# thermostat and DPF regeneration



## Michael47 (May 9, 2014)

So for the last 18 months or so, I've noted my coolant temperature has been below the 82°C-89°C called out as normal. Generally as I drove around it would run 78° to 80°C, and having noted the thread elsewhere about the risks of damage to the expensive DPF if the cold engine prevented a regen cycle, I've been watching it closely, and noting that regeneration cycles continued to happen about once every tank of diesel. Last week, as the temperatures here in the east started to get cold, I noticed that I was seeing a lot of 73°-74°C, which suggested that the time was at hand when I'd have to spring for the new thermostat, and I made the appointment with my friendly Indy.

So this morning it hit 2°F here overnight, and I found myself headed out on an errand. Driving through town, I noted that coolant temperatures were running 63° or so, proof to me that the thermostat was toast. I got out on the expressway and a mile or so at highway speeds brought the temperature up to 73°C, and lo and behold, a regeneration cycle began. I went out of my way to stay at highway speeds until it completed. Wednesday the thermostat gets replaced.

But I wanted y'all to know that evidently a failed thermostat can trigger a regen provided you can get the coolant up to the mid 70s. Since the function of the thermostat is to keep operating temperature above a set minimum temperature, there's no doubt I need a new one. My Indy says the job takes 4.3 hours of labor, accounting for the lion's share of the $640 it's going to cost. Gone are the days when a $15 thermostat and two bolts requiring all of 15 minutes for the job was all it takes.


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## floydarogers (Oct 11, 2010)

Yeah, when the thermostat was replaced on my 335d, it cost quite a bit in labor. It's in a bad place...


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## Doug Huffman (Apr 25, 2015)

Michael47 said:


> Since the function of the thermostat is to keep operating temperature above a set minimum temperature,


... and below a maximum. Our thermostats' wax motor has farther travel open after its nominal operating temperature.


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## rbreding (Sep 6, 2016)

4.3 hrs? Holy crap. 15 minutes to remove the fan. 45 min to pull and replace the therm (max). 45 min to fill and purge coolant (max).

I think it took me an extra 30 minutes to add the therm replacement to my deletes.


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## Doug Huffman (Apr 25, 2015)

There is never time to do it right the first time but always money to do it over. What is the hurry?


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## edycol (Jul 8, 2015)

60c is necessary for regeneration. If coolant cannot reach 60c after some time, CEL will pop up. However, problem is when it drops below 75c, glow plugs will activate to help engine efficiency. You have to address this issue as glow plugs or control module might die. Regeneration should be ok. 


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## lawlknight (Sep 13, 2016)

I paid $88.90 for a new thermostat and 3.5 hours of labor to get it replaced.


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## Michael47 (May 9, 2014)

My indy wrench is replacing the thermostat per my request. He says until it sets a check engine light, it is considered still a good thermostat. However, as preventative maintenance, and being 88,000 miles old, he can't argue with the logic.


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## lawlknight (Sep 13, 2016)

Michael47 said:


> My indy wrench is replacing the thermostat per my request. He says until it sets a check engine light, it is considered still a good thermostat. However, as preventative maintenance, and being 88,000 miles old, he can't argue with the logic.


From what I understand, when they fail, they generally get stuck open. Meaning your engine won't get up to temperature. And for a diesel with a DPF regeneration cycle, it needs to get up to temperature. I'm not sure how it is there, but most places here don't have much experience with BMW diesels. The shop I go to gets 20 cars a day, and maybe 1 diesel a month (usually mine).


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## rbreding (Sep 6, 2016)

Michael47 said:


> My indy wrench is replacing the thermostat per my request. He says until it sets a check engine light, it is considered still a good thermostat. However, as preventative maintenance, and being 88,000 miles old, he can't argue with the logic.


Therm wont throw a CEL. However the symptoms will and by that time you will be several hundreds or thousands deeper down the hole. The glow plugs and controller will be stressed by a low temp engine. Regens will eventually stop due to low temp.

Temps should "virtually" always be above 85c (185f) when the engine is up to operating temp.

As an anecdotal note. My newly purchased '13 X5 with 52k miles showed 79c (174f) during its drive home. Replaced the therm during deletes and now she runs above 85c all the time. See attached pic for recently long highway drive in chilly Kansas.


