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


10/02/2013 3:37am

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

02/22/2015 3:13am

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?

02/22/2015 8:19am

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

01/04/2014 10:44am

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
09/12/2014 12:51am

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?

09/12/2014 6:59am

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

09/12/2014 3:07pm

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

01/03/2015 2:18pm

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?

01/03/2015 5:02pm

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
01/13/2015 11:48pm

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.

01/29/2015 11:05pm

Does the transfer pipe fix work for 2001 740 engines?

Jamie Caldwell
01/30/2015 7:25am

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).

01/30/2015 5:13pm

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

Jamie Caldwell
01/30/2015 7:26pm

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

02/02/2015 10:39pm

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?


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