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Thread: e34 overheating

  1. #1
    Join Date
    Jul 2004
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    California, USA
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    34
    My Cars
    92 BMW 525i

    e34 overheating

    I am running out of ideas. My e34 is overheating and i am not sure why. So far I have replaced the radiator, water pump, thermostat, fan clutch, and its still overheating while its idle on the freeway. I seriously cant think of another reasone for it overheating. If anyone has any idea as to a possible problem, I would greatly appreciate the suggestion. I am seriously running out of possibilities. Thanks for your time.
    "If we don't succeed, we run the risk of failure."
    -President Bush


    1992 BMW 525i wishing for an M5...

  2. #2
    Join Date
    Jul 2002
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    '04 M3/MT Coupe,'04 X3
    There's probably nothing seriously wrong with your car, but since you've replaced most of the cooling system, there's a good chance that you just have some air in there.

    E34 525's are a pain to bleed. www.bmwe34.net is down right now, otherwise they have a good page and procedure.

    In a nutshell, keep bleeding air out of the bleed screw on the radiator. You'll want to run the heater some to try and get all the air out of the heater core. Also "massage" the radiator hoses to make sure there aren't any bubbles hung up in there. Massage seems to be the popular word for that, it just feels weird telling anyone to massage a part of their car.

    There's the chance that you could have some buildup and crap in the motor, in which case you'd have to flush the hell out of it and see if it improves.

    Beyond that, I have no idea.

    Good luck!
    -Aaron
    2004 M3 - Coupe, 6spd, Silver Grey on Black
    | RAC RG63, PSS, ZCP Brakes, aFe, SS (V1, Res. X-pipe, Street Muffler), Epic Alpha-N, 319whp |
    2006 Jetta TDI/DSG, Pkg 2, Silver on Black - Sold
    2004 M3 SMG - Silver Grey on Black, Convertible - RIP
    1995 525I 5spd - Black on Black -Sold
    2004 X3 3.0i AT- Blue on Tan - For the wife....

  3. #3
    Join Date
    May 2004
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    90' 525, 95' 525, 98' 528, 97' 540
    After I replaced my cooling system parts, hoses and gaskets, I had this problem too. What I was told to do by a mechanic was to drive for about 2 minutes not letting the RPM fall below 3k. This gets the water pump really moving and gets everything goin... then step out of the car, open the bleed screw, let the air come out ... close the screw when the coolant starts flowing. And if it still overheats repeat the procedure. I only had to do it twice and it's been working like a charm ever since!

    Hopefully its something small like that.. good luck to you

  4. #4
    Join Date
    Jul 2004
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    California, USA
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    My Cars
    92 BMW 525i

    thanks

    Thanks guys! I found a small leak in the heater control valve so i replaced that hoping that that was the problem, and it got better but still has the problem. Thanks for the advice though, ill try that. Just saddening seeing that needle move from the half way mark toward the 3/4 mark. Ill test out your suggestions tommorow.
    "If we don't succeed, we run the risk of failure."
    -President Bush


    1992 BMW 525i wishing for an M5...

  5. #5
    Join Date
    Nov 2002
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    SATX & DC
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    '11 535iX
    I am having the same problem with my 735i. I have replaced the fan clutch, thermostat, aux fan switch, flushed system at least 4 times, bled numerous times...and all seems fine around town and even on a 200mi road trip.

    Until, until after I take the road trip, then my car overheats within 2mi of driving after having sat overnight. This has happened twice now.

    I am being to wonder if I have a headgasket problem whereby gases are entering the cooling system.

    Anyone have any ideas?
    300E
    Audi A6
    F250 Powerstroke
    325es
    735i

  6. #6
    Join Date
    Jul 2004
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    Yorktown, VA
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    1989 535i 5-speed
    Hey Crosbo, on your car there is a hose running up the left side of your fender to the coolant tank at the firewall (I'm assuming you have an e32). With your engine cold, start it up with the cap off. As the thermostat starts to open, coolant should begin to pee out of the small hole into the tank. If it's clogged, the old M30 will start to overheat. The hole is only about 1/16", so I opened mine up to about 1/8" and ran a long piece of weedeater line all the way through to the front. Haven't had a problem since. It's worth a shot, good luck.

    Sorry rawlz, I don't know the 2.5L engines that well to help you out.
    1989 535i 5-Speed--Lachssilber Metallic--e39 17" Staggered Style 32 wheels--Kumho Ecsta SPT--Raybestos QS Ceramic--Jim C chip--UUC Short Shift--Sachs Sport Clutch--Racing Dynamics Springs & Swaybars--Bilstein Sports--Mason Engineering Strut Brace--3.46 Limited Slip--19 lbs/hr Mustang D5B Injectors--3.5 bar Porsche 944S FPR--Bosch Euro DE Headlights--Yorktown, VA

  7. #7
    Join Date
    Oct 2002
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    bay area, CA
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    91 M5
    does it overheat while just idling on your driveway?
    when it starts to get "hot", touch your hoses (especially the upper hose) and radiator - are they getting warm/hot too? if not, double check thermostat function AND direction. and maybe water pump and fan belt.

    is the sensor/sending unit ok?

    does turning on the heater and fan full blast lower the temp at all?

