That is good for the environment and keeps the llberals from outlawing cars altogether. Yes, the carbon canister is a storage tank. HC's go in during a fresh fuel fill and then they go out to the engine to be burned. It goes through this cycle day after day. It doesn't wear out because it is simply a bag of charcoal. Only getting full of liquid gas can damage it. On top of the carbon canister is a vent to the atmosphere. This is where I would suspect the problem to be. If this line got blocked by bugs, mud or kinked somehow then the tank could develop a significant vacuum. As you drive the fuel tank warms up. Just like you said, the engine is consuming fuel, so the volume of fluid is decreasing. Now the car sits overnight and cools down. Input Boyle's Law and you can see why the tank develops a vacuum. Without an open vent line the tank cannot breath. It can and will collapse. The tank grows and shrinks a certain amount already at the temperature and fluid volume varies. That is why the fuel sender is spring loaded. That keeps it on the bottom of the tank at all times.

You said that you blew air through the canister and vent lines, but I am wondering if you could try pulling a vacuum through the canister and vent line, or else blow backwards through the lines and canister. Just to make sure something is not acting like a check valve. I'm worried that you are going through all of the trouble and expense of putting in a new tank and then still might have the same issue again. Just to be clear, I think changing the tank was a good decision considering the stress and compression that the old tank has been through. But it would be good to find the cause of the collapsing tank. One other thought- you didn't back the car over a big rock or something that could have mechanically collapsed the tank did you? (This happens with jeeps sometimes).
Reply With Quote
Reply

Bookmarks

Tags
z3 fuel sending unit 1997


Forum Navigation
Go Back   Bimmerfest - BMW Forums > BMW Model Discussions > Z Series > E36 /7 Z3 (1996-2002)
Today's Posts Search
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On



Forum Jump


All times are GMT -7. The time now is 06:20 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
© 2001-2011 performanceIX, Inc. All Rights Reserved .: guidelines .:. privacy .:. terms