Coolant blow off

Tiny
Z4 CALI TO SD
  • MEMBER
  • 2004 BMW Z4
  • 2.5L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 123,000 MILES
So my coolant drips slightly from a unknown place. This started after my coolant blew out while idle in a parking lot. It never overheated or showed over running temperature on gauge. I filled it up bleed the system and got it home. Now everytime I start it it runs fine then when it reaches running temperature blows off all coolant from a unknown place I just moved left my jack with my father will buy one soon. Need to know if anyone has a checklist of things they could suggest for me to check. When I do I have experience with 05 x5s that's all simple small things never had any issues before with coolant just had the car gone through by Napa before I moved. I drove it 1,600 miles then this happened it drips slightly while just sitting or running then suddenly pours all coolant out at about running temperature and never overheats. I have done that twice once on accident the first time then to see if it happens again the second wherever it blows out from is not visible from above no coolant visible above near cap or reservoir just under pours out from somewhere maybe a blow off valve? Idk saving money for parts rn buying jack this weekend.
Thursday, January 7th, 2021 AT 7:59 PM

4 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
We need to check for a blown head gasket to start. However, the other possible cause is you still have an air pocket. When you have an air pocket it expands when it heats up and it just pushes the fluid out.

We need to start with eliminating the head gasket so I would test this when it is hot before or after it pushes the coolant out. Just don't refill it completely so that you can get this tester on the coolant bottle. You need to do it when it is hot or the head gasket may be sealing back up when it is cooled off so you want to test it when the issue happens.

https://www.2carpros.com/articles/head-gasket-blown-test

https://www.2carpros.com/articles/symptoms-of-an-overheating-engine

If there are no combustion gases in the coolant then we need to go back to bleeding the coolant. A trick that may help is to jack up the front corner that is the coolant bottle is closest to. This will help force the air to the highest point and allow it to escape.

Let's try this and go from there. Thanks
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Saturday, January 9th, 2021 AT 7:16 AM
Tiny
Z4 CALI TO SD
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Okay, thank you so much. I will be doing this tomorrow. Can a head gasket blow without ever being overheated? After I do this how would I go about checking a head gasket?
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Saturday, January 9th, 2021 AT 1:01 PM
Tiny
Z4 CALI TO SD
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Sorry, I just saw the link to the tester. Lol
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Saturday, January 9th, 2021 AT 1:02 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. Glad you saw it. To answer the question, yes you can. A head gasket can fail without an overheat. It is most common for a head gasket to fail after an overheat but we need to eliminate it or we could be chasing our tail by assuming it is okay.
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Sunday, January 10th, 2021 AT 3:25 PM

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