GLK P0128
Thread Starter
Junior Member
Joined: Jan 2017
Posts: 16
Likes: 1
Mercedes GLK 2010
GLK P0128
Hi all!
Check engine light yesterday while driving. I scanned it with my basic OBDII tool and I got a P0128 code which means coolant thermostat is mostly bad. I've resetted it and drove about 75km since, and the light did not reappear.
I got a couple of questions. Should I wait for the light to be on again before fixing anything? I've seen thermostat online from 40$ to 200$ but I'm worried to order the wrong piece as I'm not perfectly bilingual (I speak french). It seems to be the "coolant thermostat". Is there more than one type of thermostat? do I need more stuff (extra coolant of course) but anything else needed? From what I've seen it's an easy diy that I would like to attempt.
I've seen several DIY for this piece for a X204 but none for the GLK precisely. someone have a link to a GLK DIY?
Thanks a lot everyone for the usual help
Check engine light yesterday while driving. I scanned it with my basic OBDII tool and I got a P0128 code which means coolant thermostat is mostly bad. I've resetted it and drove about 75km since, and the light did not reappear.
I got a couple of questions. Should I wait for the light to be on again before fixing anything? I've seen thermostat online from 40$ to 200$ but I'm worried to order the wrong piece as I'm not perfectly bilingual (I speak french). It seems to be the "coolant thermostat". Is there more than one type of thermostat? do I need more stuff (extra coolant of course) but anything else needed? From what I've seen it's an easy diy that I would like to attempt.
I've seen several DIY for this piece for a X204 but none for the GLK precisely. someone have a link to a GLK DIY?
Thanks a lot everyone for the usual help
Senior Member
Joined: Nov 2012
Posts: 379
Likes: 41
From: Jersey Shore
2012 GLK
What is your engine temp doing? i would take care of this in short order. Running too cold isnt good. It is an easy repair.
When i had this code the water temp never came above the bottom 1/8th. here is a post i made after doing the job
https://mbworld.org/forums/c-class-w...ml#post7261581
having done this today, i checked a few videos by several people. the best one i found was from FCP Euro, the other videos were a bit of a hack.
few tips...
expect to lose one gallon of coolant (yes i measured). i cut off the top of an old milk container and it helped catch 95% of it. i blew into the upper radiator hose to help force extra coolant out of thermostat. I then used baster method to suck out what i could from thermostat where it kept re-filling. Even after doing all that, you will still spill about a cup of coolant once the thermostat pops free. most of it can be contained if you are ready. I stuffed a lot of "pig mat" below it and it helped buy some time to control the flow. i did not want it getting on the pulleys. where it did, i wiped the pulleys down with alcohol and dried them off with compressed air. stuff a lint free rag to plug engine block, and clean gasket surface.
the plug: do not just pry up on the small gray tab on the plug as the video shows you. use a pick, gently lift on the black U tab on the middle of the plug, THEN slide the gray tab up. squeeze again (secondary lock) and it will release.
route the belt and install the belt on the tensioner last, very easy.
FCP shows them "purging the air" from the system by turning the heat on high and leaving the cover off the coolant reservoir tank while the vehicle is running. this will work initially to replace about a half gallon. after that's done, put the heat on full blast, CLOSE THE LID, and wait about 5-10 min. it will suck down the tank. you can open the lid the pour the other half gallon in. if you feel more comfortable turn the car off.
i left the lid off and was under the car installing the panel covers and the tank overflowed because im a dumbass.
some videos show guys doing this on the M272 without removing the air pump, or idler pulley... removing these takes two minutes and gives you a lot of room, making the job a breeze.
the job takes less than 2 hours working a snail pace while obsessively cleaning. I reset the P0128 code while the engine was running and wrapped up.
also a typo in above post by atlas: upper idler pulley is grooved #6, #3 is smooth. my upper pulley was failed, wish i had ordered at the same time. The smooth lower idler will have to come off to help get straight access to lower bolt on thermostat.
