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coolant light and pressure

 
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gcoughlin



Joined: 05 Dec 2004
Posts: 5
Location: CA

PostPosted: Mon Feb 07, 2005 12:38 pm    Post subject: coolant light and pressure Reply with quote

I have a 1998 M3. The coolant level warning keeps coming on, and, almost always, the level is fine. But when I open the resevoir, even if it has been sitting overnight, there is a lot of pressure in there. Moreover, the check engine light came on, went off for a while, and came on again. It also overheated, or claimed to, right after opened the coolant resevoir cap to check the level, but right after that, a couple of hours later, it was fine again. THe engine has also started to run a little rough. Would a failed head gasket or a cracked block show these symptoms? Any help appreciated.
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edjack



Joined: 04 Feb 2002
Posts: 3887
Location: San Jose, CA

PostPosted: Mon Feb 07, 2005 7:06 pm    Post subject: coolant light and pressure Reply with quote

If you are concerned, have the cooling system pressure-tested. This will show if there are any coolant leaks.

I doubt it, since the system holds pressure overnight.
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edjack



Joined: 04 Feb 2002
Posts: 3887
Location: San Jose, CA

PostPosted: Mon Feb 07, 2005 7:08 pm    Post subject: coolant light and pressure Reply with quote

BTW, did you remove the cap while the engine was running? If so, that will cause the coolant to boil. Not a smart thing to do!

Sounds like you may have air in the system. Has the cooling system been serviced recently?
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gcoughlin



Joined: 05 Dec 2004
Posts: 5
Location: CA

PostPosted: Tue Feb 08, 2005 9:15 am    Post subject: coolant light and pressure Reply with quote

No, the engine was off when I opened the cap. The rough running, it turns out, was caused by a bad coil. I thought maybe a cylinder into which coolant had leaked might not fire well and would cause the engine to be rough.
SHould the pressure remain in the coolant system even overnight? Does the pressure normally come from gas expansion of heated liquid, or does the presence of pressure indicate that there is an air pocket? I'm not even sure what "normal" is here. Thanks for the replies.
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