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Thread: Cracked Piston

  1. #1
    Join Date
    Jul 2016
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    1995 BMW 325 IS

    Cracked Piston

    Hello group,
    I have a 1995 325IS.
    It will overheat.
    I have replaced the water pump and thermostat.
    Ran compression tests, found a cracked piston.
    The car runs great for a good 10 minutes (no problems).
    Then it overheats.
    Trying to decide what to do with the car.
    Since it runs good for 10 minutes on start up, should I scrap it?
    I love my little car.
    Hard to gage the compression test. Running around 90psi doing "the normal" compression
    test. Only running about 10-20 psi following BMW's recommended compression test.
    I'm wondering how long the piston has been cracked and if this is really the problem.
    Ordered a new radiator cap cause the current one is cracked a bit. Also replaced the overflow
    tank as it cracked when first overheated (I think). There is talk of the
    fan not kicking on when it should-causing it to overheat???
    Obviously could be a blown head gasket or cracked block.
    NO MOISTURE ON TOP OF THE PISTONS, NO RADIATOR FLUID WHERE IS SHOULDN'T BE.
    NO MOISTURE IN THE OIL.
    However, we have not removed anything other than the sparkplugs for visual inspection and
    pressure testing.
    Thoughts?? I would hate to scrap my cute little car if this could be something simple that we
    haven't explored.

  2. #2
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    why would you think one of the pistons is cracked?

  3. #3
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    Well first make sure you've bled the system properly after the coolant system work. Would be nice if that's the reason for overheating.

  4. #4
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    Shot a camera down there.

  5. #5
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    Quote Originally Posted by Nanniepoo View Post
    Well first make sure you've bled the system properly after the coolant system work. Would be nice if that's the reason for overheating.
    Yeah, in a perfect world, that would be great!
    I'm sure it's been bled properly.

  6. #6
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    Buy a $500 M50 or M52 and swap it in.

  7. #7
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    Are you trying to figure out if the motor will work with a cracked piston

  8. #8
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    Jun 2010
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    1997 328i
    C'mon people the piston isn't cracked, that's just what some wannabe BMW mechanic said.

    Lorrie, the engine needs a new cylinder head.

    They crack and warp when the engine overheats, could have been failed water pump, coolant leak. A bad fan is just an additional item on top of a neglected car.
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  9. #9
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    PISTON.jpg
    Quote Originally Posted by Eric93se View Post
    C'mon people the piston isn't cracked, that's just what some wannabe BMW mechanic said.

    Lorrie, the engine needs a new cylinder head.

    They crack and warp when the engine overheats, could have been failed water pump, coolant leak. A bad fan is just an additional item on top of a neglected car.
    Piston #2 has a crack in it. We have a camera and looked at it in the garage. New water pump and new thermostat installed after overheating started.
    Yes-I would like to know if it possible to drive with 1 cracked piston, but still need to determine the root cause of the overheating.
    Not sure how long I've been driving the car with the cracked piston. Like I said, the car runs great for the first 10 minutes, then overheats???

  10. #10
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    Quote Originally Posted by lorrie View Post
    Yeah, in a perfect world, that would be great!
    I'm sure it's been bled properly.
    Do you know or don't you?



    Sent from my LG-H872 using Tapatalk

  11. #11
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    does the cracked piston even have any relation to the overheating issue?

  12. #12
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    Quote Originally Posted by samy01 View Post
    does the cracked piston even have any relation to the overheating issue?
    That is what I was wondering.
    If the head is cracked, you would think it would run terrible on startup, or not startup at all.
    It doesn't lose any coolant, no coolant in the oil or piston area.
    Yes the car runs good for a solid 10 minutes and then overheats.

  13. #13
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    I don’t think it’s because of the piston. I think you warped or cracked the head or blew the gasket on the overheat. Anyway,when you pull the head,you can look at the piston more closely.

  14. #14
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    Do you think it's possible to blow the head gasket and still not have any of coolant
    going where it shouldn't?

    Thanks everyone for the comments.

