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Old 02-09-2014, 02:00 PM   #1
thisisMikeNa
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Coolant leak after thermostat and hose replacement

Hey guys, I've been reading the forum for a while now, but this is my first post. Any help would be appreciated.

After replacing the upper and lower radiator hose, the thermostat and the coolant temp sensor, I've developed a pretty good sized leak. It a appears to be coming from behind and just to the left of where the lower radiator hose connects to the thermostat. When the car's off, it drips below from the ac compressor area.

I've bled the system and temp is normal. All connections appear to be on correctly.

Any help would be appreciated!

Thanks.
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Old 02-09-2014, 05:48 PM   #2
zhenkaaaM3
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Maybe tighten up the hose clamp at a new spot on the end of the hose?
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Old 02-09-2014, 06:09 PM   #3
thisisMikeNa
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Maybe tighten up the hose clamp at a new spot on the end of the hose?
Thanks for the reply. There isn't a clamp for the hose, there's just that metal clip. Maybe I didn't push the thermostat in far enough?
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Old 02-09-2014, 06:23 PM   #4
2003silver330i
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If it was my car I would do the following:

1. Try pushing the hose on with some force. If that doesn't do anything I would go to step 2
2. I would pull the coolant hose off and check o-ring on the inside and check the the outer plastic coupling for cracks. If those check out good than I would go to step 3
3. I would check around the thermostat opening that the hose came off of to make sure it is not cracked, broken, or chipped. If the thermostat housing checks out good I would go to step 4
4. Make sure the thermostat housing is bolted down properly and the gasket is not pinched. If that checks out than go to step 5
5. Maybe replace the coolant hose with a BMW brand or just get a new hose all together.
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Old 02-09-2014, 06:24 PM   #5
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Did you torque the bolts correctly? That lower bolt will leak if you didn't.


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Old 02-09-2014, 06:28 PM   #6
thisisMikeNa
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Quote:
Originally Posted by 2003silver330i View Post
If it was my car I would do the following:

1. Try pushing the hose on with some force. If that doesn't do anything I would go to step 2
2. I would pull the coolant hose off and check o-ring on the inside and check the the outer plastic coupling for cracks. If those check out good than I would go to step 3
3. I would check around the thermostat opening that the hose came off of to make sure it is not cracked, broken, or chipped. If the thermostat housing checks out good I would go to step 4
4. Maybe replace the coolant hose with a BMW brand or just get a new hose all together.
Thanks! The hose I replaced the old one with is a BMW hose from the dealership and the o-ring and everything looks good. The new thermostat housing looks good too.

I can't pinpoint the leak exactly but when the car has been driven there's steam coming from that area of behind it.
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Old 02-09-2014, 06:32 PM   #7
2003silver330i
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Originally Posted by thisisMikeNa View Post
Thanks! The hose I replaced the old one with is a BMW hose from the dealership and the o-ring and everything looks good. The new thermostat housing looks good too.

I can't pinpoint the leak exactly but when the car has been driven there's steam coming from that area of behind it.
Sounds like you might have pinched the thermostat gasket when you installed it.
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Old 02-09-2014, 06:46 PM   #8
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You'll be able to see where it's leaking if you look up from underneath with a flashlight. Hose O ring, thermostat gasket, or even the sensor on the thermostat can leak.
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Old 02-09-2014, 07:38 PM   #9
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Check for leaks in other areas to be sure of the source.

On the expansion tank side the plastics can leak as well.




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Old 02-09-2014, 07:48 PM   #10
thisisMikeNa
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Thanks guys. I'm going to take everything out and carefully reinstall it (for the 3rd time).
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Old 02-09-2014, 07:50 PM   #11
thisisMikeNa
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Quote:
Originally Posted by swordsman11868 View Post
Check for leaks in other areas to be sure of the source.

On the expansion tank side the plastics can leak as well.




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The leak is coming from passenger side left of the thermostat housing. Hard to see exactly because it only leaks under pressure (steam), or when I've just come back from a drive at normal temp.
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Old 02-09-2014, 08:03 PM   #12
thisisMikeNa
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Originally Posted by rdogthenut View Post
Did you torque the bolts correctly? That lower bolt will leak if you didn't.


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I did not, what bolt needs to be torqued?
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Old 02-09-2014, 09:36 PM   #13
rdogthenut
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Just search thermostat diy. Torque bolts to 7ft pounds. It is a common leak after thermostat replacement.


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Old 02-09-2014, 09:50 PM   #14
thisisMikeNa
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I will try that tonight. Thanks a lot guys!
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Old 02-10-2014, 06:48 AM   #15
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Don't mean to hijack but...sort of related,

Does the thermostat gasket get coated with fresh coolant before installation or it is TStat installed dry?

Going to be doing my cooling system soon and this is one of my lingering questions.

Thanks,
CV
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