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Old 11-04-2008, 12:41 PM   #1
pyro623
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Lightbulb conifirmation

Ok here is the deal. #1 I have a coolant light on. So I started diagnosing. I think my thermostat is stuck closed for these reasons , first the top radiator hose gets hot & the bottom stays cool during normal operating tempature. Two is the heater is not blowing hot air when running normal operating temp. The one thing that throws me is that my car is not overheating like I thought it would with a closed thermostat. Do you think that having the thermostat closed will make my coolant light come on ? I thought it may due to the fact that if its closed its restricting the amount of coolant flowing through the system.By the way I replaced the water pump with no problems & didnt have this problem until I did. I am somewhat boggled!

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Old 11-04-2008, 01:02 PM   #2
TxZHP04
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You most likely have air in the cooling system and need to re-bleed it.
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Old 11-04-2008, 01:20 PM   #3
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No I dont think so , If there was air in there it would overheat which it is not. I have mechanical experience & have done the water pump before on this vehicle with no hang ups.I have noticed I do have a drip leak on the bottom hose passenger side but I dont think this would make the low coolant light come on do you?
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Old 11-04-2008, 01:25 PM   #4
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Faulty temp sensor will do this too. Its on the lower coolant hose near the radiator and quite possibly the source of your leak as well.
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Old 11-04-2008, 01:29 PM   #5
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Yes shorty this is where the leak is. Are you telling me this sensor will throw the coolant light?
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Old 11-04-2008, 01:37 PM   #6
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All depends on where the air bubble is. If you have a known leak, then you have an air bubble in the system - something has to fill the void left by the escaping water. Fix the leak and re-bleed.

I honestly don't understand why people will replace a water pump and not replace the hoses, thermostat, expansion tank, etc all at the same time. Do it once and be done with it.
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Old 11-04-2008, 01:51 PM   #7
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Txzhp04 well I will try this & see where it leads. I have not had problems before with the cooling sytem other than the water pump. My hoses & expansion tank are in good condition & I dont want to spend money if its not a have to. If I had the bucks to replace everything I wouldnt be here posting though lol.
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Old 11-04-2008, 01:55 PM   #8
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If I'm not mistaken, it's part of the coolant monitoring system. There are 3 sensors that work in conjuction with the t-stat and they all link together to produce temp and level readings. Also if you have an auto HVAC, they provide info for it too. I've never heard of it happening before, but with how electrically integrated our cars are, it wouldn't surprise me if this sensor was causing the problem. If you have a Bentley, I believe there is a test procedure for it. But if its leaking, you probably need to replace it anyway. Just another place to look.

Like Tx said, doing a quick bleed may eliminate the problem too. It only takes a few minutes. I learned not to be surprised by simple things that cause a problem which I would overlook or simply rule out.
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Old 11-04-2008, 02:12 PM   #9
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Originally Posted by pyro623 View Post
Txzhp04 well I will try this & see where it leads. I have not had problems before with the cooling sytem other than the water pump. My hoses & expansion tank are in good condition & I dont want to spend money if its not a have to. If I had the bucks to replace everything I wouldnt be here posting though lol.
If the leak is from around the sensor in the lower radiator hose, see if you can find a suitable replacement o-ring. BMW only sells the o-ring with the sensor and you probably only need the o-ring. If that fixes your leak, then re-bleed and see where that leaves you. Don't bother re-bleeding until you've cured the leak.
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Old 11-04-2008, 02:20 PM   #10
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ok guys thanks for the replys. So from here I would say its safe to say its not the thermostat since shes not overheating would you agree. Even though the heater isnt blowing hot & the lower hose is cool. That sensor is only $20.00 so Ill buy one I see what happens.
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Old 11-04-2008, 02:21 PM   #11
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Originally Posted by TxZHP04 View Post
If the leak is from around the sensor in the lower radiator hose, see if you can find a suitable replacement o-ring. BMW only sells the o-ring with the sensor and you probably only need the o-ring. If that fixes your leak, then re-bleed and see where that leaves you. Don't bother re-bleeding until you've cured the leak.
Good point. I was suggesting replacement of the sensor by assuming () that the leak is between the base and body of the sensor. Again, sometimes the little things. Like a .94 o-ring .
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Old 11-04-2008, 03:09 PM   #12
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Originally Posted by pyro623 View Post
So from here I would say its safe to say its not the thermostat since shes not overheating would you agree.
Lesson number one when troubleshooting is to assume nothing until the problem is solved.
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