  15. #15
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    Quote Originally Posted by lorrie View Post
    Do you think it's possible to blow the head gasket and still not have any of coolant
    going where it shouldn't?

    Thanks everyone for the comments.
    You could have exhaust gases getting into the coolant. There's fairly cheap (I think) strips you can buy to test your coolant

    Sent from my LG-H872 using Tapatalk

  16. #16
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    Quote Originally Posted by Nanniepoo View Post
    You could have exhaust gases getting into the coolant. There's fairly cheap (I think) strips you can buy to test your coolant

    Sent from my LG-H872 using Tapatalk
    Great idea! Thank you very much!

  17. #17
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    Quote Originally Posted by lorrie View Post
    Do you think it's possible to blow the head gasket and still not have any of coolant
    going where it shouldn't?

    Thanks everyone for the comments.
    Most of the failures seem to be combustion pressure getting into the cooling system and pressurizing it.

  18. #18
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    The crack will expand and open when the car warms up, then combustion gases go where they shouldn't heating things up a lot.
    Attn. NEWBIES: Use the search feature, 98% has already been discussed.
    Click the search button, select "search single content type", select the "e36 sub forum" specifically, try the "search titles" then try the "search entire posts".

  19. #19
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    Update:
    We did an exhaust gas coolant test last night-it didn't show any problems.
    This is embarassing-checked the fuses for the coolant fan-1 was blown.
    Replaced the fuse, the car ran for a good 20 minutes w/o problems last night.
    Still not sure if out of the woods, but wouldn't it be nice to be a stupid little fuse?
    What scares me is that I wonder how many mechanics would have charged a fortune and told me to scrap the car.
    We also put a new radiator cap on-the old one had a crack in it.
    Let's hope that dang piston crack stays put. I'll try to run the car longer tonight.
    Thanks to everyone for their input and advice.

  20. #20
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    It makes sense to try everything else before doing a headgasket change, but you do have a 22 year old iron block aluminum head motor that has been overheated.

    Many have been down this road, and find something like a questionable tank or cap or WP or fan and change it hoping it will be the fix. Many have found no coolant in the oil or vice versa. And many have done the exhaust gas coolant test and found nothing.

    The auxiliary fan turns on only when the car is hotter than it should get under any conditions you will find in Marblehead, MA at this time of year. It also turns on with the AC compressor. Its switch to turn on when the car is hot, as opposed to AC, is set at 91/99C from the factory, I think, for low/high speed. Since it is located on the cold side of the radiator, the coolant temp inside the engine would probably be about 230F by the time it went on high. If the cooling system is in good shape, the aux fan very rarely comes on. I don't think it was your problem.

  21. #21
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    Darn it! But your probably correct.
    Only thing I can do is try it out for awhile. Yeah the aux. fan was on for sure.
    I don't mind taking the time for a headgasket change, but just wanted to know
    the "real" problem before tearing it apart.
    Thank you!!!

  22. #22
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    The real problem seems to be you're missing your mechanical fan. Like pbonsalb said the aux fan is for extra cooling while the AC is running and when you REALLY need the help. The mechanical fan (connected to the WP shaft) should handle things 99% of the time, particularly in MA. My aux fan hasn't worked since I bought the car and it's never hinted at overheating.

  23. #23
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    definitely not any fan. when driving, the air from driving is far more than enough to cool the radiator.

  24. #24
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    Well...we both made assumptions. You're assuming he's constantly moving to rule out the fan. I assumed he wasn't moving, or maybe stop and go, since getting the aux fan moving lengthened his running time.

    I'd still like a definite answer to the bleed question. I've done a number of coolant jobs and I still usually need to top up a couple days after with some highway driving. Tough to get a 100% bleed in the driveway.

  25. #25
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    Well...we both made assumptions. You're assuming he's constantly moving to rule out the fan. I assumed he wasn't moving, or maybe stop and go, since getting the aux fan moving lengthened his running time.

    I'd still like a definite answer to the bleed question. I've done a number of coolant jobs and I still usually need to top up a couple days after with some highway driving. Tough to get a 100% bleed in the driveway.

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