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Thread: 88 735i overheating

  1. #1
    Join Date
    Jul 2010
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    Westlake,OH
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    1988 BMW 735I

    88 735i overheating

    Sadly, I have noticed that my 88 735i, is overheating SOMETIMES . Right after I purchased it, I went ahead and ran clean water throughout the cooling system to clean the dirty coolant (the car sat for about 16 years). Well, after several cycles, I have managed to get clean water coming out of the cooling system (I have not fill the system with coolant yet). Problem is that sometimes the engine temperature needle goes toward the red zone suddenly, (now, is not reaching the critical zone ) sits there for about 5 minutes, then comes down to the middle area ( visco fan is not engaging yet ) then goes up a little, visco fan engages, and everything comes back to normal. I have already replaced the thermostat, and I am planning to do the same with the water pump. Before replacing the thermostat and visco fan, temp would go straight to the red zone, and warning signal would pop up on the dash. As I already said, water is still in the cooling system, not coolant. Am I on the right track ?
    Thank you.

  2. #2
    Join Date
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    Boynton Beach, Florida
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    1990 735I (E32) M30
    I would check the resister on the Aux Fan. My 1990 looks like this. Some cars have a ceramic one that looks different. If the Aux fan does not come on and off as it should you can overhead simply sitting at a light.
    1990 735I (Auto) E32 Feb 1990 to Present
    1996 Z3 Roadster (5 Speed) E36/7 Jan 1999 to Dec 1999
    1983 733I (5 Speed) E23 April 1983 to Feb 1990
    https://www.youtube.com/watch?v=2d4tHoHGaJo
    https://1drv.ms/v/s!Av20xCMMocSsyEpl...h_oOk?e=ekIcAT







  3. #3
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    Jul 2016
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    Chicago, Illinois
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    3,842
    My Cars
    are slow
    Car should only need one fan to hold itself in the middle. Bleed

    Red zone is 120C+ jsyk.
    Last edited by XAlt; 08-23-2017 at 10:04 PM.

  4. #4
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    1988 BMW 735I
    I will check the resistor and do another bleeding...
    Thank you guys

  5. #5
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    11/88 E32 750iL+98 E36M3
    bleeding http://www.nmia.com/~dgnrg/page_19.htm
    visco fan, Fan Clutch test
    First, lets discuss what the fan clutch does and why it is there. The fan clutch is just what the name says, it is a mechanism that will clutch the fan on and off depending on the need for more or less cooling air to flow thru the radiator. It is a thermostatically controlled device that when operating normally will vary the fan speed independently of the engine speed. When cruising down the road at freeway speeds, with outside temperature less then desert conditions, the fan should be merely be idling along, turning just fast enough to add a little air flow when needed, in this way the fan noise and drag on the engine is greatly reduced. When reducing speed, the fan clutch will sense higher temperatures thru the radiator and “clutch up” thereby increasing the fan speed to help maintain constant engine temperature. It may in fact, cycle as the temperature of the air thru the radiator changes depending on airflow. If the fan clutch operation is normal, when first starting the car, the fan clutch should “clutch up” and an increase in noise and airflow should be obvious. After about 60-90 seconds, the fan will un-clutch and the noise and airflow will drop. The fan will continue to turn but at a much reduced speed. As the engine warms and the thermostat opens to regulate the temperature, the air thru the radiator gets hotter and the clutch will sense this, thereby increasing the speed of the fan to maintain a normal operating temperature.
    First signs of trouble:
    A normal temperature indication at freeway speeds and an increasing temperature as the vehicle slows is one of the first indications of trouble. Many other things may give this indication but if the temperature seems to be stable at speeds but climbs in traffic or while stopped, this is a good indication that the fan clutch isn’t working correctly. As the temperature continues to climb, the auxiliary electric fan should start but may not provide enough air to keep the engine from overheating.
    Another sign of trouble is if the fan noise is high and never decreases after starting, and is there anytime the engine RPM is higher then idle, this means that the fan clutch is “frozen” and is not releasing. Although this will not result in immediately serious trouble, it will load the engine continually and gas MPG will be reduced. Load on the fan belt(s) will be higher and shorten the life of that component also.
    Fan modifications:
    It has been suggested that other models of BMW fans can be substituted to reduce the noise and load of the fan. This is NOT recommended! If the fan clutch is working properly, there should be no need to replace with a lesser fan. The noise and load of the fan should only be there when it is “clutched up” and the fan speed needed to keep that big V-12 cool. BMW designed it this way and it is never a good idea to alter the cooling system and in particular where alloy engines would be effected.
    Testing the fan clutch:
    If you have reason to suspect that the fan clutch is defective, here is the recommended procedure to verify the condition of the fan clutch.
    1. Start the car (cold) with the hood open and note if the fan is turning, increase the engine RPM and note if the fan turns faster and the noise increases, if it does, first good indication, if it does not increase speed/noise, clutch is bad and needs to be replaced. (Remember, this must be tested after the car has been off for and extended period, over night etc.)
    2. Leave engine running and note if the fan starts to slow down after 2-5 minutes, speed/noise should diminish and even raising the RPM, the fan should not make as much noise as when first starting, if it does slow, this is the second good indication. If speed/noise does not decrease, clutch may be “frozen” and should be replaced.
    3. Leave the engine idle and watch the temperature indicator. When normal operating temperature has been reached, some increase in fan speed/noise should be noted, in particular when the RPM is increased. If temperature is fairly stable and the fan noise/speed increases or cycles, third good indication. If temperature indication continues to increase, with no increase in fan noise/speed, clutch is defective and should be replaced.
    4. After the engine is at normal operating temperature or above, is the only time that the “rolled up newspaper” test that many people talk about should be performed! Take some newspaper and roll it up into a long narrow tube. Be carefull, keep hands and fingers away from the fan while performing this test! With the engine at full operating temperature and idling, take the rolled up paper and insert it on the back side of the fan and try to reach the hub of the fan avoiding the blades until close to the hub. Push the rolled paper at the fan increasing the friction to the hub area of the fan. If the fan can not be stopped easily this is the fourth good indication, if it can be stopped the clutch is defective and should be replaced. Again, this test can only be performed when the engine is at or above full operating temperature.
    Testing can be performed in any order but just make sure the conditions during testing are those that are specified for that specific test.
    Do not continue to operate the engine if the temperature continues to rise and certainly stop if the temperature approaches “redline”.

