E90 diesel high pressure inside coolant circuit

coiedulci · 09-28-2017, 02:50 PM

I have a 2005 E90 320d with M47 engine, automatic.
I've bought it in February and since then i have sporadic loss of coolant.
Let's say 1 liter @ 100 km sometimes. Sometimes 1 L @ 500 km.

I've only had one overheating incident in 6500 km due to oil inside coolant; that was due to a bad heat exchanger.
My coolant hoses are pretty rock solid and i get coolant around the fluid expansion cap after a 30 minutes drive.
The cap is rated at 1.4 bars ( i've already changed 3 ! ) but the coolant even thought doesn't exceeds 97 degrees Celsius ( that should be around 0.9 bars ) is thrown outside.

The only pattern that i've seen related to coolant loss is that i think i'm loosing coolant if i drive more than 15-20 km around the city.
I think i'm only loosing coolant when i've reached the 90 degrees mark and i'm driving hard ( above 3000 rpm ).

Also, around 300 km ago i've bypassed the EGR cooler coolant line.
Before this bypass operation i think i've had even more pressure in the coolant, it was very noticeable in the morning even after 12 hours of cooldown i've stil had pressure when opening the cap.

Summary:
- i have no overheating problems
- i'm loosing coolant through the cap
- i've changed the heat exchanger for the oil and bypassed the EGR cooler coolant line
- if the cap is removed and the engine is started i have no bubbles or smoke or anything, just some steam

Questions:
- is it possible to have the head gasket blown but no extreme simptoms like severe pressure from engine that would make driving impossible ?
- two mechanics said the bleeding is done automatic by the car, i don't think this; is it possible the pressure to be caused by air pockets ?
- any other ideeas ?

juld0zer · 10-02-2017, 06:43 AM

Oil is extremely difficult to remove from the entire cooling system once it gets in there. Heater cores and radiators are common items which can get clogged from engine oil contamination. A blockage can cause overpressurisation of sections of the cooling system.

There are some tests that can be done to determine if combustion gases are entering the cooling system.

So since you have changed the cap three times, are they genuine BMW caps or generics? Does a new cap fix the problem immediately or does it still spew out once the engine gets to operating temp? Engine oil also degrades the synthetic rubbers used in the cooling system. So if a new cap fixes the leak for a while, residual engine oil contamination might be the cause of the system not holding pressure.

Caps can also be pressure tested to see if they hold the rated pressure.

09-28-2017, 02:50 PM	#1
coiedulci Private 11 Rep 56 Posts Drives: F30 ED Join Date: Feb 2017 Location: Romania iTrader: (0)	E90 diesel high pressure inside coolant circuit I have a 2005 E90 320d with M47 engine, automatic. I've bought it in February and since then i have sporadic loss of coolant. Let's say 1 liter @ 100 km sometimes. Sometimes 1 L @ 500 km. I've only had one overheating incident in 6500 km due to oil inside coolant; that was due to a bad heat exchanger. My coolant hoses are pretty rock solid and i get coolant around the fluid expansion cap after a 30 minutes drive. The cap is rated at 1.4 bars ( i've already changed 3 ! ) but the coolant even thought doesn't exceeds 97 degrees Celsius ( that should be around 0.9 bars ) is thrown outside. The only pattern that i've seen related to coolant loss is that i think i'm loosing coolant if i drive more than 15-20 km around the city. I think i'm only loosing coolant when i've reached the 90 degrees mark and i'm driving hard ( above 3000 rpm ). Also, around 300 km ago i've bypassed the EGR cooler coolant line. Before this bypass operation i think i've had even more pressure in the coolant, it was very noticeable in the morning even after 12 hours of cooldown i've stil had pressure when opening the cap. Summary: - i have no overheating problems - i'm loosing coolant through the cap - i've changed the heat exchanger for the oil and bypassed the EGR cooler coolant line - if the cap is removed and the engine is started i have no bubbles or smoke or anything, just some steam Questions: - is it possible to have the head gasket blown but no extreme simptoms like severe pressure from engine that would make driving impossible ? - two mechanics said the bleeding is done automatic by the car, i don't think this; is it possible the pressure to be caused by air pockets ? - any other ideeas ?
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10-02-2017, 06:43 AM	#2
juld0zer Lieutenant Colonel 480 Rep 1,600 Posts Drives: Prev 135i 7DCT, Now 130i 6sp Join Date: Jul 2016 Location: 2153 iTrader: (0)	Oil is extremely difficult to remove from the entire cooling system once it gets in there. Heater cores and radiators are common items which can get clogged from engine oil contamination. A blockage can cause overpressurisation of sections of the cooling system. There are some tests that can be done to determine if combustion gases are entering the cooling system. So since you have changed the cap three times, are they genuine BMW caps or generics? Does a new cap fix the problem immediately or does it still spew out once the engine gets to operating temp? Engine oil also degrades the synthetic rubbers used in the cooling system. So if a new cap fixes the leak for a while, residual engine oil contamination might be the cause of the system not holding pressure. Caps can also be pressure tested to see if they hold the rated pressure.
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