QuestionEvan you are the only one that seems to know anything about these cars, The preasure is coming out the expansion tank cap.I didnt replace tha head bolts reason being that i bought the HEADGASKET KIT from bmw dealer and they told me everything i needed was in the kit including valve seals for the refinished head ....It didnt come with haed bolts so I retorqued the old ones...Like i said the car is running great There is no bubbles in the expansion tank when running.... But you did turn me on to a new lead..The water pump I think it might be starting to leak could you tell me if that would bring on high preasure and how? Thanks for your greatly appreciated help...Jeff
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Thank you for your advice it is giving me a little hope light at the end.... If it was the water pump wouldnt the car overheat? ... It is running perfect just throwing coolant from the tank a few drops.... What is normal coolant preasure at the tank?...Thanks again your expertiese is greatly appreciated....Jeff
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Heres my problem. On my 2000 528i I just replaced the head gasket I had the head machined and magnifluxed for cracks (none were found). At the same time put Brand new (all bmw parts)radiator,expansion tank,thermostat,and spark plugs....Put it all back together The car is running great no check engine lights and running at normal opertaing temp. but it keeps building up coolant preasure and escaping from the expansion tank. we did bleed the system and also put new upper radiator hose and heater inlet tube. I am confused ? There is no oil in the coolant and no coolant in the cyclindersany help would be grreatly appreciated... P.S. did replace the cap aswell...thanks Jeff
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Jeff, check the water pump for circulation. If found good then warm the car up a little and remove the plugs and put compressed air in the cylinders one at a time at top dead center (using a cylinder leak down tester is best). Look for bubbles in the coolant. You did replace the head bolts right? and Torque them to BMW specs? Did the machine shop pressure check the head?
-Evan
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Jeff, system pressure can get up to 30psi. I was under the impression that the pressure was over flowing and activating the relief valve in the cap. Did you replace the head bolts? Are you getting bubbles in the coolant when running it? Please pressure test the Expansion tank and Radiator cap.
-Evan
AnswerJeff, the early E39 and some other six cylinder vehicles had an water pump impeller that would get loose on the shaft and sometimes fall off. You may be getting over pressure before it shows overheating. If the impeller gets loose on the impeller it won't circulate coolant through the radiator causing over temp and pressure. I would look for circulation in the resevoir (swirling coolant) while someone revs the engine. If coolant is comming out of the weap hole in the casting then coolant is getting into the bearing area. Also rubber O-rings tend to over expand when they have been overheated and don't seal well. Loosen the fan and pull the anchors for the fan shroud. Pull the shroud up up high enough to remove the fan. Use a bungee chord on the hood to the fan shroud to keep it up out of the way. remove the pulley and water pump nuts. You can use two M6 bolts in the threaded holes inbetween the pump nut holes to act as a puller to remove the pump. BMW went from a white/yellow plastic impeller to a metal impeller and back to a black composite impeller on their water pumps. The pressure has to be comming from either leaking cylinder pressure into the cooling system (tested by cylinder leak down test or chemical CO2 test) or by overheating causing increased cooling system pressure. Head bolts are onetime use only it is unfortunate that the parts department didn't mention this. I would replace the water pump first and retest. If problem persists. Perform Head gasket leakage test (CO2 chemical test). If that tests shows failure then replace the Head bolts. If that test shows no leak then carry out cylinder leak down test while engine warm just to make double sure the no cylinder pressure is getting into the cooling system (should have been revealed in chemical test). From what you describe this is a cylinder pressure leak issue and not an overpressure from overheating issue. Cylinder head bolt torque for iron block is 30Nm +90degrees +90degrees. Aluminum block is 40Nm +90degrees +90degrees. Clean and oil threads of bolts. Make sure threaded bore is clean and not full of oil or coolant. When we have an overheat issue with an aluminum block we release the head bolts and retorque the old bolts to make sure the aluminum threads in the block will with stand the torque and the metal hasn't been weakened from the overheat.
-Evan