    Author: Mwrench

    how the visco fan clutch works https://www.bimmerforums.com/forum/s...n-clutch-works

    aux fan: when aircon is on, aux fan runs on low speed always. When aircon is not on, aux fan low speed comes on when a certain temperature is reached, when the next limit is reached, it switched to high fan speed.
    Testing: http://www.nmia.com/~dgnrg/page_20.htm
    If the engine overheats, the temperature switch should automatically run the fan on at low at 196F (91C) and high at 210F (99C). There are also other switches available which switch to hi speed at even lower temperatures.
    Last edited by shogun; 08-23-2017 at 11:57 PM.
    Shogun tricks and tips for the E32 series are HERE!

  6. #6
    Join Date
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    2001 525it
    I remember those engines would start to over heat because the cylinder head gasket between cly 5-6 would degrade

  7. #7
    Join Date
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    1988 BMW 735I
    Thank you all for your inputs. I did check the aux fan with ignition and AC on, and it runs on low speed. I have also jumped the terminals on the radiator temp switch and noticed that the aux fan is running on low when jumping brown and blue, and on high when jumping brown and black : so far I think I can eliminate the resistor, but the culprit becomes the temp switch!!! Am I right?
    Also, When the engine gets hot toward the red line and Visco engages, everything goes back to normal: problem is, the viscous fan does not come on EVERY time when temp goes high: is this Visco fan bad too? This would be the second brand new fan I would have to replace....
    Last edited by jeanro; 08-24-2017 at 08:06 PM.

