Care and Feeding of your 745i TurboCharger
There are 3 basic systems that help keep your turbo cool and happy.
#1.OIL SUPPLY is by far the most important, since the turbo spins at well over 100K RPM in journal bearings, it won't spin for long without it! On the 745, oil is supplied through a pressurized line from the top of the oil filter canister, around the front of the engine block, then back to the turbo where it attaches to a banjo bolt. The line itself has been known to become clogged, the bends in particular, and the end with the banjo bolt can become "coked" if any of the other cooling systems fail. Some coking may occur in the line itself if the engine has overheated, clean or replace the oil line if there is any question. Always "prime" the line and pour a little oil into the intake fitting before re-attaching. Even a few seconds without oil can be fatal! The oil return hose is very large, about 2 inches long, and just allows the oil to flow back into the oil pan. Most of us who have some experience with these cars highly recommend synthetic oil, it's resistance to coking, and overall superior lubrication qualities make it a bargain even at ~$4 a quart!
#2. FRESH AIR scoop and ducting. There is a small (6" x1") air scoop mounted under the front bumper, offset to the passenger side which ducts fresh air through about a 2" hose to an outlet pipe that is mounted on the inside fender well. The outlet pipe looks like simply a 90 degree bend cutoff so that the fresh air is blown across the turbo, midway between the turbine and compressor. This action is directly related to vehicle speed i.e. the faster the car is traveling the more air is directed at the turbo. Not much to go wrong here, check the hose for leaks, and if the car has been sitting for very long, I have heard of critters building nests in the hose!
#3. The AFTERCOOLER fan should run for 4.5 minutes after you shut the engine off, once the engine has reached 70 degrees centigrade. This arrangement consists of a temperature sensor in the block, located under intake tube # 6 (possibly on the thermostat housing on later cars), above the starter motor, a small squirrel cage type fan mounted behind the bumper, dead center of the car, a timer module, a little black box that sits just aft of the drivers shock tower, between the coolant tank and hood latch, and a ducting system with outlet pipe that provides cool outside air to a nozzle mounted underneath the turbo. I elected to restore mine to stock, using the factory VDO module ($140), but there may be cheaper alternatives. My guess is that the only reason for the temp sensor is so that the after cooler doesn't run if the car is started just to move a short distance, since the 70C temp (158F) is well below normal operating temp, and is reached after driving only a couple of miles if your cooling system is operating properly. If this fan has failed, it is probably a good idea to clean or replace the oil feed lines, as some coking has probably taken place. Also a good time for an oil change!
The wiring diagram for the VDO timer module from the fiche:
Red = constant + from battery
Red/white = + to the fan
Brown = - negative ground
Brown/Yellow = Temp sensor
Blue = + positive from the alternator
Troubleshooting the aftercooler fan:
To test first check that the Red is hot (+12v) and that the brown ground is good. If not find the problem and fix it. Some have a separate in-line fuse going to the battery.
Try jumping red to red/white and the fan should run, even with the key off, if not your fan or the wiring to it is bad.
Try a jumper from brown to brown yellow, start the car for a minute, when you shut the car off the fan should run for 4 1/2 minutes. If that works then your sensor, or the wiring too it is bad! Check the groung wire that comes from the sensor to insure that it is getting a solid connection to ground. If not you need the timer module (I got one for $140 from RODD). Haven't done a temp sensor but it looks like a major PITA.
If just your sensor is bad and you must drive the car, leave a jumper between the browns, that way the fan will run every time you shut off the car.
If the timer module is bad, you can rig a jumper between the reds and turn the fan on manually when you shutoff the car for a few minutes! I did this for a week with just a paper clip under the hood, while I was waiting for a new timer module.
GENERAL. The turbo consists of three parts, the turbine, the bearing and oiler housing, and the compressor. The turbine fan blade and the compressor fan blade are on opposite ends on the same shaft. The tolerances between the fans and housing are minute, so the slightest particle can cause instant death. Check the seals on all of the air plenum connections from the air filter on, there are several! If you must open any portion of the air handling system, be certain that no dust gets inside, and be sure that the connections are resealed completely. Most folks recommend against aftermarket air filters. The same grain of sand that would pass through a normally aspirated motor without incident, could ruin your whole day!
If all else fails and you need a new Turbo
Good News!!!
I received an Email from Robert Lowe as follows:
"If you ever need any turbo parts for 745i they are available through MELETT Products in England. Melett@aol.com. Phone (44) 1924-459200
745i KKK Turbo (K-27). The part number is 1301027712 for cartridge Cost was 363.52 including shipping. Duty was additional 4%.
The "Cartridge" is the center guts of the turbo. Includes everything from the exhaust turbine to the compressor turbine. (balanced and ready to go)
Includes gaskets for oil input fitting, oil exit fitting, and o ring for compressor housing. It does not have the oil input fitting to turbo, oil exit fitting from turbo, exhaust housing, or the compressor housing. Use your old ones. Basically replaces everything which goes bad when the thing is coked up with oil and looses lubrication"
Since I spent about $500 getting my first one rebuilt, this is good news for everybody else!
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Insuring, Titling and other red tape Deciphering the early Onboard Computer
Other 745i and BMW Links 745i For Sale Page NEW!!!!!