So your low coolant (antifreeze) light came on and your coolant level is low. You have a leak, but where? BMWs have multiple components in their cooling systems and any of them could cause a leak, however the most common of coolant leaks are caused by a failed Coolant Temp Sensor located (in most cases) in the lower radiator hose
Checking the sensor for a leak is simple, just open your hood and look down at your lower radiator hose, find the sensor and you can see coolant remnants originating from the sides of the sensor and you should see a pool of coolant under the hose onto your lower engine panel.
Replacing the sensor can easily be accomplished by the average DIY guy, or gal. First step, make sure the cooling system is NOT hot! Open the reservoir aka (expansion tank) cap to relieve the pressure. Screw cap back on. (Putting cap back on is important if you don't want a mess) unplug connector, squeeze tabs and lift sensor out of radiator hose. Some coolant will come out but not much. Install new sensor (it comes with new O-Ring) and plug electrical connector into new sensor. Now you need to correct the coolant level (make sure not to overfill the system) Perform a cooling system pressure test to ensure no other leaks are present. Put on cap and clean off the spilled coolant with water. Your done!
Electrical connector unplugged
Removing faulty sensor from lower radiator hose
Correcting coolant level with Factory OE BMW coolant
Fluid level is correct when float reaches top (don't overfill for it can cause more leaks to occur)
Pressure test to make sure no more leaks are present
Coolant Temp Sensor Part number 13621433077
This is the coolant temp sensor that you will need to replace. Part Number is
13-62-1-433-077 and will cost about $30.00 from the dealership parts dept.
The same part is applicale for many modles including: E38 E39 E46 E52 E53 E60 E61 E63 E64 E64 E65 E66 E70 E70 E71 E72 E82 E83 E85 E86 E88 E90 E91 E92 E93 F01 F02 F04 F06 F07 F10 F12 F13 F30

10/2/2013 03:37:50

Great article! Thanks! I will try these before my sweet grandbaby gets here in October. I need some for the boat.

2/22/2015 03:13:16

Hi Jamie my bmw 325i 2004 , heat was going out. It was only working when I'm driving but not idoling. Now it doesn't work at all. My blower is working but no son saw I had a coolant leak. Could this be the problem?

2/22/2015 08:19:01

A coolant leak can cause a no heat issue. I recommend fixing the coolant leak and then see if you have heat again.

5/5/2015 12:51:51

There is a valve which lets coolant in and out of a heater core (the name i used might be wrong) this valve sometimes fails shut. this means no hot coolant goes into the core in order to blow hot air. I do believe its a simple fix or replacement. youtube has a video of someone replacing this. goodluck :)

6/10/2015 16:21:20

even though the side tabs are pushed in the sensor wont lift out any recommendations on how to get it out to put new one in

1/4/2014 10:44:10

Excellent, I thought it was the lower hose that was leaking, but luckily I read your page and checked the sensor, sure enough it was the culprit. Thanks!

kevin whaley
9/12/2014 00:51:10

I have a 06 325i e90 qhich I started losing coolant I'm but ots not a constant leak sometime I can go a week or so bedore low coolant light appers others I can't go 15 miles. Also not every time I've checked did it need coolant sometimes it was still full any suggestions?

9/12/2014 06:59:49

I will need more information in order to help you out. When you say the cooling system is "full", do you mean the coolant is all the way at the top of the expansion tank (reservoir)? I see this a lot and it's a common mistake, make sure the floating red plunger is level with the top of expansion tank when the engine is cold only. When the light is on and you check coolant level, If the coolant level is ok then you have a problem with the sensor, wiring or the expansion tank float. hope this helps. Thank you

9/12/2014 15:07:52

Hey jamie what i mean by full is I fill the expansion tank to the correct level and it will leak out but its not consistant sometimes it will last days others just 15 miles or so also not every time my coolant light has came was my resivor empty a few time its been full and doesn't appear to have lost any coolant

1/3/2015 14:18:09

I have a BMW 745i and my coolant light on my car comes on ever day if not every other day I'm constantly putting in coolant I'm curious would it be a hose leak or the sensor needing to be replaced?

1/3/2015 17:02:07

I've been having a problem with mine boiling coolant out of the overflow then relized it only happend when I ran the ac or heat after months of researching and replacing thinhs it turned out to be the waterpumo caise the issue due to something inside it breakeing and the extra stress of running ac or heat caused the car to start running warmer than normal

Michael Nelson
1/13/2015 23:48:11

No need to replace the sensor. It is the green O-Ring only that has failed. They are notorious for loosing resilience.

Purchase a hardware-store #31 O-Ring & reuse all else.

1/29/2015 23:05:12

Does the transfer pipe fix work for 2001 740 engines?

