Coolant light

R

Reecebmw

New member
Hi all,

Just bought a z4 my2005 this weekend - enjoying most things so far!

The coolant light came on, so took it to BMW - they ran a pressure test, and also did their safety and inspection check, topped up coolant, oil, etc. There is a little bit of oil under the car that needs further inspection, but they have it the all clear.

Driving it home, the coolant light came on again - I did have to drive a bit of distance as I was returning home, no rough running, no smoke, no overheating (gauge it otherwise), no residue near exhaust. There is a little drip from the driver side under the bumper near the screw, which smells like coolant.

I'm going to check the coolant again shortly (got some bmw coolant), but the car was also bought as I need a daily driver this week. Getting a full service on Friday.

What do you think? Sensor or anything else I can check?
 
It's nearly always the plastic expansion tank which develops a hairline crack and only leaks when the coolant is fully up to temperature and under pressure.

The O-ring around the tempertaure sensor is also a possibility but nowhere near as common as the above.

Reecebmw said:
If it was the expansion tank or hoses, wouldn't that show up on a pressure test?
Click to expand...

...that is assuming that BMW did the test with any degree of competence. Unfortunately, on my experience with main dealers I expect that to be fairly unlikely!
 
If the light is coming on and off, it may well be some air stuck in the system. Had that myself after changing a load of the cooling parts, took a couple of bleed cycles to get everything happy.
 
Hey man I bought my 06 Z4 back in August and had a similar issue. I'm now very up-to-date on this issue and common causes for you to check. Feel free to PM.

Anyway - what has already been said is true - coolant expansion tank is common failure. Would give it the good old fashioned eye test (you only have to remove one small cover on the engine which you can find on youtube how to do if you type in BMW Z4 coolant expansion tank).

The next thing to check is upper radiator hose - very common to find small cracks there. This was leaking in addition to my expansion tank.

You may also ask the owner if the previous expansion tank was changed. The off-brand expansion tanks (like the one i put in originally) have a faulty "float" which will get stuck and trigger a low coolant light when, in fact, you aren't low on coolant.

Lastly, there could be air in the system. There is a procedure to bleed the air out that you can find on youtube. Some are a bleeder screw, and others have a sequence that involves electronics and only requires you to push down the gas pedal etc. Google your engine, youtube the procedure for that engine. Do the bleeding procedure 3-4 times.

Good luck!
 
Had my local mechanic check- the leak is from a broken window washer, and the radiator definitely has no problem, and he's said it's the sensor.

So, will be getting those things fixed.
 
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