Question about BMW 330

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I have a 2004 BMW 330i and have replaced everything in the coolant system, and my vehicle is still leaking coolant out the expansion tank, or the cap where you add coolant to the radiator. I have use OEM parts and have changed some of them even twice without even driving the car one mile. I have put two new thermostats and two new expansion tanks and caps on the vehicle, a new water pump, new hoses new fan and fan clutch, pulley, you name it I have replaced it. There is no oil in the coolant nor coolant in the oil. It shows all signs that the thermostat is stuck closed, the bottom hose is cold after up to an hour of idle, however once the vehicle is drove, even a few feet the car starts to loose the coolant out the expansion tank. Any Ideas at all Please let me know. Thak you for your time.

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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.

Posted on Jan 30, 2010


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Why is water leaking from expansion tank when engine turned off on vw 1996 polo

There should be two level markings on expansion tank; one for cold engine, and the other for normal running temperature ( hot ). Check level after vehicle has sat for a few hours or parked overnight and make sure it is at the cold level of expansion tank marking. This will allow room for expansion of coolant when engine is in use in expansion tank.

Jul 04, 2014 | 2000 BMW 3 Series

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2004 bmw 325ci water leaking under expansion tank

remove the expansion tank and have a look at the seams those tanks have a habit of distorting and start leaking

Feb 07, 2013 | 2004 BMW 325i

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If expansion tank was low on coolant, will this cause my bmw to overheat? and where is the expansion tank located on my car?

Under filled cooling systems generally do not cause a "hot" running vehicle, there is most likely a mechanical problem some where. the expansion tank on all BMW's is usually a "yellowish" colored reservoir with a black cap, the only exception is the later models that have the expansion tank attached next to the radiator (they are black with a black cap.

Apr 26, 2011 | BMW 325 Cars & Trucks

1 Answer


Are you talking the expansion tank? If so - Drain coolant first by going underneath the car and take off the protective shield and unscrewing the blue plastic screw (make sure the car is NOT hot!), under the reservoir you'll see an electronic sensor - carefully twist is a 1/4 turn counterclockwise and gently pull downward to remove this sensor don't force it, you don't want to pay $150 to replace it. Disconnect the hoses on the top and bottom of expansion tank by pulling up the metal tabs upwards then pulling the hose away from the tank. I believe there are two or three screws which hold the expansion tank bracket in place, unscrew these and pull the bottom of the tank away from the radiator then lift upwards on the bracket (the bracket and expansion tank should then come out). Get the old expansion tank off the bracket and replace. You want to take off the bracket because getting a new tank on the bracket is a B*TCH!

Reconnect in reverse order.

Make sure to bleed the cooling system properly to remove air pockets (please use BMW coolant and distilled H20 in 50/50 mix - it's not the same as your Prestone or other mass produced coolants). Last replace the expansion tank cap because that might have created the expansion tank cracking.

Good luck and hope this helps

Dec 16, 2010 | 1999 BMW 323 Series

3 Answers

I put too much coolant into my 2001 BMW 330i and need help!!!

Look on the upper hose. There should be a plastic srew and you should have a srew right next to the cap. I had these on my 2000 528i. Hopefully you did not blow up the coolant bottle which is usually the weakest link on these. Blow into the the radiator thru the radiator cap to see if it holds pressure..

If it doesnt then you will need to replace something first. If everything looks ok open the screws, the lowest one first then the upper one. That is if you have 2.

Then you may need to run the engine up to temp then shut the car off and let it cool off. Each time open the bottle and check the level. You may need to do this a couple times or more.

First coulple times you drive the car have some coolant with you in case it starts to overheat. Keep an eye on the temp. Especially in the first several miles.

Jan 15, 2010 | 2001 BMW 330

2 Answers

My BMW 330i is still running hot after replacing the thermostat and housing, fan, fan clutch, auxiliary fan and flushing the radiator any suggestions as to why?

It could be several reasons...1. make sure you dont have to bleed the coolant system, on some cars you have too, because there is air in the system, and the car will overheat..2. Your waterpump maybe bad also..3. Double check your coolant temp sensor, and or coolant temp switch..maybe faulty..4. Check your radiator cap...seal could be bad, and not sealing correctly...Question..How long does it take before it overheats...and are you getting any white or grey smoke out of the tailpipe? If so, then your head gasket is blown...Goodluck

Dec 04, 2009 | 2004 BMW 3 Series

1 Answer

I got 2001 bmw 330i series, had a leak at radiator, replace radiator, reservior and thermostat, is overheating after repairs, i thing there is an air pocket, found bleeding screw at reservior, but did not...

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

May 03, 2009 | 2001 BMW 330

1 Answer


replace your coolant reservior cap; the rubber ring has become brittle and "steams" the coolant out as you drive

Apr 21, 2009 | 1997 BMW 318

1 Answer

Water leaking from top of expansion tank.

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

Apr 03, 2009 | 2000 BMW 3 Series

1 Answer

Water leak from top of expansion tank.2000 BMW 316i se

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

Apr 03, 2009 | 1992 BMW 3 Series

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