  8. #8
    Join Date
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    11/88 E32 750iL+98 E36M3
    Basically the visco fan should handle it all, it should run always, the aux fan is just to support the visco when not driving = traffic jam, red lights etc., a good brans visco fan clutch lasts more than 10 years, on my E36 M3 the one is from Behr with a stamp from 1998 and it still works well.
    Make the test as described for the visco fan.
    Testing the fan clutch:
    If you have reason to suspect that the fan clutch is defective, here is the recommended procedure to verify the condition of the fan clutch.
    1. Start the car (cold) with the hood open and note if the fan is turning, increase the engine RPM and note if the fan turns faster and the noise increases, if it does, first good indication, if it does not increase speed/noise, clutch is bad and needs to be replaced. (Remember, this must be tested after the car has been off for and extended period, over night etc.)
    2. Leave engine running and note if the fan starts to slow down after 2-5 minutes, speed/noise should diminish and even raising the RPM, the fan should not make as much noise as when first starting, if it does slow, this is the second good indication. If speed/noise does not decrease, clutch may be “frozen” and should be replaced.
    3. Leave the engine idle and watch the temperature indicator. When normal operating temperature has been reached, some increase in fan speed/noise should be noted, in particular when the RPM is increased. If temperature is fairly stable and the fan noise/speed increases or cycles, third good indication. If temperature indication continues to increase, with no increase in fan noise/speed, clutch is defective and should be replaced.
    4. After the engine is at normal operating temperature or above, is the only time that the “rolled up newspaper” test that many people talk about should be performed! Take some newspaper and roll it up into a long narrow tube. Be carefull, keep hands and fingers away from the fan while performing this test! With the engine at full operating temperature and idling, take the rolled up paper and insert it on the back side of the fan and try to reach the hub of the fan avoiding the blades until close to the hub. Push the rolled paper at the fan increasing the friction to the hub area of the fan. If the fan can not be stopped easily this is the fourth good indication, if it can be stopped the clutch is defective and should be replaced. Again, this test can only be performed when the engine is at or above full operating temperature.
    Testing can be performed in any order but just make sure the conditions during testing are those that are specified for that specific test.

    Sure the impeller on the water pump does not slip?
    Hot at idle would indicate to me: visco clutch, a lack of flow through the radiator like partial blocked radiator, or pump issues. Then as mentioned before: Inability of cooling system to keep up with heat generated by engine = headgasket leak pushing exhaust gas into cooling system. You could make a compression / leak test of the engine.

    example water pump impeller:..... I also pulled the water pump and 2 things: the plastic impeller had separated and the metal surrounding the shaft had broken off and gotten stuck in the block https://www.bimmerforums.com/forum/s...+pump+impeller
    Last edited by shogun; 08-25-2017 at 12:49 AM.
    Shogun tricks and tips for the E32 series are HERE!

  9. #9
    Join Date
    Jul 2010
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    1988 BMW 735I
    Shogun, I really hope the head gasket is OK. How do I perform the compression test you are talking about?

    - - - Updated - - -

    I am also planning to pull out the water pump....

  10. #10
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    11/88 E32 750iL+98 E36M3
    I do hope too, but that is just to check all possibilities to find the problem http://www.bmwe34.net/E34main/Troubl...e_diagnose.htm
    Compression test:
    Each cylinder must produce it's share of power. A lack of sealing in any cylinders will have an effect in the engine power and driveability.
    Procedure:
    1. Remove all the spark plugs, disconnect the DME main relay and fuel pump relay (engine with EML, remove the fuel pump relay). 535i, disconnect the ignition coil wire.
    2. Install the compression gauge in the 1st cylinder, crank the engine a minimum of 4 revolutions and record the first and the highest readings. If the 1st reading is low and slowly increases to a normal reading, worn rings or cylinder walls are likely to be a problem.
    Results: Minimum: 10-11 bar (142-159 Psi) - Maximum difference between cyl: 0.5bar (7Psi)

    • Cylinder leak testing:
    A leakage tester applies regulated compressed air (from a compressor) to a cylinder trough the spark plug hole. A gauge the percentage of air pressure lost from the cylinder.
    Procedure:
    See the website1 for FAQ, website2, website3
    to build your own leakdown tester. The location of the leak can be pinpointed by carefully listening for the air escaping. Leaking exhaust valve will be heard exiting the exhaust, the induction system for the intake valve.
    Air bubble coming out of the coolant system could indicate a faulty headgasket or cracked head.
    Worn piston rings, the air will be heard from the crankcase of the valve cover vent.
    When performing the test, a small percentage of leakage by the cylinder rings is considered normal when the engine is off.

    https://www.howacarworks.com/engine/...mpression-test

    Harborfreight has a kit for $25 which might work. Compression Test Kit 8 Pc , quote: This complete engine compression test kit includes everything you need to check valves and rings, perform carbon buildup inspection and test for late timing on a wide range of vehicles. The kit comes with an extension hose, straight and angled fittings and a rubberized gauge protector.
    •Check valves and rings, perform carbon buildup inspection, and test for late timing
    •Adapters for a wide number of vehicles (straight, angled, M10, M12, M14, M18)
    •3 in. gauge has dual color scale from 0 to 300 PSI
    •Comes with 20 in. extension hose, straight and angled fittings and rubberized gauge protector

