Coolant leak
 

2006 3.0

So I have a strange coolant leak I can't isolate.

Entire system was replaced 2 years ago.

Leak(decent puddle) appears 20-45 minutes after car is shut off. Location is 1.5-2ft from front driver's side tire towards center of car

Doesn't leak at any other time. Was thinking water pump but location of leak on ground doesn't seem to make sense.

The problem with location is that if it hits the stiffening plate, all bets are off the original source.

Since it's relatively cool out still you can run without the mechanical fan (I didn't put mine back on yet). Remove the fan and you can easily see the entire front of the motor to determine if the leak is from motor mounted part like the thermostat.

The usual culprit is the reservoir and that is usually pretty easy to determine. Again with the fan/shroud out it is much easier to determine.

The aux pump is right above where you are describing so that might be an easy thing to rule out. You may have to remove the air box to get a look but that's easier than the fan.

Tools needed to pressurize a COLD cooling system for diagnostics

Note: STANT 12030 threaded system testing adapter is required to
test most BMW and Land Rover cooling systems with a
threaded filler neck.

Images below are for a 3.0 application

As Andrew posted it not rocket science. Pressurize, look for drop in pressure on gauge, find source!

Oh, see #4 sensor in lower rad hose? The seals go bad all the time. You can either buy the sensor with the seal or just the AFTERMARKET seal. See Rockauto.com for the $.88 seal

Somebody adapted his motive pressure bleeder and an old coolant cap which does the same job it's very nice that with the 1/2g size air tank is very friendly to volume changes not changing pressure and a decent pressure gauge. I've been wanting to do the same and kicking myself for not keeping the old caps when replacing EITHER of my reservoirs.

would only take a cap, a coupler and the pressure tank or a pump kit like above. All get you there....

The pump kit like Stant's, allows you to test something other than BMW's :)

If you make an adapter out of a bleed screw you can test everything including the cap.

I've also had good luck hunting for non-obvious leaks with a coolant UV dye kit (UV Glasses, UV flashlight & UV dye) found on Amazon. You may have to buy the dye separately. Make sure you get the dye for cooling systems, not oil.

Put 1/2 bottle (1/2 ounce) in expansion tank and run it for a day or two ..

Then at night put on glasses and use flashlight to find UV source.

I just found my leak at the heater control valve...

+1 on this. Used UV dye to find a leak that I was chasing for a month. It was the temp sensor o ring on the right side of the radiator. Leaked from there, hit the splash shield then ran out wherever it was easiest. Not where the actual leak was.

Here's the post on pressurizing using a brake fluid pressure bleeder:
https://xoutpost.com/bmw-sav-forums/...ystem-e53.html

On other cars of mine, I've made an interface for the brake system out of an old brake fluid reservoir cap, so that's what I started with here = a coolant reservoir cap. But the bleed screw interface is a lot easier on these cars. And as 80stech mentioned above, the bleed screw option allows testing of the reservoir cap, if you're brave enough to pump to 2 bar (30 psi). I partly did it for that reason, but did not go past 20 psi. 20 psi with the cap not leaking was enough for me to conclude the cap was not faulty.

In general, it will be much easier to check for a coolant leak when the system is pressurized. Cold, not dangerous, take your time with a flashlight, disassembling as needed until you can pinpoint the source.

Consider yourself lucky that the coolant is leaking externally vs. internally as many of us eventually face.

Nice


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