88 735i overheating at idle with ac on

[slowcar88]

noticed that the temp is creeping up to the red when the car is sitting at idle with ac and recirculation on. not very hot today (80 degree F)

not exactly sure what i should fix first

known issues:

• aux fan fuse (ac fan? fuse 25) melts so i just pulled it, thought it would solve my problem
• AC makes random groaning noise sometimes
• Water pump makes water whooshing noises at startup sometimes

[CroughtonE32]

Where your groaning noise is coming from you need to be more specific. There is a resister that goes every once in a while on your Aux fan and without the Aux fan working your temp will definitely rise when you're at idle with the A/C on. Maybe that's why your fuse is blowing. Looks like this.

[slowcar88]

Thank you. I'm leaning towards replacing the aux fan first.

I couldn't isolate the groaning noise as it is quite random, but I can stop it by turning off the ac in the car.

[CroughtonE32]

Might be the fan is fine. This resister is on the fan. You can see it if you look through the grill. Replacing it might save your fan. Easy part to find. Even on Ebay. See if the noise is coming from your compressor. Just because the A/C belt is turning the compressor doesn't mean it's on. The center of the unit has to be spinning. It goes on and off getting it's temperature reading from a little stick plugged into the evaporator. Just near your knee on the driver's side. When you remove the knee panel and see the evaporator you'll see the temp gauge plugged into it.

[shogun]

if the fuse blows, the aux fan is bad, that is caused by the magnets inside the aux fan motor, they get lose = motor goes heavy or gets stuck cpl. and then the fuse melts. http://kharon.suomiforum.com/www/bmw...594_magnet.jpg
Do NOT install a larger fuse, friend of mine had the idea, also lose magnets inside the motor, in the end the cpl. fuse box melted and the wires from aux fan to fuse box were blank wires, all melted.

German text translated with deepl:
The aux fan series resistor should be between 0.5 and one ohm. If you measure a higher resistance, then it is broken. In your case, however, I suspect a defective fan motor. You can do the math: 12 volts and 0.5 ohm series resistor results in a maximum current of 24 amps. That should withstand the 25 A fuse, even if it is borderline. The problem is rather that when the motor is blocked, the internal resistance of the motor drops and the total voltage drop occurs at the series resistor. Again, you can do the math: 12 volts and 0.5 ohms equals 288 watts. The 50 watt series resistor can't take that for long and dies a heat death. So the usual system death for the auxiliary fan should play out as follows:

Variant A: The fan blocks in stage 2: The fuse blows because the blocking motor draws too much current. The system is dead, the series resistor is saved (even if this is of no use anymore).

Variant B: The fan blocks in stage 1: The series resistor gets the whole voltage drop and blows. When stage 2 is requested by the electronics due to insufficient cooling, the fuse blows (like variant A). Result: Fan, series resistor and fuse blown.
So much for the theory... and now the practice

The motor does not block because of defective bearings, but because the magnets loosen from the motor bell housing. The loose magnets then drag and eventually block the motor. This happens because the bonding is a real bodge: the adhesive is applied in strips, i.e. not over the entire surface. Moisture can penetrate. Since the aux fan motor is of open construction and is also installed in a fairly exposed location in the vehicle, it does. Water is the death of any bonding, especially if it also freezes in winter. The whole thing can be repaired though: Bumper off, fan out.

Disassemble the fan. In my case, the 3 studs tore off when I unscrewed the motor (despite rust solvent, just too much rust). But it doesn't matter. Since you disassemble the motor anyway, you can drill out the remains of the bolts and cut thread M5. Then use M5 x 10 bolts when reassembling from the outside. This works fine, but the screws must not be longer, otherwise the motor will be blocked. When you hold the motor in your hand, you will see that the bell is pressed in 6 places. After grinding the pressed areas (Dremel) you can pull the motor apart. This may take some force, since the motor is blocked. Now you will find the loose magnets. Clean the magnets and the surface well and glue them with 2K epoxy (e.g. Uhu Endfest). If, as in my case, a piece of the magnet is broken off, it doesn't matter. Simply leave it out. The motor still has enough power. There is no unbalance because the magnets are glued to the stator: After the glue has cured, the motor can be put back together. Before that, you should take the opportunity to re-lubricate the bearings. Instead of gluing, I simply closed the motor with 6 spot welds. But be careful: Before welding, close all ventilation openings of the motor (the magnets inevitably pull all chips into the motor). Now a test run can be done. Translated with www.DeepL.com/Translator (free version)

Also check the visco fan clutch, maybe that is also at the end, http://www.mwrench.com/Whitepapers/FanClutchtest.pdf

[slowcar88]

thanks shogun. i had come across that data before so figured it would be best to just replace the entire fan. will report back once replaced.