    Symptoms of a Blown Head Gasket:
    •Over heating
    •Low Coolant levels
    •Coolant leaking from the engine
    •White smoke from the exhaust
    •Sweet smell while driving

    If a blown head gasket has an internal leak with white smoke and a sweet smell, you can purchase a Combustion Leak Test Kit from your local parts store. The Combustion Leak Test Kit will test your coolant for the presence of exhaust gases, proving there is a breach between your combustion chamber and coolant passages.
    How the tester works copied: Combustion gas, when it enters the cooling system through any leak, accumulates in the air cushion above the radiator coolant level (in sealed coolant systems, this air cushion must be created by lowering the coolant level about an inch and a half). The Leak Tester analyzes this air: The blue fluid turns yellow when CO2 gas is detected in gasoline engines and green in diesel engines. The double-chamber feature of the Leak Tester assures a high level of accuracy. Conventional detection methods often give incorrect readings because alkaline particles present in the air cushion can cause false indications of a combustion leak. Alkaline particles are absorbed by the Leak Tester's first chamber, which acts as a filter, allowing only air and CO2 to reach the second, upper chamber. If the blue fluid in this upper chamber turns yellow or green, it is proof positive that there is a combustion gas (CO2) leak into the coolant.
    head-gasket-blown-test
    https://www.2carpros.com/articles/he...ket-blown-test
    Shogun tricks and tips for the E32 series are HERE!

  11. #11
    Join Date
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    1988 BMW 735I
    Well, I have some updates now....I did perform another bleeding on the cooling system, and from my last posting I've been trying to replicate the overheating issue with...no success. The car idles for long periods of time without any problems!!! I will however go ahead and do a compression test.
    Now, I have another task to perform: after I turn the engine off, messages pop up on the display : "Low engine oil" and "Oil pressure sensor". I did check the oil level, and is perfectly normal....What can I do? What is wrong?
    Thank you

  12. #12
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    Make the easiest checks first.
    Wire connections
    - at the oil pan bottom there is the oil level switch, it has a short cable with plug, often the plug is brittle and no good contact. http://www.realoem.com/bmw/enUS/show...5iL&diagId=11_
    There are TWO engine oil level contacts on the M70 (maybe also on the other engines).

    static contact
    and
    dynamic contact

    In case the oil level is sufficient, the static contact is closed.
    Via the ground signal the check control get's to know that the level is o.k.
    The dynamic contact is open, the control voltage flows against ground.
    In case the oil level goes under the dynamic switch point, a message comes.
    That the oil flowing into the oil pan when engine is switched off does not delete the alarm, the fault is stored with terminal 30.
    It will only be deleted, when the static contact reports a message/signal, that the engine oil is filled up to static level.

    The wires to the static contact are also checked for wire problems by the system of the car. After ignition is switched on, a oil level warning will come. After starting to drive, but latest after 20 seconds this warning will disappear.
    The wires go thru the pipe in engine bay left side on my M70 together with the thick wire from alternator to B+ pole. Right next to the B+ pole is the connector for these wires.
    Another problem is a dirty float inside the level device which is stuck.
    Bentley manual see page 119-3 oil level sensor testing, page 119-4 shows how to make a oil level sensor continuity test.


    -Oil pressure sensor: check the wires going to the sensor, maybe broken. . Bentley manual page 119-3 oil pressure testing.
    Turn ignition switch on, the warning light should light up, remove the connector from oil pressure switch. Light should go out and check control should display oil pressure sensor.
    If light does not go out, the wiring to the switch is most likely grounded somewhere between the switch terminal and the warning light. See 600 electrical system-general for electr. troubleshooting info.

    If the warning light does not light when ignition is on, remove connector from oil pressure switch and use a jumper cable/wire to ground connector terminal to a clean metal surface.
    If the warning light comes on, check the switch. To test the switch, connect an ohmmeter between terminal in switch body and ground. With engine off, there should be continuity. With engine running, oil pressure should open switch and there should be no continuity.

    Get a Bentley Repair manual
    Shogun tricks and tips for the E32 series are HERE!

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