I need help...I have a 98' bmw 740il about 6 months ago i got a leak in the expansion tank, replaced it then thermostat went out, replaced it thought my troubles were over then the water pump went...replaced it...every thing was good for about 1 month and the check coolant light started coming on everyday...noticed a leak in the rear of the engine somewhere when the car gets hot it almost pours out and theres steam and light spray back there...haven;t found the leak yet....thought it was the gaskets of the water pipe in the rear but changed those and still happens...any ideas????....i miss driving my car.
I had a water leak on my 730i I found it after much trouble.A hairline crack in the plastic thermostat housing which onlly opened up when hot and of course got worse as water level dropped.Hope this helps.
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Best test,,NAPA sells a combustion leak tester(balkamp #700-1006) A tube of liquid that will change color if combustion gas is in the cooling system.Thinking you may be right about a head gasket problem or possibly a crack in the head.
It comes with instructions and is cheaper than having a shop guess at the trouble.
I am not aying that this is what I think it is but I found this on your year BMW
Some BMW, Volkswagen and Audi cars have a common problem that the water pump
impeller becomes dislodged from the input shaft of the water pump
leaving the water pump looking ok from the outside, but failed on the
inside. If your car experiences this problem it will over heat rapidly
much like a thermostat failure. For exact specific repair procedures for
this repair visit our online repair manual page.
Failed BMW, VW, Audi Water Pump
Check Water Pump Operation
- To troubleshoot this problem first drain about a half a gallon out of
the cooling system, next remove the thermostat from the engine. With
the thermostat out start the engine (stand back) coolant should be
forced out of the thermostat port, if not the impeller has dislodged
itself from the water pump input shaft and needs to be replaced. To
replace the water pump finish draining the remainder of engine coolant,
remove the serpentine belt and coolant hoses. Next remove the water pump
mounting bolts and remove the water pump. Clean gasket surfaces and
reinstall new water pump and reassemble. Refill with coolant and recheck
system, top off engine coolant after it has re-cooled.
We have had some similar problems with some BMW's,the last one we replaced the expansion tank.Before we attached the upper radiator hose to the radiator we filled the engine with antifreeze through the hose.Install the hose and fill your expansion tank to the proper level and run the engine to operating temperature.
if you replaced the thermostat thats actually connected to the engine and not the thermostat thats underneath the expansion tank/reservoir, I would recommend filling the expansion tank to the top remove bleeder screw and allow the vehicle to sit keeping coolant filled to the top of reservoir, once you feel there is no more air in system reinstall bleeder screw and correct fluid level in expansion tank. There are a couple different tools that are used to properly bleed the system. one tool you can pull a vacuum on the system and when the vacuum is released coolant is pulled back into system. At the same time you could have a blown head gasket. There is also a tool out there to check for combustion gases in your cooling system which would be a signs of a blown head gasket. Another recommendation is to pick up a cooling system pressure tester (can be picked up as a loan a tool @ autozone) usually pressurizing the system will help to remove air pockets
have you replaced the bleeder screws? and the expansion tank cap they both have O-rings that compress and will fail over time also check the hose at the top of the exp tank it also has o-rings inside it
The water (coolant) in the expansion tank will rise and fall with the engine temperature. What the expansion tank does is collect and return coolant to and from the engine. When the engine warms up the coolant gets hot, builds up pressure and opens up the radiator cap. The coolant then goes into the expansion tank. Now when the engine cools down the pressure drops in the cooling system and the pressure drop (vacuum) pulls the coolant back into the engine via the radiator cap. The radiator cap allows the cooling system to build up pressure and by doing so increases the boiling point of the coolant, but when that pressure exceeds the caps rating the cap opens and the coolant goes to the expansion valve. The cap has another part to it that when the engine cools down and a partial vacuum is created in the cooling system a "valve" in the radiator cap opens and allows the coolant to be drawn back into the engine. I would look at your radiator cap to see if any gunk or build up is on it, and check the rubber gaskets for cracks. It's easiest just to replace the cap because they are inexpensive and easy to replace (2-10 dollars). The expansion tank should have two hoses on it. The one on the bottom comes from the radiator and the one on the top (possibly part of filler cap) runs down and is open to the ground. That way if it is overfilled or becomes overfilled it will slowly leak onto the ground. When and if you change your radiator cap, make sure the engine is cooled down, remove cap and start engine and turn heater to full blast, full heat. Leave the cap off and let it run until engine warmed up. This should burp out any air pockets that may have happened when coolant was changed. Also top off the coolant in the radiator while it is running. Hope this helps and good luck
I wonder why the overheating caused you to change the engine instead of checking with the cooling system. Some time back my 323i overheated and coolant expansion tank burst open, but that probably due to ignoring the coolant level low light for a couple of days. I replaced the coolant expansion tank, thermostat and few hoses connected with the tank and it worked fine for me.
Try to check you coolant level - may be you should have replaced your water pump and not the engine.