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  #101  
Old 10-29-2015, 10:29 AM
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Thanks for confirming the value stamped on the stat. This can often be misleading because SO MANY people think the engine is supposed to operate at the stat temp which is RARELY the case. Except for M vehicles, most engines operate in the 205F/96C range. When the engine runs cool, fuel consumption increases and oil contaminates quicker.
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  #102  
Old 10-29-2015, 10:54 AM
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I ordered the main thermostat from AutohausAZ and the transmission cooler thermostat with GetBMWParts. AutohausAZ doesn't carry the transmission cooler thermostat. I will check the temps today more thoroughly as yesterday after the wife came home I checked the temp and it never went up above 72 and played between 68 and maxed out at 72.

Has anyone had this thermostat fail the opposite way (completely shut)? This seems to be the issues we deal with in the gas engines. I have had a number of cars have this issue but never running colder than spec.
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  #103  
Old 10-29-2015, 11:16 AM
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Most modern thermostats go soft and run too cold. The main springs get weak over time, sometimes in less than 2 years.

Get OBDFusion for your phone/tablet and the proper interface (usually less than $20) and you can easily monitor AND Log the temps and other values.
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  #104  
Old 10-29-2015, 11:19 AM
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Quote:
Originally Posted by RIHI View Post
I ordered the main thermostat from AutohausAZ and the transmission cooler thermostat with GetBMWParts. AutohausAZ doesn't carry the transmission cooler thermostat. I will check the temps today more thoroughly as yesterday after the wife came home I checked the temp and it never went up above 72 and played between 68 and maxed out at 72.

Has anyone had this thermostat fail the opposite way (completely shut)? This seems to be the issues we deal with in the gas engines. I have had a number of cars have this issue but never running colder than spec.
Don't forget that there is (dependant on engine) an EGR cooler stat too and that can fail
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  #105  
Old 10-29-2015, 01:04 PM
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Quote:
Originally Posted by jfoj View Post
Most modern thermostats go soft and run too cold. The main springs get weak over time, sometimes in less than 2 years.

Get OBDFusion for your phone/tablet and the proper interface (usually less than $20) and you can easily monitor AND Log the temps and other values.
I understand in this particular instance the spring is not strong enough to close the flow. I am understanding the meaning of a "modern" thermostat as the issue of a failed thermostat in a gas engine is commonplace even at this time. I have an 08 535xi wagon where I just replaced the thermostat for that very reason.
My question was, are there folks who have had issues with a closed thermostat that leads to overheating?
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  #106  
Old 10-29-2015, 01:09 PM
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I finally got to monitor the coolant temperature in the X5 this morning. The run to wife's office with the AC on at 16 deg C outside temperature never went above 72 deg C.

On my way to my office, I turned off the AC and the highest the temp got was while I was idling for a few minutes at a stoplight. It went up to 84 deg C but went down after the stop light and settled at around 72 deg C on the freeway.

With my wife driving, it never left 72 deg and would go back and forth between 68 to 72. So definitely needing a thermostat replacement.

It's a good thing, I have placed the order for the two thermostats.
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  #107  
Old 10-29-2015, 01:13 PM
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Quote:
Originally Posted by RIHI View Post
I understand in this particular instance the spring is not strong enough to close the flow. I am understanding the meaning of a "modern" thermostat as the issue of a failed thermostat in a gas engine is commonplace even at this time. I have an 08 535xi wagon where I just replaced the thermostat for that very reason.
My question was, are there folks who have had issues with a closed thermostat that leads to overheating?
The problem is not that the spring is not strong enough to close the thermostat properly, the problem is the preload on the spring is not strong enough therefore allowing the thermostat to start to open too early.

As for thermostats stuck closed, it rarely happens based on the design. Most overheating problems these days are due to low coolant/coolant leaks. Low coolant can cause the thermostat to not open due to no warm coolant for the thermostat to react to.
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Last edited by jfoj; 11-01-2015 at 09:15 AM.
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  #108  
Old 11-21-2015, 11:11 PM
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Finally got around to replacing the thermostats. I followed the advise here and replaced both the radiator and oil cooler thermostats. After going around 3 miles the temperature now reads 87 degrees.
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  #109  
Old 11-25-2015, 11:03 AM
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I'm wondering what the consensus is on what exactly constitutes a 'bad' thermostat. I monitored the coolant temps on my wife's X5 while towing a trailer in a mix of city and highway driving, with outdoor temps at 40F. The temps were pretty consistent between 79 -82C...certainly not as low as some here are experiencing. I have a new thermostat on the way and I'll probably install it anyway just to get ahead of when the original unit does eventually fail, but I'm almost thinking that it might be OK for now.
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  #110  
Old 11-25-2015, 01:24 PM
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You are getting to 82 because you are towing. The only time I got there was when I turned off the AC which turns off the fan (until it needs it) and I ws idling for a couple of minutes at a stop light. After which it went back to 72.

As mentioned in previous posts, if the thermostat doesn't keep the temp at 88 or so degrees, the glow plugs turn on to keep it at that temperature and the DPF does not regenerate. If this continues, the glow plugs will eventually burn itself out and the DPF will clog.

The worst issue with a thermostat is if fails at the closed position making the car overheat. This was the question, I was asking earlier, Has anyone had a thermostat fail in the closed position and having overheated the motor?

Either way, both issues require attention.
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