Did anyone have a faulty thermostat on K12LT? - BMW Luxury Touring Community
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post #1 of 27 Old Nov 24th, 2015, 8:15 am Thread Starter
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Question Did anyone have a faulty thermostat on K12LT?

Hello everybody

My LT is a 2006 model and shows 90000 km (~55000 miles) on the odometer.
Since last summer, the engine temperature is not as stable as it was before, but it does not actually overheat.
The fans work OK when necessary and the gauge did never approach the upper limit nor did the warning light come on.
I was thinking that the cause could be a sticky thermostat.
Reading previous posts it appears that changing the thermostat on K bikes is not that easy.
So before beginning such a task, and maybe making things worse, I would like to know if anyone had experienced a faulty thermostat on a K12 LT or other K bike.

Thanks in advance

Bruno

Bruno_C
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post #2 of 27 Old Nov 24th, 2015, 9:33 am
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Re: Did anyone have a faulty thermostat on K12LT?

I have about 200,000 miles riding my two LT's & have never had a thermostat problem.
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post #3 of 27 Old Nov 24th, 2015, 10:13 am
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Re: Did anyone have a faulty thermostat on K12LT?

Sounds normal to me.
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post #4 of 27 Old Nov 24th, 2015, 10:25 am Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

Thank you for these first replies.
I keep waiting for more advice.

Best regards

Bruno

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post #5 of 27 Old Nov 24th, 2015, 11:01 am
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Re: Did anyone have a faulty thermostat on K12LT?

The LT does go up real close to the red mark before the fan comes on its pretty much normal

Gary
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post #6 of 27 Old Nov 24th, 2015, 11:47 am
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Re: Did anyone have a faulty thermostat on K12LT?

I didn't have a problem with the t-stat, but I DID have a problem with the Radiator cap (my bike's got about the same mileage yours does.)

It was painful, but I managed to replace the stocker for the replacement without pulling the panels off.

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post #7 of 27 Old Nov 24th, 2015, 3:55 pm
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Re: Did anyone have a faulty thermostat on K12LT?

To help with diagnosis there are a couple of checks that can be done, they require some previous history or knowlwdge of the 'normal' behavior. Firstly, the thermostat is essentually a temperature regulator - it responds to varying engine loads by quickly varying it's opening position in order to maintain a constant colant temperature. So from a cold start, and taking into account the actual ambient temperature, the engine should reach operating temperature in the same time each time. If this becomes variable, normally it will become longer, then the thermostat is likely to be not completely closing when cold. The second observation needs to be done when the engine is at operating temperature. Observe the temperature gauge during an extended downhill run when load on the engine is low. The temperature should hold in the normal position on the gauge. If it drops then it is possible the thermostat is sluggish to close. Apart from these possibilities, it may be that the temperature sender is faulty but others (maybe Sailor) can better advise on known resistance values for the unit at differing temperatures. Hope this helps.

Dennis
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post #8 of 27 Old Nov 24th, 2015, 4:24 pm
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Re: Did anyone have a faulty thermostat on K12LT?

Of course you checked if you have any air bubbles trapped in your radiators and these are not completely filled up.
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post #9 of 27 Old Nov 24th, 2015, 9:27 pm
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Re: Did anyone have a faulty thermostat on K12LT?

The LT has 2 engine temperature sensors, one in the coolant stream near the water pump, and one on the head. If the one located in the head goes bad, your indications would be that the cooling fans will come on when the temperature gauge is still below the red level, in my case well below the red level. I guess the temp gauge is regulated by the sender near the coolant pump and the cooling fans are regulated by the sender in the head. It also sends temp info to the bikes computer. don't know if this might be helpful to you or not..

RICH CANNON
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post #10 of 27 Old Nov 25th, 2015, 2:30 am Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

I would like to answer to K100Dennys:
Previously the needle of the temp gauge used to be very steady at the midpoint of the scale. Now it has become more variable, 3 or 4 mm above the midpoint in the climbs and 3 or 4 mm downhill.
So I suspect the thermostat becoming sluggish.
At this point it is not a problem and I could leave it alone but I fear it could become stuck closed one day during a ride with unpleasant consequences.
I know that thermostats can stick closed. It happened to my car a few years ago.
But K1200 thermo is very different that is why I asked if someone actually experienced a stuck closed thermostat on a K bike.

Bruno

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post #11 of 27 Old Nov 25th, 2015, 12:35 pm
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Re: Did anyone have a faulty thermostat on K12LT?

