QuestionI have a 97 528i and at an idle it begins to overheat rapidly, but on the highway the temperature stays normal. the fan is working fine,the coolant levels are good but when the car is at an idle i squeezed the coolant hoses and it felt like there was no pressure or water flowing through them. i know this could be the water pump or maybe the thermostat. how would i be able to determine what is causing the overheating? and how would i go about fixing it myself so i don't have to spend a fortunr at the bmw dealer? please help!
AnswerHi Matt,
First try to move the fan and pulley connected to the waterpump for if it wobbles then the pump is defective and also leaks even if you don't see it. Look also for the obvious like a leaking thermostat or waterpump(look at the bottom area of the waterpump that is hidden from view and the backside of the pulley connected to the waterpump for leakmarks). If any of them leaks then you have to replace them(one or both). If there is no visible leak then proceed with diagnosis.
Very often, air inside the cooling system causes overheating.
When the engine is sufficiently cool to open the radiator cap,
remove the cap, then open/remove the vent screw in the left side of the thermostat until there is a solid stream of water
coming out(add water if needed), then close the vent screw.
Next open the vent screw in the expansion tank(where the radiator cap is) and do the same. After closing the second
vent screw, start the engine and rev it up to about 1,500 to 2000 rpm-- until you see a solid stream of water coming from the hole on the top left side of the expansion tank. While the engine is still revved up top off the water then close the cap. Now there is no more air inside the cooling system
and this is called bleeding.
Roadtest it and see if it would still overheat( a 2 mile roadtest is enough). If it does, then replace the thermostat
because you may have a sticky thermostat. And whether it is good or bad, a thermostat that has already overheated is best replaced. Then bleed it again
as per instructions already mentioned. Roadtest again and see if it is now OK. All of the above directions assumes that the waterpump is working(this can be verified by looking for signs inside the expansion tank that there is water movement).
Replacing the thermostat is easy for you do not have to remove a lot of things. But replacing the waterpump is somewhat hard since you need to detach the radiator fan with a 36 mm open wrench, then detach the alternator fan belt from the waterpump pulley with either a torque or hex socket (pulling to the left on the tensioning pulley which is the 2nd pulley from the top going down on the left front side of the engine), remove the waterpump pulley with its 4 10 mm bolts, and then removing the waterpump itself after removing its own 10 mm bolts. Do not pry off the pump in between its sides and the engine, just be patient and pull it forward.
Or, use 2 long 10 mm bolts as a pusher/puller in the extra holes found in the pump.
These may be a mouthfull of instructions. Tell me if you need more help. Regards,
