This section contains special information on cooling that is not found in the Service or the Bentley manuals.

All information contained in this FAQ is provided by BMW enthusiasts who are not typically fully trained in the art of BMW maintenance. As such, all information in this FAQ is provided "as-is". Any use of this information is strictly the responsibility of the using party. The supplier of the information and the Webmeister assume no liability for incorrect information or use of this information.


82 Degree Auxillary Fan Temp Switch


E24 Aux. Cooling Fan

E24 Cooling System Tips / Upgrades - ALERT

Running Hot? Clean Your Radiator

Cooling System Servicing - More Tips

Windshield Washer Tank Level Sensor Repair

Viscous Coupling Test

Radiator Nipple Repair

82 Degree Auxillary Fan Temp Switch -

BMP sells an 82 degree blue temp switch to kick in the low speed auxillary fan 2 degrees cooler than the current low speed white switch . By switching out the current high speed switch (red), putting the white one in its place and install the blue one where the white one was you effectively lower the temperature at which the low and high speed circuits cut in. This will definitely help the 6-series which, because of it's low hood profile, has a tendancy to run warmer in the summer.

You have to file down the contacts on the white switch to accept the narrower, high speed circuit connectors. BMP can be contacted at 800-648-7278.

Coolant / Anti-freeze

The following was extracted from a VW Quattro FAQ at address:

There is some interesting info here but use it at your own risk....

Recommended coolant/anti-freeze

Autobahn ZVW-237-104 antifreeze & summer coolant. Phosphate free formula for use in Volkswagen & Audi water cooled vehicles Ethylene Glycol based, Phosphate free

Recommended mixture:

Not less than 40 percent coolant, not more than 60 percent. Sold at VW dealers only. Manufactured by BASF Questions? Call 1-800-669-2273

BASF Customer Service: 1-800-445-4134

BASF Marketing Service: 1-800-367-9865

BASF Technical Service: 1-800-521-9100

Info from Marketing Service:

BASF makes a 'generic' brand of GUARANTEED Phosphate Free coolant called ZEREX EXTREME 450. It has been approved by VW, BMW, MB, Audi, Saab, and Volvo. It is also GUARANTEED for four (4) years and 50,000 miles. They said you CANNOT mix this with any other coolant; you must flush the system and fill with the new coolant/water mix.

Info from Tech Svc:

BASF makes two (2) european formula coolants. One is sold by VW, Audi, and Mercedes Dealers. The other is sold by BMW, Saab, and Volvo dealers. The reason for the phosphate free formula is basically two-fold:

(1) Cosmetics: Hard water reacts with phosphates in coolant to form scale deposits in overflow bottles. These deposits could form in other parts of the cooling system, causing blockage and overheating (see next part).

(2) Corrosion: Phosphates tend to aggravate any corrosion that might already be present with any aluminum parts in the cooling system. Aluminum Phosphate is formed, which is insoluble in the ethylene glycol solution of the coolant. The aluminum phosphate will tend to settle out in the cooler areas of the cooling system, causing blockage. This can cause overheating of the engine, which will accelerate the aluminum corrosion. In other words, the corrosion will tend to feed on itself until damage is done to the engine or the coolant is replaced (refreshing the inhibitors).

Engine coolant should be REPLACED every two (2) years to refresh the silicates and other corrosion inhibitors contained in the coolant.


E24 Aux. Cooling Fan - Mike Gordon <>

If your car tends to run hot when stopped in traffic, and has poor A/C performance on hot days, your auxiliary cooling fan may not be working.

The E24 uses a two-speed auxiliary cooling fan. There are two-temperature switches that operate at 91 and 99 degree Centigrade, for low and high speed fan operation, respectively. These may be two separate switches or on later E24, a combined two-temperature switch. These switch(s) are located on the radiator.

You can test the operation of your fan, by switching the key to IGN position and unplug the temperature switch and jumper the connector. You should hear a relay click and the fan start whirring. If your car has the combined temperature switch (3 prong style), unplug the connector from the temperature switch and jumper the 12V common socket(located on the round edge of the connector) to either of the other two remaining sockets (on the flat edge of the connector).

The low temp switch turns the K1 relay which is fused by fuse #3 (15A)and a ballast resistor, which is mounted on the fan housing, reduces the voltage for low speed operation. This resistor dissipates a great deal of heat and as a result it burns out periodically. The part # is: 17 401 373 177 and it costs about $20. It is possible to find a 0.6 ohm resistor that can dissipate enough heat, but IMHO this is not cost-effective as the resistor will cost over $10 and you will need to make amount for it. Remove both kidney grills to replace to the ballast resistor.

