E90 - Coolant Leak - Subsequent Steps?

[Hypabl]

I possess a 330D M Sport E90 and believe I have maintained it rather diligently. It has 140,000 miles and has undergone numerous preventative maintenance procedures in recent years.

I observed a decrease in my engine coolant level, although there were no discernible leaks on the driveway. I had it pressure tested, and they verified that there were no exterior leaks.


I presume this likely indicates a head gasket issue. If that is the case, then I am profoundly disheartened! What actions may I undertake to verify whether it is the head gasket?

[Startle]

Is there any white smoke emanating from the exhaust, pollution present in the coolant, or any misfire codes detected?

What is the amount you are adding?

[Hypabl]

I do perceive smoke, but it appears ordinary to me. Nothing superfluous? I have not rescanned it for codes. If the coolant were at full capacity, the tank would likely be entirely depleted by approximately one month after covering around 150 miles.

[Nekomp]

Automatic or manual.

[Hypabl]

Automatic

[Nekomp]

The gearbox heat exchanger is known to lose coolant without exhibiting visible leaks.

[Nekomp]

https://www.realoem.com/bmw/enUS/showparts?id=VC32-EUR-06-2006-E90-BMW-320d&diagId=17_0315

 

 

Edited 3 hours ago by Nekomp

[Hypabl]

Thank you. Is the sole method to eliminate that possibility to replace it?

[Nekomp]

It is primarily a matter of inspecting for dampness, as a gradual leak such as yours will not produce a puddle; the heat exchanger facilitates evaporation. However, you should see either desiccated coolant or a moist area. If the leak were into the gear oil, the gearbox would exhibit malfunctions.

[Mastervest]

Consider replacing your expansion tank cap. My partner's B48 engine Mini and my previous 520d both experienced unexplained coolant loss, which was rectified by replacing the coolant cap.

Although our rate of loss was significantly lower than yours, this may not be the issue unless your caps or seals are severely compromised.

[Videoman]

At the end of last year, I had to replace the radiator, and one of the additional components I needed was a new expansion tank lid due to the inner rubber seal being cracked and dehydrated. Interestingly, I replaced the petrol tank cap myself approximately two months ago for the same reason, and ultimately, it is down to general ageing and wear; hence, it is entirely plausible that you are experiencing leakage from that cap. I opted for the replacement OEM part from the dealer, priced at £26, to ensure the release pressure was accurately calibrated for my engine.

It may be prudent to take a risk initially before engaging in further costly inquiry, and at the very least, it serves as an additional measure for future-proofing and preventative maintenance.

[MamaKiddo]

A hairline fracture in the expansion tank may be present, becoming apparent only when the engine is heated; I experienced this issue with my E46.