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Old 12-11-2019, 11:28 AM
Rotorblade Rotorblade is online now
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Possible blown head gasket

The low coolant level warning came up while driving a few days ago 100mi after a timing chain repalcement job. It seems to be leaking through the filling cap valve. I have refilled the system several time and it still looses the coolant. It goes slightly below the minimum level then the lamp lights up. After the engine cools down, even after 12h there is still a little pressure inside the cooling sytem when I open the cap.
After the timing chain replacemet, they put all the oil back and started the engine. There was a valve lifter noise and they added some more oil, approx. 0.5l, then they handed me over the car. After like 8km of city driving in high trafic the yellow low engine warning lamp came on and I stopped after a few minutes and topped up with oil. I needed to add approx 1l, so the level was like 1.5l less below maximum which seems ok. Also low oil level doesn't necessarily cause head gasket failure I suppose. After 100mi the coolant lamp switched on. During the timing chain replacement they checked the compression by hand and it was very good.
Anyway there are indications of a blown head gasket that seem to pressurize the cooling system and cause the valve to open I think. At idle if I squeeze a rubber coolant tube it doesn't feel under pressure but maybe it happens at higher load (where the pressure inside the cylinder rises more). Any advice or any idea of the cause?
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Old 12-11-2019, 12:45 PM
joelselman joelselman is offline
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I believe you can buy a kit at an auto parts store which will check for combustion gases in your coolant.
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Old 12-11-2019, 12:53 PM
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Quote:
Originally Posted by joelselman View Post
I believe you can buy a kit at an auto parts store which will check for combustion gases in your coolant.
Thanks. Yes, I was planning for that or a compression test, but I didn't check if or where I could buy the kit.
I think it's a small leak that got worse over time. I remember finding the coolant level a little low before and a little more water steam than I would normally expect.
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Old 12-11-2019, 11:10 PM
Andyz4 Andyz4 is offline
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Rotorblade, I assume they pulled the head to do the timing chain. Hopefully they torqued it correctly on the reinstall. Might be worth it to pull the valve cover and double check the head bolt torque. Have you contacted the repair shop about this?
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Old 12-11-2019, 11:27 PM
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Originally Posted by Andyz4 View Post
Rotorblade, I assume they pulled the head to do the timing chain. Hopefully they torqued it correctly on the reinstall. Might be worth it to pull the valve cover and double check the head bolt torque. Have you contacted the repair shop about this?
They didn't pull the head. If the head gasket leak is confirmed I'll tell them to check the bolts to see if there are loose ones.
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Old 12-12-2019, 07:08 AM
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There seems to be no pressure in the cooling system when the engine is cold at 35%load (inpa readout - in gear with brakes and a little throttle). So either the cap is not good or there is a leak at higher load.
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Old 12-12-2019, 09:11 PM
Andyz4 Andyz4 is offline
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I think that's normal. The water pump doesn't really generate much pressure to speak of, the pressure comes strictly from expansion of the coolant as the car warms up.
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Old 12-13-2019, 05:18 PM
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dc_wright dc_wright is offline
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Quote:
Originally Posted by Andyz4 View Post
Rotorblade, I assume they pulled the head to do the timing chain. Hopefully they torqued it correctly on the reinstall. Might be worth it to pull the valve cover and double check the head bolt torque. Have you contacted the repair shop about this?
Not necessary to pull the head to replace the timing chain on either the M54 or N52 engines. Also you can check for completely loose bolts but you can't check torque because the bolts are torque to yield.
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Old 12-15-2019, 05:01 AM
pokeybritches pokeybritches is offline
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Itís possible there is air in the system. Ensure itís been properly bled. The plastic coolant expansion tank is a common failure on the M54. Iím on my iphone and donít your Z4 model referenced.

Do you have smoke pouring out of the exhaust? If so, what color is it?

Check for leaks. Remove the undertray if required.

Blown head gaskets arenít common on any of these cars unless they have been overheated.


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Old 12-15-2019, 10:32 AM
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It has white smoke but that is common to many cars during the cold season. I have ordered a new cap and on the old one I may install a pressure sensor (from the tpms ). Anyway in the last 2 days it didn't loose coolant anymore, and the coolant lamp didn't turn on either. The coolant pressure was low everytime i've checked it by hand (squeezing the rubber tubes) therefore and that indicates I think most likely it was a problem with the valve or the cap itself.
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Old 12-16-2019, 01:00 AM
Z4530i Z4530i is offline
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Check to make sure you are not losing coolant from a leak at the base of the overflow tank (that's where the sensor is). That's a common BMW issue.
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Old 12-17-2019, 02:31 PM
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Thanks. I've just seen your reply and you were right. I've jacked up the car today and removed the engine under-shield and cleaned the expansion tank wit a rag then let the engine idle until it warmed up. The tank is leaking through one crack in the side. I'll replace it with a new one. I've ordered a new cap yesterday as well. Hopefully this will fix the issue .
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Old 01-14-2020, 12:44 PM
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Updates:
I had the new tank installed today. And additional problem now - the mechanic found the ATF thermostat damaged.
I've also installed a wireless pressure sensor on the bleed cap using an adaptor. After 40min of city driving the pressure got up to 0.5bar so no problems yet.

Ps this morning the gauge is at 0.4bar. Normally I don't see any reason why it didn't go down to zero except if air got in from the combustion chamber. We'll see if it builds up.
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Last edited by Rotorblade; 01-14-2020 at 11:22 PM.
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Old 01-16-2020, 07:18 AM
rsutoratosu rsutoratosu is offline
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The atf thermostat should be replace if you replace the tank, that part is like $20 usd.. Mine crumple when I took my tank out.. that part is really fragile (12 year old car). Have they bleed air bleed the system ?
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Old 01-16-2020, 11:28 AM
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Yes, he bled the system, but I needed to add one more litre in the morning. I had stabilized now. I didn't make bubbling noises anymore. Also, I did a 20km trip to a shopping center and the pressure got up to 1bar.
About the ATF valve it seems that only makes the fluid get warm quicker. I suppose the heat exchanger is connected to the engine circuit so when the engine is cool the circuit doesn't include the radiator. The valve can't regulate the ATF because it doesn't measure the AT fluid but it is immersed in the coolant which is not heated by the AT fluid before the valve opens. So it means it is heated by the engine circuit. The main thermostat keeps the radiator out of the circuit until the coolant warms up. With the ATF valve removed at cruising speed the coolant gets cold like 40C but the engine coolant loop is regulated to 95C+, which should include the ATF valve as well. The only weird thing is the radiator is right next to the coolant tank and the temperature in this case would vary with the radiator temp making the ATF fluid too cold.
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Old Today, 03:54 AM
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I've been monitoring the temperature and pressure in the coolant tank, it goes between 0.8-1.1bar, and 45-75C, the engine stays at 95-97C, while driving at 80-110kph. The transmission temperature was a bit lower, 85-87C(I've used INPA to get that). I've checked the diagram and the ATF thermostat is in the loop between the radiator and thermostat so it's not regulated by the engine thermostat. There are transmissions the don't use an ATF thermostat and are connected directly to the front radiator through a heat exchanger and can have extra small radiator. So the fluid won't go too low anyway. The only thing is it may heat up slower than without the ATF thermostat. I can rev the car to 1100rpm for 1-2min on neutral and then drive gently until the water temperature gets to nominal temperature to avoid problems with ATF being too low.
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