Bruno, you aware of how the engine temperature behaved previously and I am making an assumption that you have not changed the coolant recently, right ? If this is the case, then I would be looking to replace the thermostat unit. At the end of the day they are a mass produced device and normally very reliable, but as you know, some will fail early in service and you may be the unlucky one here. Please keep us informed of the outcome.

Dennis
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post #12 of 27 Old Nov 25th, 2015, 2:22 pm
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Re: Did anyone have a faulty thermostat on K12LT?

Keep in mind the Radiator cap is 9 years old, is relatively cheap and relatively easy to replace. My bike had overheating issues at a stop...you could watch the needle creep up til you felt uncomfortable with how high it was getting. If you held the engine to 2000 rpm or so, the temp would fall, and if you held your hand over the radiator exhausts, you'd feel the air getting SUBSTANTIALLY hotter than when it was sitting at idle.

Water based cooling system MUST create and maintain higher than atmospheric pressure to operate, if that cap isn't allowing the system to pressurize, your coolant will be losing a LOT of efficiency.

In my case (see attached) the rubber gasket looks....compromised.

Raplacing the Cap dramatically improved the performance of my cooling system. I cannot say it's fixed it 100%, because I didn't really notice the behavior until the system was very broken.

The worst thing that can happen is: Hey, you have a new radiator cap installed...that's not a bad thing. The best thing that can happen is you keep from having to SERIOUSLY disassemble your bike.
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post #13 of 27 Old Nov 26th, 2015, 3:29 am Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

Hi,
for the moment nobody reported an actual thermostat failure.
Maybe this winter I will only change the fluid and the cap because this way it can make no harm.
Then I will see if it makes a difference and if necessary I will change the thermostat.

Have a good day

Bruno
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post #14 of 27 Old Nov 26th, 2015, 7:53 am
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Re: Did anyone have a faulty thermostat on K12LT?

Bruno,

The post I did a while back while diagnosing my system may be of help to you. It includes photos of all the offending parts. I thought I had a failed thermostat and found the primary problem was with the radiator cap, however there was also the matter of matter stuck in the radiators that I suspect most owners don't notice.

http://www.bmwlt.com/forums/k1200lt/...ting-info.html

Steve
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post #15 of 27 Old Nov 26th, 2015, 10:42 am Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

Steve
I know your post.
It shows that the thermostat is not that easy to change.
That is why I hesitate...

Thanks again

Bruno

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post #16 of 27 Old Nov 27th, 2015, 6:36 pm
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Re: Did anyone have a faulty thermostat on K12LT?

Bruno,

Replacing the thermostat is a little challenging, mostly need lots of patience. If you decide to swap your radiator cap, please have the old one tested for pressure and let us know what you find. Of those I have talked to with bad caps, three of us have found the caps holding too much pressure and one has found too little. A little confusing how they fail but changing them out does make a difference. When you go to put a new cap on, make sure you lube the rubber seal either with antifreeze or something slicker than plain water, it will definitely make it easier to get the cap turned all the way closed and back off again as you burp the system.

Steve
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post #17 of 27 Old Mar 14th, 2016, 8:01 pm
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Re: Did anyone have a faulty thermostat on K12LT?

Quote:
Originally Posted by GaryEm View Post
The LT does go up real close to the red mark before the fan comes on its pretty much normal

Just what I needed to read. Thank you!

Jerry


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post #18 of 27 Old Dec 3rd, 2016, 12:05 pm Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

Hello everybody

After a few months of hesitation I took advantage of the winter maintenance of the bike to give a look to the thermostat.
I was surprised to find that it was broken.
More precisely, the plastic part that keeps together the spring and the thermostatic capsule was broken.

The thermostat worked all the same and I was able to do a 4000 km tour this summer with no significant trouble. But the regulation of the température was not as accurate as it was in the past and, for peace of mind, I decided to give it a look.

After refilling the cooling circuit, I rode a few miles. The temp dial seems to be very steady now.

Bruno
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post #19 of 27 Old Dec 3rd, 2016, 2:25 pm
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Re: Did anyone have a faulty thermostat on K12LT?

Quote:
Originally Posted by bruno_c View Post
Hello everybody

After a few months of hesitation I took advantage of the winter maintenance of the bike to give a look to the thermostat.
I was surprised to find that it was broken.
More precisely, the plastic part that keeps together the spring and the thermostatic capsule was broken.