The high temp switch activates the K6 relay and is fused with fuse #18(30A).

Two-speed fan operation, you sneer? Sounds like a case of Teutonic Overkill. Why not forget about fixing the ballast resistor and just run the fan at high speed? The car will run a little hotter and A/C performance on a hot day will suffer too. There is a large inrush of current when going from off to high speed directly and the high speed fuse may blow, leaving you with no auxiliary cooling fan. This was the case in my car, which had a blown #18 fuse and a toasted ballast resistor. Lastly, this is hard on the fan bearings, shorting the life of this expensive fan (P/N 17 40 1 362 096 - about $330).

E24 Cooling System Tips / Upgrades-

I'm presently going thru the cooling system of my 1981 US spec 633, chasing down a problem relating to the engine running hot at idle (between the 2/3 and 3/4 marks on the cockpit gauge) and returning to a normal range at speed (between 1/3 and 1/2 gauge indication). More or less the typical fan clutch failure symptoms. However, during the course of trouble shooting and component replacements, I am trying a few things out and learning a few things. To date, I have done the following:

1. Tried a used, but servicable fan clutch. Observation - don't bother trying this - it didn't solve the problem and ended up with me buying a new one anyway as the used one became very stiff. The only real benefit one can note, when the unit fails and or seizes up, it is turning all a the time. As you probably already know, the intent is for the fan clutch to lock up at idle and pull air thru the radiator. Thus, the unit in my coupe was "locked" and pulling air both at idle and at speed. Either way, this hasn't helped me with the problem of temperature "spiking" when idling in traffic.

2. The early coupes use a brass radiator rather than the combination aluminum/plastic radiators of the newer cars and, in the early coupes, the core is a 2 row core. I had mine re-cored by a local shop using a high efficiency, 3 row core. The 3 row core will fit the end tanks and clear the fan clutch/fan with no problem. I attempted to have a drain petcock installed, but there isn't enough clearance under the radiator tanks (either left or right) to do this.

2a. When draining the radiator for removal or annual flush, if you can remove the temperature sensor from the lower right elbow, you can drain most of the antifreeze prior to removing the hose. This is a sometimes "neater" option than just pulling the hose and having antifreeze gushing out and all over the garage floor/driveway.

3. My coupe uses the 2 speed thermal switch (for the aux fan that is in front of the radiator) which sells for about 95 to 100 dollars. You can replace it with the single speed switch, your choice of temperature settings, 82 degree, 89 or 91 degree for the low speed fan or the 99 degree switch for the high speed fan. These switches sell for 15 to 25 dollars each, so for those on a budget, these could be viable options.

3a. I have opted to use the lower speed switch and have wired in a manual switch to activate the high speed circuit of the aux fan. A pretty simple matter of running 2 wires from a switch to the wires at the thermal switch and choosing the speed circuit desired (large spades = low speed circuit, small spades = high speed circuit).

3b. If one wanted to use the original, 2 speed aux fan switch, a manual switch can still be wired in to override the temperature controlled activation. This way, the fan can be toggled on manually or allowed to activate automatically via the temperature controlled switch.

4. Water pumps. I have a part number for a factory, larger impeller water pump that can be retrofitted to all 2.8, 3.0 and 3.3 liter engines. P/N 11-51-1-707-414 has a larger impeller and, I believe is common on the 3.5 liter engines. This information comes from Kenneth Inn, a digest and Roundel contributor.

5. Thermostats. I've learned to not trust the temperature marking on them. Check all thermostats out in a pan of hot water to verify that they open and if you have a thermometer, at what temperature.

ALERT - 5a. - Thermostat housings - there is an upgraded part for the unit that attaches to the block and has the various sensors and hoses attached to it. It's part number is 11-53-1-710-959. The superceded part is no longer available. If you change this part, you MUST change the thermostat and the o-ring. The new thermostat part number is 11-53-1-265-084 and the o-ring is 11-53-1-722-690. If you use the new unit and an old thermostat, the thermostat will be prevented from opening fully and will result in an "running hot" symptom.