[Timm]

If you are overheating at idle then the auxiliary fan is not your problem - it is there to serve the A/C system, it can save the day in an emergency by running the fan at full speed and it does not need the resistors for that function. Engine cooling is the domain of the viscous-coupled fan and it sounds like either the coolant is not circulating correctly (you need to bleed the system) or the viscous-coupled fan has failed. All explained below (relevant for all models of the E32:

[shogun]

Timm, in this case the aux fan is also a problem, besides other possible problems like visco clutch, he posted:

known issues: aux fan fuse (ac fan? fuse 25) melts

if the fuse melts, something is wrong, turn the visco fan by hand and try if it moves freely. I assume the motor is tuck by lose magnets. There are in total 6 magnets inside the motor, 3 x +, 3 x -

[slowcar88]

So the engine only overheats when AC is on at idle. When ac is off, engine can idle fine. Would this still suggest a different issue vs aux fan? Will look into the main fan

[shogun]

Test the aux fan: http://www.nmia.com/~dgnrg/page_20.htm
First try to move the fan by hand, if it is hard to move, if not free moving, then something is wrong with the magnets in the motor and you need a new aux fan.

when engine only overheats in idle, stop and go, then most probably the visco fan clutch is the problem. See Timm's excellent 13 minutes video, explains it all, also blocked airflow etc,you can also test it as per Mwrench info, link I posted above and copied here:
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.

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 careful, 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”.

[slowcar88]

Thanks! will try this out

[shogun]

after you have checked all that and found no fault, then check the water pump.
M30 overheating, cracked impeller of water pump https://www.bimmerforums.com/forum/s...-of-water-pump

[slowcar88]

here is the fan clutch test. I believe this might be going bad? It took some effort to stop it, but it was stopped.



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 careful, 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”.

[shogun]

if that is at operating temperature, then you have a defective fan clutch, get a new visco fan clutch, not that expensive nowadays

[slowcar88]

thanks shogun!

[slowcar88]

quick update. successfully installed a vdo fan, and thought i solved the problem, but fuse 25 melted again...

engine does not overheat anymore.

here is the part i bought:

https://www.fcpeuro.com/products/bmw...do-64541392913

[shogun]

check the wiring from fuse box fuse 25 . I remember once a friend had a fried aux fan and the fuse 25 melted although he installed a new fan, the old fan had melted the wires of the aux fan system , see page 0671-10
https://shark.armchair.mb.ca/~dave/BMW/e32/e32_88.pdf

maybe blank wires inside the fuse box under fuse 25, you have to test all those wirings related to fuse 25 and 29

http://bmwe32.masscom.net/johan/fuse...ox_restore.htm

[slowcar88]

Update on the situation. New vdo fan worked for about 2 months, now it’s completely dead.

Not sure if it’s a defective part but it’s not running at all at idle with the ac on, which caused the car to overheat after about 1hr at idle on 80degree sunny day.

Fuses seemed fine. Btw, replaced 30amp fuses with older bmw thick plastic/ceramic looking fuses from eBay. The new plastic stuff just melts.

Need to evaluate what to do next. Maybe comeplete new vdo fan, or resistor (but it should be ok because it was a new part…)

[Cactuar]

Did you try to apply battery voltage directly to the fan?

[shogun]

test http://www.nmia.com/~dgnrg/page_20.htm
we had several cases where the fan was ok, but the plug connections to the aux fan directly at the aux fan had no contact, oxidized, same happened with the relays, used contact cleaner and enhancer and the fan worked again. Check systematically with a multimeter how far the power goes, use the wiring diagrams to see the wire routing, from....to.
Ever changed/tested the 2 relays K21, K22 in aux relay box 1? http://www.e32-schrauber.de/bmw/date...8_88-07_94.pdf

[slowcar88]

Thank you both. Will test the connections.

At quick glance, it looks like the plug going into the rad/temp switch is cracking a bit. Does anyone know the part number for the wiring and male plug?

[slowcar88]

Looks like shogun already answered my q above:

61131378410

https://www.bimmerforums.com/forum/s...tch-Pin-Layout

[slowcar88]

i jumped the aux fan and it does not work on high or low. on low, i can hear the relay click, on high, i dont hear anything. would this suggest a bad fan?

also, does anyone know the part numbers for the highlighted relays (k21, k22, k33)?

[shogun]

Make more tests to check the wiring from fuse box to aux fan, as Cactuar already mentioned: Did you try to apply battery voltage directly to the fan? That means directly the pins on the plug at the aux fan. If that works, go 1 step back and test at the place where the wire loom coming from aux fan goes, if you have power there, next step, etc.
As your fuse 25 always melts, I assume you have a wiring problem. check the wiring from fuse box fuse 25 . I remember once a friend had a fried aux fan and the 30A fuse 25 melted although he installed a new fan, the old fan had melted the wires of the aux fan system , see page 0671-10 https://shark.armchair.mb.ca/~dave/BMW/e32/e32_88.pdf The wires of fuse 25 were melted under the fuse socket. Here on the site of Johan you see how he rebuilt his fuse box
http://bmwe32.masscom.net/johan/fuse...ox_restore.htm Before you pull apart the fuse box, measure with your multimeter, step by step so that you find the area where a problem is in the wiring.
Pull out the relays, use contact cleaner, enhancer.
The part numbers for the relays are written in front of the relays, at least the old part numbers with 7 digits, but that will help you to find latest p/n. Check the ETK in section vehicle electric system, there all relays are listed and also the pattern of the pins of the relay, compare that with your relays, http://bmwfans.info/parts-catalog/E3...arious_relays/
or tell us what is exactly written on these relays in your car, then we can help you to find the correct part numbers.
But first you have to test with a multimeter all the wirings of the auxiliary fan system, if fuse 25 always melts even after you installed a new aux fan, there is a wiring problem, I assume there is a blank wire somewhere, melted.
Track down the cause of a short circuit that melted wires.
How to check if there is a break in a wire using a multimeter https://www.premiermot.co.uk/2016/09...-a-multimeter/

[shogun]

any update available?