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.

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!

04/15/2014 3:27am


I am writing to tell you about a new BREAKTHROUGH method for repairing a leaking Coolant Transfer Pipe in the BMW N62 V8 engine block using the BimmerFix Stint. The N62 V8 is a popular BMW engine that was used from 2002 thru 2010, in such fabulous vehicles as the BMW 735i, 740i, 745i, 750i & Li, 645Ci, 650i, 540i, 545i, 550i, and the X5 SUV.

Located deep inside of this BMW N62 engine is a Coolant Transfer Pipe, which carries antifreeze from the Water Pump to cooling chambers within the engine. However, the Front Seal on this Cooling Tube can fail in as little as 40,000 miles, and start leaking antifreeze from the engine block, through a weep hole in the Timing Chain Cover. When this happens, the car will lose antifreeze from the engine, and the engine will overheat.

In the past, this has been a very expensive repair because it required disassembly of the engine, in order to access the leaking Cooling Pipe Seal. The original method of replacing the crossover Coolant Transfer Pipe required the removal of the Timing Chain Cover. This repair could cost $6,000 or more at the BMW Dealer.

Then, an after-market Collapsible Coolant Pipe was developed to save time and money on this repair. This Collapsible Coolant Pipe method involves removing the Intake Manifold, cutting out the old Coolant Pipe and installing the after-market Collapsible Coolant Pipe. But even this method required many hours of shop labor and expensive parts and supplies. The repair bill for this method can still cost between $1,500.00 and $2,500.00 to remove the Intake Manifold, cut out the old Coolant Pipe and install the new Collapsible Coolant Pipe.

However, BimmerFix Products Co. has discovered a BREAKTHROUGH system to stop the leak! The BimmerFix method is much faster and less expensive than these old methods. This simple, yet durable and long lasting method inserts the BimmerFix Stint into the leaking crossover cooling tube, through the Timing Chain Cover. The thin aluminum sleeve creates a long lasting repair that is much easier and less expensive to install than the old repair methods.

The new BimmerFix Stint will stop the Coolant Pipe leak, and only requires the removal of the Water Pump. This new patent protected invention can save YOU or your customer’s time, hassle, and thousands of dollars. It works or your money back!

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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?


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