Running Hot? Clean Your Radiator - "Gene M." <>

Those of you who are running on the hot side might also want to pull your radiator (easy to do) the next time you are changing coolant or hoses and give it a thorough exterior cleaning. The fins on these radiators are very close together and cannot be adequately cleaned by spraying through them while in the car. You need to get a fine, long bristle brush (a broom with plastic bristles with a feathered ends also works) and push the bristles all the way through the fins with some type of grease cutting detergent. If you look through the fins before cleaning it will look like there is only some fine dust particle--but it is surprising at how much stuff is caught in there (a lot of gnats in central Calif) that won't come out without the brush. The local BMW dealer service guy told me about this procedures. I was able to bring my temp gauge down from above mid point to below mid point in the 100+ heat of California.

Tips on Cooling System Servicing - "Dale B. Phelps" <>

There are several important, safety aspects to servicing your cooling system on big sixes, as follows :

1) the drain screw in the radiator,the drain plug in the block, and the bleeder screw in the thermostat housing all can tend to clog during normal use (the drain in the radiator is least likely of the three.)

2) What this means is that prior to bringing coolant up to operating temperature you should remove the screw/plug and probe the orifice with an appropriate-sized rigid wire. Coat hanger wire is good size for the plug in the side of the block, small dia bailing wire is good for the t-stat bleeder.


***also...KEEP YOUR FACE AWAY FROM THE BLOCK IF YOU ARE DOING THE BLOCK DRAIN PLUG...coolant and debris WILL come rushing outta the hole when you break through to the water journals...ick on you if your face is there...

3) Replace the respective plugs/screws and proceed with your coolant service as you had planned before you started reading this...

Windshield Washer Tank Level Sensor Repair - "Legros, Phil" <>

The level sensor works through a magnetic ring in the float triggering a reed switch inside the stalk of the level sensor. If the connection to the reed switch corrodes through because moisture has got into the unit or the switch itself goes AWOL, the level sensor will either indicate empty at all times (open circuited) or full at all times (switch staying closed even when the float (magnet) moves down with falling water level. The same principle may also apply to the coolant level sensors - haven't checked this out. Repair is simple. Typing this up took longer than fixing mine with new reed switch.


Lift the unit off the washer tank. Close inspection of the cap of the unit shows an inner central piece (with the spade clip lugs on it) that is "clipped" into the cap that fits the tank. Wriggling the spade lug mounting relative to the cap lets you see where the two bits are joined. It is retained in place by a circular lip formed in the plastic cap which can be eased back with a small screwdriver. The plastic is relatively stiff and may break out a small piece. Don't worry it can be sealed up later. When the retaining lip is lifted slightly the inner piece can be levered out (mine flicked out and flew across the workshop!!) past the lip.


Once out; you will see that the inner piece is simply a plastic tube (under the moulding with spade lugs on it) with one wire going down its centre and another running down the side of it, The reed switch solders to the ends of these two wires completing the circuit between the two spade lugs at the top of the sensor. The switches lies vertically alongside the tube so that it is "surrounded" by the magnet in the top of the float when the float is in its full position.

Inspect the reed switch and its connections to see where the fault is. You should get closed circuit when the magnet in the float is held near the reed switch. Open circuit means either the switch is faulty and isn't closing when the magnet is adjacent to it or there is a broken (corroded) wire. If the closed circuit tests OK you should try for an open circuit when the magnet is moved away from the switch. If the circuit stays closed it indicates that the reed switch is faulty & is not opening when the magnet moves away from it.

Replacement glass enclosed miniature reed switches (normally open type) are available from electronics stores for about $2 -$3. Soldering a new switch in is straightforward. Broken connections to the switch can be resoldered. If the wires have broken internally fixing them could require more dissecting of the unit which might be more trouble than getting a replacement from a scrapyard.


Once repaired, the inner piece has to be fitted back into the cap/stalk unit. I filed a small taper on the underside of the flange of the inner piece so I could ease it down into the circular retaining lip on the cap. Gentle squeezing with pliers helped it clip into place: followed by some massaging of the retaining lip back to its undisturbed shape. I put some black silicon sealer around the join between the inner piece and the retaining lip to make it waterproof and to cover up the small piece of the lip that broke out while I was levering.


Viscous Coupling Test - David Hoerl <>

With the car idling and hot, use a piece of cardboard about 12 inches long and folded, and press it against the outer edge of the center part of the fan (the metal circular piece on the side facing the engine. If you can stop the fan by pressing hard, the coupling is no good.

Radiator Nipple Repair - "Norm Grills" <>

If you break off the overflow/return nipple on the radiator, it can be repaired. BMW sells a repair kit, probably because this is a high frequency problem. The part number is 17-11-9-055-593 and costs a whopping $4.52. Be REAL careful not to over-tighten it or you will crack the tank and be back to square one.