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## edycol (Jul 8, 2015)

rbreding said:


> Therm wont throw a CEL. However the symptoms will and by that time you will be several hundreds or thousands deeper down the hole. The glow plugs and controller will be stressed by a low temp engine. Regens will eventually stop due to low temp.
> 
> Temps should "virtually" always be above 85c (185f) when the engine is up to operating temp.
> 
> As an anecdotal note. My newly purchased '13 X5 with 52k miles showed 79c (174f) during its drive home. Replaced the therm during deletes and now she runs above 85c all the time. See attached pic for recently long highway drive in chilly Kansas.


It will throw when ECU recognizes that engine has hard time staying above 60c. That is of course ridiculous.

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## rbreding (Sep 6, 2016)

edycol said:


> It will throw when ECU recognizes that engine has hard time staying above 60c. That is of course ridiculous.
> 
> Sent from my iPhone using Tapatalk


Maybe so. By that time Im betting no regens and other systems being stressed.

Let's call the therm a "maintenance" part.


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## edycol (Jul 8, 2015)

rbreding said:


> Maybe so. By that time Im betting no regens and other systems being stressed.
> 
> Let's call the therm a "maintenance" part.


I think it is long established that thermostat is maintenance item. DPF needs 60c to regenerate. However, if engine cannot get to 75c glove plugs will activate. That is problem.

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## rbreding (Sep 6, 2016)

edycol said:


> I think it is long established that thermostat is maintenance item. DPF needs 60c to regenerate. However, if engine cannot get to 75c glove plugs will activate. That is problem.
> 
> Sent from my iPhone using Tapatalk


Yep. Definately an issue with the glow plugs. More costs.... Which was my point.


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## Michael47 (May 9, 2014)

Well, after saying that he'd replace it on my say-so, but he wouldn't guarantee it'd run any warmer in light of cold winter temperatures and all, when done, he took it for a drive and reported (surprise, surprise) that it was now running 85°C.


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## rbreding (Sep 6, 2016)

Michael47 said:


> Well, after saying that he'd replace it on my say-so, but he wouldn't guarantee it'd run any warmer in light of cold winter temperatures and all, when done, he took it for a drive and reported (surprise, surprise) that it was now running 85°C.


What is your ambient temps outside where you are at ? 85c is a good number


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## edycol (Jul 8, 2015)

Michael47 said:


> Well, after saying that he'd replace it on my say-so, but he wouldn't guarantee it'd run any warmer in light of cold winter temperatures and all, when done, he took it for a drive and reported (surprise, surprise) that it was now running 85°C.


Ambient temperature is irrelevant when it comes to maintenance of temperature. Low ambient temperature will delay warm up. I had 88c while ambient was -27. Granted it took awhile to get there.

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## Michael47 (May 9, 2014)

Quite so, @edycol. Evidently many people do not understand how auto engine thermostats are supposed to work. They are supposed to trap all heat possible until the engine reaches Official Operating Temperature***8482;, whatever that is. Then they are supposed to open up/release only enough heat to keep the engine at that temperature. Granted, we are not talking about 6 decimals worth of accuracy here, we're talking about a range, in this case 82°C to 89°C. Outside of ridiculous ambient temperatures, say -80°C for instance, or +100°C, the thermostat is designed to keep the engine locked down at those temperatures.

What's more, it is much easier to put a floor on the engine temperature than it is to put on a ceiling. Thus if you drag a maximum weight trailer (i.e., 6,000 lb) up a 15% slope in 120°F weather, don't be too surprised if the engine temperature rises above 89°C. That's why having a proper pressure-holding cap on the cooling system, and that filled with the right coolant, is important. The cooling system will get better and better at dissipating heat at higher operating temperatures, so it's ok for that to happen, within limits.

So I have no idea why the wrench working on the car would doubt the new thermostat would raise the operating temperature, regardless of the ambient temperature. If the old one lets the engine cool off to 61°C, when it's not so cold I've already frozen to death, it should be pretty clear it isn't doing its job.


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## Waysian (Mar 23, 2007)

rbreding said:


> Therm wont throw a CEL. However the symptoms will and by that time you will be several hundreds or thousands deeper down the hole. The glow plugs and controller will be stressed by a low temp engine. Regens will eventually stop due to low temp.
> 
> Temps should "virtually" always be above 85c (185f) when the engine is up to operating temp.
> 
> As an anecdotal note. My newly purchased '13 X5 with 52k miles showed 79c (174f) during its drive home. Replaced the therm during deletes and now she runs above 85c all the time. See attached pic for recently long highway drive in chilly Kansas.


What program are you using to measure your engine temperature? Is that an app?


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## Michael47 (May 9, 2014)

So, one more note on the new thermostat. Drove it through town yesterday at 21°F, and it held 85°C on the road, and fell to 83°C sitting at idle at a long light.


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