Jamie Caldwell
1/30/2015 07:25:57

The engine in your 2001 740 is different then the N62 BMW used in the 2002-2011 7 series so the famous coolant pipe repair will not apply to your car however other coolant leaks are common with your engine (M62).

1/30/2015 17:13:26

So how do you fix that pipe without losing a arm and leg

Jamie Caldwell
1/30/2015 19:26:23

What pipe are you referring too? The coolant pipe for the N62 or do you have a coolant pipe leaking on your M62?

2/2/2015 22:39:39

I did an overhaul on my cooling system..(radiator,thermostat,water pump,clutch fan, pulley, upper radiator hose, and belts) 18 months ago. I now have a leak from the top area of my e39 bmw. My system started blowing out cold air. I checked my coolant level and it was extremely low but my car never ran hot. I put coolant in an seen a leak coming from the top driver side of the radiator. could it be a pin hole leak from the radiator or is there a hose that i could be coming from?

3/17/2015 16:29:13

I have a bmw f10 2011... loosing coolant all the time no visible signs of leaks.... new expansion tank and new thermostat fitted still loosing coolant any ideas? Thanks

3/18/2015 10:10:59

I had the same issue it turned out to be the water pump

3/28/2015 08:48:05

Hi there i have a 2000 x5 with a vanos motor. I have been experiencing a horrible coolent leak it appears to be swapping from the resivoir cap. Also i have just had the time chain and guides changed twice (the first mechanic only replaced 3/4 and the forth went. The passenger vanos replaced on yet there is still a small knock when it warms up not when its cold. Over 6000 dollars have been invested in my vehicle with no signs of working properly again. Do you have any experience with theae issuse. Its an amazing vehicle and dont want to get rid of it.

4/25/2015 09:31:41

The leak may also comes from the manifold, behind the water pump, a small pin hole (bottom left); this mean the problem is inside, see video on YouTube on how to fix it. 5-7k at the dealer, 1k if you order the kit.

5/13/2015 18:29:03

That and there is a recall on lots of BMWs because of a faulty radiator cap that has to be updated with the new one.
Took me way too much work to find this out

5/18/2015 15:54:27

why is my 2003 316 chucking water out the expansion tank and my heaters are cold cheers

5/27/2015 04:30:56

Will admit, this is my first BMW and once i got it all nice and fixed up.
I really like it, love it!

6/17/2015 23:37:47

Hey Jamie my panel flickers and my ac isn't cold and I don't have heat also a coolant leak where I believe is where a sensor is at could this faulty sensor make other parts of the coolant system not work

7/1/2015 04:32:31

I was very pleased to find this site.I wanted to thank you for this great read!! I definitely enjoying every little bit of it and I have you bookmarked to check out new stuff you post.

7/23/2015 03:17:22

Hi I have BMW x5 2008 and I was looking coolent is not cercle and fan is running all the time , is it could be the water pump or the sensser?

8/7/2015 18:00:10

I have a 2010 750 and I earlier the low coolant light came on and I parked it now it's a hour later my neighbor come knocking on my door saying the car was smoking after it's been setting for a while can someone please tell me what's wrong??

8/12/2015 16:25:14

I have 2001 X5 3.0i which I am having same problem. It sometimes
loses coolant everyday and sometimes every other day. I kind of
made routine assumption that everyday I have to add about 8 ounce
of coolant after driving 10~15 miles.

There is coolant dripping under the Radiator Reservoir on near
Driving side but it is not significant amount. To trace batter I removed
the bottom plastic panel so that I can go under the car and trace it.
There is no visible crack or broken on the wall of Reservoir or Radiator.
Can any one help me what is next thing I can do ?


Jamie Caldwell
8/13/2015 22:03:27

It sounds like you have a leak from your expansion tank or radiator. I recommend to fill your cooling system with water, pressurize the system and see where the water comes from. I suspect the expansion tank to have a hairline crack that is impossible to see until the leak is active.
If you don't have a cooling system pressure tester, start the engine and let it run until it reaches operating temperature then shut the engine off... It will defiantly be pressurized at this point until the coolant leaks out. Good luck!

8/16/2015 13:46:51

Have aX5 2002 . The engine was misfiring and rough idling. The mechanic replaced everything from coils to spark plug to Crank shaft sensor and oxy sensors. Now if the engine gets started in the morning there comes a little smoke from one of the exhaust and disappears after 30 seconds the engine idle a little rough for a moment. I also loose some coolant but no visible leak.
Can someone help or have some suggestions.

Jamie Caldwell
8/16/2015 22:33:44

It sounds like you might have coolant leaking into your combustion chamber from a failed head gasket. A good technician should be able to test for combustion gases in your cooling system.


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