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Thread: 1994 e36 325i convertible overheating

  1. #1
    Join Date
    Apr 2004
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    NY
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    94 325 CONVERT

    1994 e36 325i convertible overheating

    hi guys, i have a 94 e36 325 that is giving my an overheating problem.

    i have shut the car down quickly when the guage had gotten into the red zone.

    i pulled the water pump out to replace it, and found that i have the plastic impeller.

    the impeller was broken into two large pieces, and some other fragments.

    after installing the new metal impeller water pump, and bleeding out the air a few times, the water temp rises to the the halfway mark on the guage, and stays there for a while (10 minutes or so) then starts to creep up to the red zone again.


    on other posts, i have read people mentioning the head gasket, but
    i do not see any oil in the water, or water in the oil.

    also, i have read, that a 94 shouldnt have an aluminum head, and it is less likely to warp.

    i was not able to find all the fragments of the plastic impeller.
    i tried flushing them out with water, but nothing came out.

    since these plastic impeller pumps are a common problem, does anybody know where these pieces usually end up?
    i am concerned that they are possibly blocking something somewhere.

    also i have been looking for a collant flow chart, but havnt found one for the M50 engine

    this is my only car, and i need to fix this asap to go back and forth to work.

    any help will be very appreciated.

    if i left any info out, just let me know, and ill add it.. thanks in advance.sparky

  2. #2
    Join Date
    Jun 2009
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    South Carolina
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    2004 330 vert 2004 X5
    You definately have an aluminum head. All e36's have them. I think you possibly read somewhere that you don't have an aluminum "block" and that is correct.

    Have you tried driving the car? Here are the symptoms you're looking for....

    Overheats at idle but not highway = bad tstat or bad clutch fan. Most likely the clutch fan.
    Overheats at highway but not at idle = bad water pump
    Overheats at all times = bad tstat.

    All those assume you have all the air out of the system. Tstat's are cheap. Swap yours out. One thing you can try is with the car at idle watch the temp guage. As soon as it even looks like its startting to climb past the half way mark turn on the A/C and see if it drops down. If it does then that is one more vote for a bad clutch fan.

  3. #3
    Join Date
    Apr 2004
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    NY
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    94 325 CONVERT
    hi fly, thanks for the quick response.

    as to your suggestions:

    Overheats at idle but not highway = bad tstat or bad clutch fan. Most likely the clutch fan. --- havnt taken it on the highway due to fear of getting stuck on highway, but have driven it around on side streets, and the temp gets too high.

    Overheats at highway but not at idle = bad water pump --- water pump was JUST changed assuming that it is in propper working order for a brand new BOSCH pump, i dont think its the water pump.

    Overheats at all times = bad tstat. --- still not sure, ill let it idle longer, and try the a/c electric fan to see if that helps.


    i may pull off the thermostat housing to look for pieces jamming the tstat.

    any ideas where they could be hiding?/thanks....sparky

    - - - Updated - - -

    ok, just did a test.
    the weather here in NY is 79 degrees.

    my car was already warm from my previous test.

    i let the car idle.

    starting with the warm car, the temp guage stayed at the half way mark for 17 minutes, then started to climb past half. i turned on the a/c fan, and it still kept climbing. after about 5 additional minutes, i stopped the test when it reached 3/4 on the temp guage.

    the car was sationary throughout the entire test, and i did not rev the engine.....sparky

  4. #4
    Join Date
    Jan 2013
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    Illinois
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    E36
    You probably need a new fan clutch.
    Last edited by Type1Kicks; 06-29-2013 at 08:32 PM.

  5. #5
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    94 325 CONVERT
    type1, do you think this is just coincidence?. i am pretty concerned about the missing impeller pieces blocking the flow...sparky

  6. #6
    Join Date
    Oct 2012
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    danvers ma
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    1994 bmw 318i
    I have found in almost all cases over overheating after any work has been done to the cooling system on these car's is air in the system. Air can become trapped in the heater core and cause an air pocket to cause overheating issues. The way that I usually go about it is bleed the system then take it for a short ride then re- bleed it again with the car at operating temp, these can be stubborn to bleed due to the heater core being the highest point of the cooling system so if you think you have bleed it correct you may want to do it again.

  7. #7
    Join Date
    Mar 2004
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    Brooklyn
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    97 M3, 65 Mustang FB
    Quote Originally Posted by SPARKY70 View Post



    also, i have read, that a 94 shouldnt have an aluminum head, and it is less likely to warp.
    It definitely has an aluminum head and it definitely will not only warp, it will crack.

  8. #8
    Join Date
    May 2013
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    IL
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    1996 BMW 328i
    I agree (for the second time today) with Motorcycle Junk. After you've filled the system with the bleed screw cracked to bleed all the air that you can out of the system, take it for a short drive, like to the end of the block and back. Park the car, and while still running, crack the bleed screw to bleed more air out. I did this 3-4 times and I was fine. Then again, at the same time I did the fan clutch...

