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E90/E91/E92/E93 (2006 - 2013)
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  #1  
Old 03-04-2013, 01:09 PM
bam bam is offline
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symptoms of thermostat failure

Can anybody tell me what the symptoms are of a thermostat failure? Curious to know as there seems to be some talk about the thermostat eveyr now and again. What I mostly read is that it fails open/closed. Can someone explain exactly what they means?
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  #2  
Old 03-04-2013, 02:44 PM
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floydarogers floydarogers is offline
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If your thermostat fails, the Service Engine Soon light will come on.

They're designed to fail open; this keeps coolant flowing. If they failed shut the engine would almost immediately overheat. In addition to the SES, if it does fail open, you won't have much heat from the heater.
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  #3  
Old 03-04-2013, 04:18 PM
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DSXMachina DSXMachina is offline
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Quote:
Originally Posted by floydarogers View Post
If your thermostat fails, the Service Engine Soon light will come on.

They're designed to fail open; this keeps coolant flowing. If they failed shut the engine would almost immediately overheat. In addition to the SES, if it does fail open, you won't have much heat from the heater.
Further to the OP's question, there are other things which are "failures" of a BMW thermostat. One of the more common ones is for the electrical resistance heater to burn or short out. Most stats open solely due to engine coolant temperature, but BMW will open theirs sooner and faster by heating them up with a signal from the PCM. That happens whenever the PCM weighs air temperature, coolant temperature, accelerator pedal position, and engine load and decides it needs to get the cooling show on the road right away. Then it zaps the stat, heats up the wax pellet which causes it to expand and force the stat to open.
Failure of that circuit wil usually set a thermostat specific code.
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  #4  
Old 03-24-2013, 08:10 AM
Daithi Daithi is offline
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Hi all.

I replaced the thermostat yesterday after the temp guage on the dashboard was at about 30%, running cold, Suggesting the thermo was stuck open, Also the heating inside the car wasnt great, further suggesting the same problem.

The temp guage went back to 50%, (12 o clock) which is normal and the heating returned to normal. Quite hot.

However, this only lasted for a while and now the problem of low heat inside the car and temp guage has returned to about 30%.

Does anyone have any experience of this oir any advice?

Note I only changed the main thermo.

Thanks in advance
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  #5  
Old 03-24-2013, 11:38 AM
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CALWATERBOY CALWATERBOY is offline
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Quote:
Originally Posted by Daithi View Post
....now the problem of low heat inside the car and temp guage has returned to about 30%.

Does anyone have any experience of this oir any advice?

Note I only changed the main thermo.

What codes are in memory?
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  #6  
Old 03-24-2013, 11:48 AM
Daithi Daithi is offline
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two codes showed up in memory. But Im told they were to do with a sensor for the air bag. I think one of them was a code 51? does this make any sense?
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  #7  
Old 03-24-2013, 12:00 PM
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CALWATERBOY CALWATERBOY is offline
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Originally Posted by Daithi View Post
two codes showed up in memory. But Im told they were to do with a sensor for the air bag. I think one of them was a code 51? does this make any sense?

No....ask for a complete readout including hidden & shadow codes.

Alternatively
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  #8  
Old 12-31-2016, 12:20 PM
rbelton rbelton is offline
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Agree with the comments above, they typically fail open and that makes it take forever to reach operating temp. It takes a healthy 3.0L M54 about 7-8 min to warm up in winter and almost 20 min to warm up with a failed thermostat. You may or may not have a P0128 code for thermostat failure. Here's a quick video of our test between two 3.0L M54 engines warm up times:



These conditions can lead to poor fuel mileage and additional wear on other components due to running rich.
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  #9  
Old 12-31-2016, 03:28 PM
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Zooks527 Zooks527 is online now
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Quote:
Originally Posted by rbelton View Post
Agree with the comments above, they typically fail open and that makes it take forever to reach operating temp. It takes a healthy 3.0L M54 about 7-8 min to warm up in winter and almost 20 min to warm up with a failed thermostat. You may or may not have a P0128 code for thermostat failure. Here's a quick video of our test between two 3.0L M54 engines warm up times:
The problem with comparing an E39 M54 with the N52/N54/N55 engines in the E90 series is that none of the E90s come with a water temperature gauge. Instead, they come with either a fuel efficiency gauge or an oil temperature gauge (all 335 models and coupes/convertibles). For those cars with an oil temperature gauge, it takes the better part of 20 miles of cold weather driving before the gauge will show that they're fully warmed up.
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  #10  
Old 01-01-2017, 07:12 AM
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07335 07335 is offline
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That failed in my 2007 at 80k miles. CEL on and code that pointed to the failed thermostat. It fails open so the car runs cooler.
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  #11  
Old 01-01-2017, 11:04 PM
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sptt144 sptt144 is offline
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Quote:
Originally Posted by Daithi View Post
Hi all.

