Cold weather headgasket leak

[bostongrun]

Hi All,

I have a 2004 X3 3.0. I live in Minnesota aka "Minne-So-Cold" We have been in a serious cold wave with night time lows of -10 to -20 f. The low coolant light came on and I topped it off with maybe 6 oz. I began to monitor the level afterwards and observed a minute loss. I saw a little coolant on top of the expansion tank like coolant was coming out the pressure cap. I pressure tested the cooling system and found a very slow depletion. I pressured the system and started the car and observed a single puff of white smoke on start up but no lingering white smoke. The car doesn't overheat, misfire nor does their appear to any water on the dipstick. The valve cover breather is a little frothy but that's normal in the winter up here. I took it to a reputable mechanic who said I should hold off on the head gasket because he said the extreme prolonged cold can be causing the miniscule head gasket leak. He explained that over thousands of warming a cooling cycles the metal in the gasket can compress due to metal fatigue. When metal in the block gets super cold it contracts perhaps .001/.0005 " just enough for a little coolant to seep through the layered gasket facilitating a little seep into the cylinder whilst a little exhaust gas passes into the cooling system causing pressurization for a short interval until the heat of combustion expands the metal enough to close the fissure.

I previously had an old 525 with an non-vanos M50 engine and I remember a BMW mechanic telling me that old BMWs tended to have minor head gasket leaks in the winter owing to the wider range in temperature exacerbating metal expansion and contraction.

Has anyone else out there heard of or experienced this ?

[mrgizmo04]

Have not experienced, but run a compression test to confirm head gasket issues.

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[MIKYZZ4]

A cylinder leakdown test will solve this mystery!

[ross1]

Sounds like the beginning of a head gasket failure. I know a car, with similar engine, that has been this way for years, it's gotten worse recently and will need addressing soon BUT as long as coolant is topped off regularly(I get a call when her heater isn't working well)it is just fine. It has traditionally consumed more coolant in winter.
Your mechanic's theory makes some sense but consider that a leaking HG is a leaking HG. Coolant bypassing it and worse, combustion gasses, will eventually kill it.
I'm in Chicago, it gets damn cold here too(0*f when I woke this morning) and I've never seen a failing head gasket repair itself. I wouldn't panic but you need to closely monitor coolant level.
You'll probably start seeing misfires on cold starts as it gets worse.

[bostongrun]

It turned out to be a leaky O ring in the upper radiator hose! Don't over diagnose !

[MIKYZZ4]

We can only diagnose what little info you gave us,
IF we were there like you, then diagnosis would be much simpler,
AND much more accurate!

Anyway, glad the problem was located,
and a fix was easily performed.

[bostongrun]

I noticed that coolant was accumulating on top of the recovery tank below the two hoses but it didn't appear to be coming out of the pressure cap. For confirmation, I put some white masking tape on top the recovery tank and added some florescent dye and sure enough there was a small dribble below the smaller hose. I also recalled a slight hiss sound while pressure testing the cooling system which I attributed to the head gasket but blown head gaskets usually don't make a hissing sound from pressure testing.

Those BMW quick disconnect radiator hoses are perfect example of BMW "over engineering " It would have been simpler to just use a clamp that could be tightened as needed but they had come up with this O Ring based idea that relies on springy wire locks are prone to flying off into oblivion rendered the whole hose assembly useless. These types of coolant connectors just don't appear to have the clamping strength of conventional. The constant vibration of the vehicle causes the male inlet of the tank to continuously elliptically press against the o ring facilitating wear.

Another lesson is don't consider mechanics advice as gospel because they frequently assume the worse case scenario.

[MIKYZZ4]

Btw, that reputable mechanic in your first post, should have easily found that leaky hose,
instead of steering you-and us, towards a headgasket diagnosis.

[ross1]

I noticed that coolant was accumulating on top of the recovery tank below the two hoses but it didn't appear to be coming out of the pressure cap. For confirmation, I put some white masking tape on top the recovery tank and added some florescent dye and sure enough there was a small dribble below the smaller hose. I also recalled a slight hiss sound while pressure testing the cooling system which I attributed to the head gasket but blown head gaskets usually don't make a hissing sound from pressure testing.

Those BMW quick disconnect radiator hoses are perfect example of BMW "over engineering " It would have been simpler to just use a clamp that could be tightened as needed but they had come up with this O Ring based idea that relies on springy wire locks are prone to flying off into oblivion rendered the whole hose assembly useless. These types of coolant connectors just don't appear to have the clamping strength of conventional. The constant vibration of the vehicle causes the male inlet of the tank to continuously elliptically press against the o ring facilitating wear.

Another lesson is don't consider mechanics advice as gospel because they frequently assume the worse case scenario.

It ain't BMW overthinking stuff here.
Nothing wrong with those hose connections and the clips only "fly off into oblivion" when dismantled incorrectly.

[shadowpuck]

It ain't BMW overthinking stuff here.
Nothing wrong with those hose connections and the clips only "fly off into oblivion" when dismantled incorrectly.

+1 - truth.

[bostongrun]

Some one mentioned there is not a problem with those clip loaded hose clamps. FYI, that hose is an OEM replacement < 4years old. It's been a long time since college so I forgot my calculus but try to visualize the amount of lateral force exerted and retained by those wire retaining clamps versus the force exerted by a hose clamp with a much larger surface area not to mention the ability to tighten the clamp to compensate for compression.

[MIKYZZ4]

The o-ring inside the hose connection provides the tight no leak seal,
the clip just provides a non-slip locking mechanism.
Nice quick release & replacement-no tools needed design!