    I had an issue where my engine would stay at normal temp for about 15 minutes then start to overheat. What's happening? There isn't enough airflow through the radiator and the coolant slowly starts to creep up to over 212 degrees F. I'm not too sure where 212 is on the factory temperature gauge, but I don't think it's too far from normal operating temp (I could be wrong here though). However, when this starts to happen, the water starts to boil and you don't even notice because the temperature gauge isn't pegged. What happens then? Coolant starts to find its' way out of the engine at the point of least resistance because of the expansion from boiling. I assume that at a certain point coolant is starting to reverse flow through your reservoir tank, reservoir cap, or bleed screw? When this happens, you lose all of your coolant and engine temperature rises even more. I replaced everything in my cooling system (minus the fan(s)) when I had this issue without thinking far enough for the fan clutch to be a possibility for coolant reverse flowing. Your problem sounds eerily similar to mine. Before you commit to buying one though, stick a rolled up newspaper in the engine fan (NOT THE AUX FAN) and see if it can stop it. My old clutch stopped VERY easily with this test. The new fan clutch might rip the newspaper in half. Huge difference. (Note: Do NOT stick your fingers in it, use a rolled up newspaper/magazine).
    Last edited by ecs87; 07-01-2013 at 11:21 AM.

  9. #9
    Join Date
    Oct 2012
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    washington, dc
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    96 E36 Vert 03 E39 M5
    Are you losing any coolant? Any coolant loss and you potentially have a cracked head or bad head gasket. Its pretty common once these cars overheat to damage the HG between 3-4 or 4-5

    Is it 'steaming' out of the exhaust?
    Try the rolled up Newspaper in the clutch fan, : Starting with a cold motor, the newspaper should easily stop the clutch fan, but once the temps increase, and the 'bi-metal' spring in the clutch fan starts to engage, the fan will turn very strongly and overcome the newspaper. Bad clutch will never overcome the newspaper and once warmed up can be stopped by the paper. A locked clutch never stops (and on a cold motor will overcome the newspaper).

    So if you're 'not' steaming, and you are 'not' losing coolant, and your clutch fan behaves properly, you may want to remove and replace the thermostat and thermostat housing. You may find pieces of old waterpump behind that. I use a 82 or 88c thermostat.

    If you make it this far, refill your system, elevate the front of the car about 8-12 inches (I would drive it up on ramps.), and refill this way
    - -a: Open the bleeder screw and remove the radiator cap
    - -b: Key to the 'on' position, heat controls set to full hot and full blast. (Well the fan only needs to be up a few notches, but the temps should be full hot '91'degrees etc)
    - -c: Fill the Top hose on the radiator (driver side) .. Once its full reinstall the hose and tighten clamp
    - -d: Fill the expansion tank and continue filling until no more bubbles flow from the bleeder screw [I recommend using a wide funnel, if you can find a piece of radiator or rubber hose that will slip over or inside the radiator neck, use this as a 'gasket' to help seal the funnel] I find the bubbles are forced out faster if you can get the level of coolant in the funnel higher than the top of the radiator.
    - -e: Once your 'bubbles are gone' start the car (idle). Continue to fill until there are 'no more bubbles'
    - -f: Once the 'bubbles are gone' close the bleeder screw, put the radiator cap on the radiator. Let the car idle (about 15 minutes) until its up to normal temp. Confirm you have heat.
    - -g: Shut car down, let it sit over night to cool. Confirm the coolant level is at the Kalt line. If it is low fill until it is at the Kalt line. (now before you remove the radiator cap after it is cooling, squeeze the radiator hoses.. They should be flexible and not 'hard'. When you remove the radiator cap, listen for a hissing sound. If you hear a hissing pressurized sound it should be very slight.
    - -h: test drive the car after checking the coolant level. It should warm up but not go over 11:59 (a hair before straight up on the gauge). If it starts to over heat, park it, get a combustion gas / coolant chemical test. You are checking for hydrocarbons in the coolant. This is the best check for a bad head or head gasket.

  10. #10
    Join Date
    Apr 2004
    Location
    NY
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    94 325 CONVERT
    Hi guys, thanks for all your help. I bled the system several times, so I pulled the thermostat housing, didn't find any pieces, but replaced the thermostat.

    That seams to have fixed my overheating.

    If anyone else has to do a thermostat, the o ring gasket is easy to get, but the "profile" gasket, seems to not be stocked at auto parts stores, and takes a few days to get. BMW should have it stocked, but since they were closed on Sunday, this turned into a 2 day job.

    Thanks again. Sparky
    Last edited by SPARKY70; 07-05-2013 at 02:07 AM.

  11. #11
    Join Date
    Oct 2012
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    96 E36 Vert 03 E39 M5
    Replacement factory style (plastic) thermostat gaskets for E36 equiped M52 motors come with the profile gasket pre-installed. I dont think its intended to be reused, however ive found putting a bead of semi-hardening gasket sealant on the outside of that gasket helps out. Glad you fixed the issue, once they are running right M52's are pretty tough.

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