  8. #8
    Join Date
    Nov 2002
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    '11 535iX
    It doesn't overheat all the time. Only after what seems to be the day after a long trip (200mi).

    All the hoses get pretty hot and the aux fan does not kick on...I believe because water is not touching the recently replaced sensor. I have tested the fan and it works at both speeds.

    I followed another's advice and pulled the small return hose from the radiator, then attempted to blow thru to the reservoir...extremely difficult (yes the cap was off). The restriction seemed to be the filler neck or nipple, so I did my best at trying to open/enlarge the passage. Then re-bled the system.

    So far today, runs great with no temperature fluctations. Doesn't even get warm enough for aux fan to kick in. However, this is what happened last time...ran fine, even on the 200mi trip, until the day after when it overheated on a 2mi drive...from what appeared to be a system full of air, but once bled down, the coolant level returned to normal.

    Further thoughts?
    300E
    Audi A6
    F250 Powerstroke
    325es
    735i

  9. #9
    Join Date
    Oct 2002
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    bay area, CA
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    91 M5
    1) if you can't clean out a restricted return hose, replace it (cheap).

    2) don't like to hear you say system is full of air. re-try bleeding techniques, make sure heater is on to full hot. on another bimmer, someone had suggested bleeding while car is either uphill or facing downhill - forgot which

    3) one trick from old days is to drill a little hole eg 3/32th in the thermostat in the outer perimeter (not the part that opens and closes). this may help release trapped air.

    4) if you really find a buildup of air, bring your car to a radiator shop and have them check the coolant for exhaust gases - from head gasket leak

  10. #10
    Join Date
    Nov 2002
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    SATX & DC
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    '11 535iX
    Thanx Mywong.

    Well, the car has driven around town all week long with the AC running, without a hitch. I have even sat in parking lots with the AC on and running for 20-30min at a time without a problem.

    However, I was not pleased with my last attempts to fully create a freeflowing scenario thru the return nipple on the reservoir tank. So, I purchased a long 1/8" drill bit and drilled the nipple clear for an restricted passage.

    After thoroughly bleeding, I checked the hose temps. The upper radiator hose heated up but the lower hose remained cool to the touch for quite sometime, even after the vehicle reached operating temperature.

    Should the lower hose be alot cooler than the upper?
    300E
    Audi A6
    F250 Powerstroke
    325es
    735i

  11. #11
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    Oct 2002
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    bay area, CA
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    91 M5
    a hot upper hose shows hot coolant exiting from the engine is passing thru a thermostat that has opened (it cannot tell iwhether the thermostat opened completely or not) .

    the lower hose is cooler by design as the it carries coolant than has been now cooled by passing thru the radiator.

  12. #12
    Join Date
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    Ah great, then that is some good news.

    I went out and hit the hwy for 70-85mph for about 30mi, then returned and parked the car for a couple of hours to cool. I then attempted to bleed the system and got fluid immediately.

    So, I am hoping after having replaced everything but the waterpump and headgasket, I am okay. Another 500 mi round trip coming up in a week or so, guess we'll see.

    Thanx for your assistance.

    --tom
    300E
    Audi A6
    F250 Powerstroke
    325es
    735i

  13. #13
    Join Date
    Jul 2003
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    Austin tx
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    89 525

    Thumbs up

    All i have to say is that Bfc rocks!!!!!!!!
    By following the instructions on this page i was able to get my overheating gremlin done before i bought a pump thermostat or God forbid a radiator!!!!.
    Did i mention Bfc ROCKS?????
    IT DOES!!!!!!
    Size Does Matter!!!

  14. #14
    Join Date
    Feb 2019
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    Blackfoot
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    1995 bmw 525i e34
    I have a 1995 bmw 525i e34 that has been overheating as well I replaced the thermostat and the thermostat housing then I replaced the water pump and the heater still won’t work and still overheats I’m running out of ideas of what it could be any ideas?

  15. #15
    Join Date
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    Ann Arbor, Michigan
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    1995 BMW 525i 5 speed
    Could be air in the system. Try bleeding it. I raise the nose up about six inches to help the air to escape. Also while bleeding make sure the heat is on full. Good luck. Cheers. George

  16. #16
    Join Date
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    hiss by my window
    Quote Originally Posted by MissCK View Post
    I have a 1995 bmw 525i e34 that has been overheating as well I replaced the thermostat and the thermostat housing then I replaced the water pump and the heater still won’t work and still overheats I’m running out of ideas of what it could be any ideas?
    The lack of heat at the heater indicates either no flow(very unlikely with new pump) of gasses in the cooling system. Gas could be air if not completely purged after the service or, more likely given your history of over heating, a failed head gasket which is allowing combustion gasses into the cooling system.
    Sorry for the bad news.