The thermostat worked all the same and I was able to do a 4000 km tour this summer with no significant trouble. But the regulation of the température was not as accurate as it was in the past and, for peace of mind, I decided to give it a look.

After refilling the cooling circuit, I rode a few miles. The temp dial seems to be very steady now.

Bruno
Bruno, thank you for the update.
Would you have any photos of your broken thermostat?? I am curious to see a close-up of this...
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post #20 of 27 Old Dec 4th, 2016, 11:13 am Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

This is my first attempt to attach a picuture to my reply.
Not sure of the result.

Anyway, the thermostat assembly of the K bikes is made of a thermostatic capsule and a spring held together by a plastic assembly.
On the picture, you see a plastic part. it should have four hooks but two were broken. I found only one. The other one was propelled by the spring across the shed.
Have a good evening

Bruno
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post #21 of 27 Old Dec 4th, 2016, 11:20 am
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Re: Did anyone have a faulty thermostat on K12LT?

Quote:
Originally Posted by bruno_c View Post
Anyway, the thermostat assembly of the K bikes is made of a thermostatic capsule and a spring held together by a plastic assembly.
Thanks for sharing. We do not see many thermostat failures on our bikes.

Mike Trevelino
Williamsburg, VA
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post #22 of 27 Old Dec 4th, 2016, 12:39 pm Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

A friend of mine with a BMW K100 had also a thermostat failure a few years ago.
I think the thermostat is the same as on the K1200
Butthis freind was not as lucky as me because his thermostat stuck closed during a summer ride in South Italy and Greece;
He had to have it fixed immediately.

Bruno

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post #23 of 27 Old Dec 4th, 2016, 2:18 pm
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Re: Did anyone have a faulty thermostat on K12LT?

Quote:
Originally Posted by bruno_c View Post
This is my first attempt to attach a picuture to my reply.
Not sure of the result.

Anyway, the thermostat assembly of the K bikes is made of a thermostatic capsule and a spring held together by a plastic assembly.
On the picture, you see a plastic part. it should have four hooks but two were broken. I found only one. The other one was propelled by the spring across the shed.
Have a good evening

Bruno
Bruno,
Thanks you for taking time to post this picture. To me, it looks like it was forced / broken during last installation - maybe by previous owner or mechanic. This kind of failure is not common on K1200 "brick-engine". They are a bit tricky to install / push fully in place....

For those that would like to see what these look like (when not broken), see last 3 photos at bottom of this older post here:
http://www.bmwlt.com/forums/k1200lt/...ml#post1312810

Although they are also "brick-engine" earlier K100 and K75 are different animals with a single large radiator. The thermostat is larger and more accessible like many cars. See attached photo...
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K1200RS (2002 IceBlue/Red - 96,000 miles)
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Last edited by sailor; Dec 4th, 2016 at 2:28 pm.
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post #24 of 27 Old Dec 5th, 2016, 3:45 am Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

In fact the thermosatat has never been touched since the bike was new.
Maybe mine is the only one known to have failed in service.

Concerning the difficulty to undo and to install, I have been surprised to find it pretty easy.
It is important to use a bit of heatgun on the housing and to to put the capsule in the freezer before fitting.

Bruno

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Norton Commando 1976

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post #25 of 27 Old Dec 5th, 2016, 6:42 am
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Re: Did anyone have a faulty thermostat on K12LT?

Quote:
Originally Posted by bruno_c View Post
It is important to use a bit of heatgun on the housing and to to put the capsule in the freezer before fitting.
Oh yea, besides the heatgun and freezer, a piece of cake! (LOL)

Mike Trevelino
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post #26 of 27 Old Dec 5th, 2016, 10:29 am
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Re: Did anyone have a faulty thermostat on K12LT?

Quote:
Originally Posted by bruno_c View Post
In fact the thermosatat has never been touched since the bike was new.
Maybe mine is the only one known to have failed in service.

Concerning the difficulty to undo and to install, I have been surprised to find it pretty easy.
It is important to use a bit of heatgun on the housing and to to put the capsule in the freezer before fitting.

Bruno
Freezer? Seriously? Only BMW would require you to freeze a thermostat before installation.
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post #27 of 27 Old Dec 5th, 2016, 10:45 am Thread Starter
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Re: Did anyone have a faulty thermostat on K12LT?

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Freezer? Seriously? Only BMW would require you to freeze a thermostat before installation.
It seems a bit strange to put the thermostat in the freezer but it is the normal process as described in the Clymer manual and also in Steve Green's post.
Good evening

Bruno

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