I replaced the thermostat yesterday after the temp guage on the dashboard was at about 30%, running cold, Suggesting the thermo was stuck open, Also the heating inside the car wasnt great, further suggesting the same problem.

The temp guage went back to 50%, (12 o clock) which is normal and the heating returned to normal. Quite hot.

However, this only lasted for a while and now the problem of low heat inside the car and temp guage has returned to about 30%.

Does anyone have any experience of this oir any advice?

Note I only changed the main thermo.

Thanks in advance
Assuming that waterpump executed the bleed procedure ok for you after install?
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  #12  
Old 01-01-2017, 11:12 PM
Autoputzer Autoputzer is online now
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Mine was getting weak in my E46 M3... longer to warm up, lower water temperature at speed. I only popped a code once, on a cold morning creeping a half-mile through my 'hood at 15 MPH and then a mile my town for another mile at 30 MPH to let my 10W-60 engine oil get warm before I headed out on the highway. The code translated to something like "Excessive warm-up time" or something.

Last edited by Autoputzer; 01-01-2017 at 11:13 PM.
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  #13  
Old 01-02-2017, 02:58 AM
aleks001 aleks001 is offline
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I have a 06 325i N52.

I can confirm that when the thermostat fails that it will NOT display any check engine lights or other codes on the dashboard and the only way to know for sure is to scan with a tool that can read BMW codes.

Symtoms:
Car takes too long to warm up. Now how do you know if you are having this problem if you have an e90 since there is no temperature gauge?
The simplest way is to look how long it takes for the rpm to settle to around 600rpm, idle speed from a cold start.

The answer for an e90 is under a minute, I haven't timed it but it should be quite quick. If your car is not idling at 600 after 30 seconds to a minute it is most likely that your thermostat has failed and when they fail they fail open.

I'm not sure about all these other people reporting Check engine lights maybe they fixed it in newer models to alert you, but in mine there was definitely nothing, just took too long to settle to idle and because these cars have an electric water pump they tend to reach operating temperature very quickly and should be at normal idle speed I would say easily in 30 seconds to a minute maximum.

If you haven't replaced your water pump and are over or around 60K mark you might as well do it at the same time as it will save you a lot on labour and water pumps are pretty cheap these days I've seen them going for around $250 from Pierburg.
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  #14  
Old 01-02-2017, 06:47 AM
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NoQuarter NoQuarter is offline
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I don't think the idle speed dropping down in about 1 minute is related to the water temp.

The cold start cycle is a process of the ECU programming and has a specific time period Not a water temp period. Maybe it has both but I don't think so.

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  #15  
Old 01-02-2017, 04:59 PM
aleks001 aleks001 is offline
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Quote:
Originally Posted by NoQuarter View Post
I don't think the idle speed dropping down in about 1 minute is related to the water temp.

The cold start cycle is a process of the ECU programming and has a specific time period Not a water temp period. Maybe it has both but I don't think so.

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It's not related to the water pump it's related the thermostat. If the car can't warm up to operating temperature idle won't drop to 600 RPM.

I only mention the water pump to save the poster money if he has to replace the thermostat anyway as the water pump in these are not the longest lasting.
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  #16  
Old 01-02-2017, 05:45 PM
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NoQuarter NoQuarter is offline
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I get it... But the car does not come up to operating temp that fast. I still don't think the water raises temp enough for the ECU to detect it then lower the idle speed.

We are in agreement on changing pumps and thermostats. Just not how cold start idle speed is related to water temp.

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  #17  
Old 01-02-2017, 06:35 PM
aleks001 aleks001 is offline
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Quote:
Originally Posted by NoQuarter View Post
I get it... But the car does not come up to operating temp that fast. I still don't think the water raises temp enough for the ECU to detect it then lower the idle speed.

We are in agreement on changing pumps and thermostats. Just not how cold start idle speed is related to water temp.

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I can't really comment about all cars, just my own and the experience I had with a failed thermostat. That does not mean it will apply to the OP.

Also remeber im in Australia and the outsite temperature here never drops bellow 20 degrees/68 Fahrenheit so that could be a factor in the warm up time as well. But mine definitely post thermostat will settle to 600RPM under a minute.

When my thermostat failed it took a couple of minutes of driving before it settled.
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  #18  
Old 01-03-2017, 04:04 PM
aleks001 aleks001 is offline
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This morning I had a bit of a rough calculation and it definetly takes longer to for idle to settle than a minute, probably closer to the 2 minute mark.
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