    If you can leave two black stripes from the exit of one corner to the braking zone of the next, you have enough horsepower. - Mark Donohue

  17. #17
    Join Date
    Jan 2019
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    525
    Open the radiator cap, fill up to the brim, and run the engine at idle. Watch. If you see a steady stream of small bubbles appearing, then hold the throttle down slightly - if the steam increases in quantity, then very likely you have a breach in the coolant jacket in the cylinder head.

  18. #18
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    Quote Originally Posted by chislern View Post
    Could be air in the system. Try bleeding it. I raise the nose up about six inches to help the air to escape. Also while bleeding make sure the heat is on full. Good luck. Cheers. George
    I see this everywhere, the idea that the front of the car needs to be jacked up or the car needs to be parked on an incline to permit proper bleeding. It does not. Bleed normally cold and then with the engine running at idle, with cabin heat activated always. then go for a drive during the day with cabin heat activated (blower need not be). Then the next day, open the cap and topup coolant to the brim. You're done. That's it and that's what's in the Bentley manual. Have done this for nearly ten years with no problems.

    The engine is inclined towards the front. The cylinder head has a bypass cavity going straight to the upper radiator hose. This together with the agitation that comes from the pump during driving, will drive air bubbles out of the engine, and to the radiator, where they are purged by coolant drawn down and into the engine from the expansion tank. This is why the day after a bleed and drive you may have to even top up half an expansion tank's worth of coolant - that much air has been naturally purged out to the radiator by the cooling system.

    If you have half a tank to top up the next day, drive for another 2 days and check and topup again. Half a tank is not very usual - more like up to a quarter.

  19. #19
    Join Date
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    If the water pump and thermostat were installed correctly, then I agree it sounds like the system hasn't been bled properly. The pressurized expansion tanks in these cars are NOT like simple overflow tanks. You need to loosen/remove the bleed screw (I do it with engine running from cold, adding coolant as necessary), until all the air comes out, until the air bubbles stop, and just coolant comes out.

    I started this thread to help explain what's going on in these cooling systems:
    https://www.bimmerforums.com/forum/s...ding-Explained

  20. #20
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    1995 BMW 525i 5 speed
    I raise the nose for added insurance. Doesn’t take long and adds to my peace of mind.

  21. #21
    Join Date
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    Elevate the nose (on a steep driveway, etc.) so the bleed screws is on the horizontal plane of the coolant reservoir level indicator, open the cabin heat to full blast, warm the car to normal operating temperature so the thermostat opens, then open the bleed screw and let the bubbles out until the coolant runs clear. Repeatedly squeezing the upper radiator hose helps flush out the air faster.

    Monitor the temperature and coolant level again every few drives, in case air is getting in when the car cools and the now lower internal pressure sucks air in past leaky hose clamps, etc.

  22. #22
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    Quote Originally Posted by chislern View Post
    I raise the nose for added insurance. Doesn’t take long and adds to my peace of mind.
    The insurance you require is just topping up coolant levels the next day after driving in between with the heater controls activated. Most people don't do this (activating heat but not blower during a cold bleed which is in the instructions) which is why they don't get heat and wonder what's wrong. Elevating the nose or parking on an incline is not the least bit necessary and yet is often recommended online as if essential to the task.

  23. #23
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    Doesn’t hurt anything to raise the nose. I’m the original owner of my 1995 525i and have done it this way for many years with good results. Just my take. To each their own opinion. Cheers!!

  24. #24
    Join Date
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    Quote Originally Posted by Thomas525 View Post
    The insurance you require is just topping up coolant levels the next day after driving in between with the heater controls activated. Most people don't do this (activating heat but not blower during a cold bleed which is in the instructions) which is why they don't get heat and wonder what's wrong. Elevating the nose or parking on an incline is not the least bit necessary and yet is often recommended online as if essential to the task.
    If elevation of the nose is not required, why do any of my several M30 engines flow clear and non-bubbled coolant only when nose-elevated, but not when on level ground? Otherwise, how would the air that collects in the head escape?

  25. #25
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    My take: Raising the nose can't hurt, and sure, in some cars it will help get all the air out of the rest of the system where it can be release from the bleed screw or forced into the expansion tank.

    But it also isn't necessary. A little air in the rest of the system will promptly get forced into the radiator through normal driving. These systems are somewhat self-bleeding, with repeated hot and cold cycles, so excess air will eventually make it to the expansion tank. That's why checking the coolant level later, when cold, is always a good idea.

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