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General E46 Forum
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Old 06-09-2012, 10:34 PM   #1
HallisterJ1
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Is my thermostat lying to me about overheating/01 325i

I was on a hill the other night and my thermostat said extremely red hot, and when I got home and parked and turned the car off, smoke came billowing out from the hood and coolant is completely leaking from under my car. My mechanic comes over the next day and says there is the BIGGEST crack in my expansion tank like hes never seen before, so I got my expansion tank replaced it(126k stock OEM). So I start to drive around the day after with a new coolant expansion tank and coolant and stuff he installed and my thermostat reads hot as ****, but when I idle it goes all the way back down to middle (normal) and then when I'm driving it redlines again, my mechanic said it's just the thermostat being stupid and I shouldn't pay attention to it.

When I check the coolant after a long drive, there is no steam and coolant does drizzle out of it when I slowly open it too check. There are no leaks at all whatsoever.

Is my thermostat just ****ed?

No I don't have milky oil or anything head gasket related problems, my mechanic said I was fine.

I just find it VERY WEIRD that my thermostat cools down when I idle, and then when I'm driving the car it redlines and fluxuate's all over the place.

Yes it starts all the way on the left side when I start the car.
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Old 06-09-2012, 10:38 PM   #2
ac_2007
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You need to properly bleed your system.

I would not drive the car for 5 seconds if the temperature gauge went in the red. If the thermostat is right, you could have just completely destroyed your engine.
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Old 06-09-2012, 10:42 PM   #3
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Wouldn't I notice something is wrong with the engine? It idles fine, exactly how it should. Speed's good, everything seems fine. Is the thermostat just messed up?
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Old 06-09-2012, 10:46 PM   #4
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Your first answer on what to do is in my first post. Bleed it! There is air in the system.

What brand of thermostat is it? If it was a generic autozone special, there is another problem.
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Old 06-09-2012, 11:06 PM   #5
HallisterJ1
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Your first answer on what to do is in my first post. Bleed it! There is air in the system.

What brand of thermostat is it? If it was a generic autozone special, there is another problem.
That entails just bleeding the coolant from the bleed screw right next to the coolant cap right?
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Old 06-09-2012, 11:12 PM   #6
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http://www.e46fanatics.com/forum/sho...d.php?t=689618
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Old 06-10-2012, 01:22 AM   #7
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You most likely have a large air bubble in the cooling system. Your engine really is not running fine, because it is telling you that it is hot.
Any mechanic that tells you to just ignore the temp gauge is not only a bad mechanic, but he is probably also not familiar with how to bleed a BMW cooling system. It needs to be bled propperly. The links above will explain the process. I would not let that mechanic work on your BMW any more.
It is possible that there is a thermostat problem, but an air bubble is a more likely scenario. What brand of thermostat is it?
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Old 06-10-2012, 01:33 AM   #8
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Originally Posted by MJLavelle View Post
You most likely have a large air bubble in the cooling system. Your engine really is not running fine, because it is telling you that it is hot.
Any mechanic that tells you to just ignore the temp gauge is not only a bad mechanic, but he is probably also not familiar with how to bleed a BMW cooling system. It needs to be bled propperly. The links above will explain the process. I would not let that mechanic work on your BMW any more.
It is possible that there is a thermostat problem, but an air bubble is a more likely scenario. What brand of thermostat is it?
It's all OEM, but the cluster has been replaced before...It has that dot before the miles that says its been replaced. My mechanic is an ex-BMW Of San Diego Mechanic/Tech, he says my clusters just bad. I'll bleed tomorrow for sure.
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Old 06-10-2012, 01:38 AM   #9
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It's all OEM, but the cluster has been replaced before...It has that dot before the miles that says its been replaced. My mechanic is an ex-BMW Of San Diego Mechanic/Tech, he says my clusters just bad. I'll bleed tomorrow for sure.
Thats the tamper dot. Right? Meaning someone replaced and never matched the mileage too the computer?
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Old 06-10-2012, 01:59 AM   #10
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Thats the tamper dot. Right? Meaning someone replaced and never matched the mileage too the computer?
No but I have original miles on paperwork of what it should be from the previous owner. I just need an OBD to do that stuff I believe.
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Old 06-10-2012, 02:02 AM   #11
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Shouldn't your BMW mechanic from a BMW dealer ship be able to do this for you and tell you why it was like that
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Old 06-10-2012, 03:15 AM   #12
MJLavelle
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It's all OEM, but the cluster has been replaced before...It has that dot before the miles that says its been replaced. My mechanic is an ex-BMW Of San Diego Mechanic/Tech, he says my clusters just bad. I'll bleed tomorrow for sure.
I was talking about the thermostat on the engine, not the tempurature gauge.
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Old 06-10-2012, 03:24 AM   #13
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Either your cooling system has not been bled or you have a greater problem (which caused high pressure and expansion tank to crack)

One possibility is that your water-pump impeller is loose and when under load (higher RPM), the impeller spins freely on the shaft.

It could also be that the thermostat has failed and is not opening/closing as it should. The red on the gauge means your damging you engine.

There is a reason why there is a sticky that tells you to replace the whole system on failure and not just the individual parts. You will spend more money on labour and bullshit trying to fix everything individually then had you just replaced it all.
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