Tensioner bolt= 35Nm
Guide pully= 25Nm
Thermostat= 25Nm
https://youtu.be/jMmcEMuXayM
When i had this code the water temp never came above the bottom 1/8th. here is a post i made after doing the job
https://mbworld.org/forums/c-class-w...ml#post7261581
having done this today, i checked a few videos by several people. the best one i found was from FCP Euro, the other videos were a bit of a hack.
few tips...
expect to lose one gallon of coolant (yes i measured). i cut off the top of an old milk container and it helped catch 95% of it. i blew into the upper radiator hose to help force extra coolant out of thermostat. I then used baster method to suck out what i could from thermostat where it kept re-filling. Even after doing all that, you will still spill about a cup of coolant once the thermostat pops free. most of it can be contained if you are ready. I stuffed a lot of "pig mat" below it and it helped buy some time to control the flow. i did not want it getting on the pulleys. where it did, i wiped the pulleys down with alcohol and dried them off with compressed air. stuff a lint free rag to plug engine block, and clean gasket surface.
the plug: do not just pry up on the small gray tab on the plug as the video shows you. use a pick, gently lift on the black U tab on the middle of the plug, THEN slide the gray tab up. squeeze again (secondary lock) and it will release.
route the belt and install the belt on the tensioner last, very easy.
FCP shows them "purging the air" from the system by turning the heat on high and leaving the cover off the coolant reservoir tank while the vehicle is running. this will work initially to replace about a half gallon. after that's done, put the heat on full blast, CLOSE THE LID, and wait about 5-10 min. it will suck down the tank. you can open the lid the pour the other half gallon in. if you feel more comfortable turn the car off.
i left the lid off and was under the car installing the panel covers and the tank overflowed because im a dumbass.
some videos show guys doing this on the M272 without removing the air pump, or idler pulley... removing these takes two minutes and gives you a lot of room, making the job a breeze.
the job takes less than 2 hours working a snail pace while obsessively cleaning. I reset the P0128 code while the engine was running and wrapped up.
also a typo in above post by atlas: upper idler pulley is grooved #6, #3 is smooth. my upper pulley was failed, wish i had ordered at the same time. The smooth lower idler will have to come off to help get straight access to lower bolt on thermostat.
Tensioner bolt= 35Nm
Guide pully= 25Nm
Thermostat= 25Nm
https://youtu.be/jMmcEMuXayM
Newbie
Joined: Jun 2011
Posts: 8
Likes: 1
ML350
P0128 w164
Sorry for a slight off topic but does a P0128 code immediately mean that its a bad thermostat. And does it have to be replaced? Could it be a sensor issue?
As an FYI, have the same code pop up but temperature comes up fine and holds around 80 degrees. Everything seems to be working fine.
As an FYI, have the same code pop up but temperature comes up fine and holds around 80 degrees. Everything seems to be working fine.
Last edited by cgold79; Nov 26, 2018 at 09:36 AM. Reason: additional info
MBWorld Fanatic!
Joined: Sep 2015
Posts: 2,585
Likes: 343
2013 glk 350
Get a genuine mb thermostat, best might be a mb dealership. Running a thermostat that doesn’t close and allows the motor to run cool will mess up your motor fast , it will not allow the oil to reach proper temperature fast enough to cook out contaminants , it will encourage sludge build up, I don’t know how your thermostat is actually operating, if it’s slow to warm or never does. But running a cold motor it a quick way to ruin a motor. Change your oil also since this is what gets contaminated. I wouldn’t trust a non mb thermostat , but it shouldn’t cost more than 40$, 200 is crazy just for the thermostat itself and no install.
I’m familiar with running a cold motor , I just about ruined mine and also had to replace the crancake ventilation components at a big cost because it sludged up from running cold. But is yours running cold? Or taking long to warm ? Figure it out quickly.
I’m familiar with running a cold motor , I just about ruined mine and also had to replace the crancake ventilation components at a big cost because it sludged up from running cold. But is yours running cold? Or taking long to warm ? Figure it out quickly.
Thread Starter
Junior Member
Joined: Jan 2017
Posts: 16
Likes: 1
Mercedes GLK 2010
since I've reset the check engine light (600km ago) light never came back on. so now i'm confused, should I change the thermostat even if the CEL does not light again?
at the moment the temperature is at middle which is exactly where it used to be.
at the moment the temperature is at middle which is exactly where it used to be.
Senior Member
Joined: Nov 2012
Posts: 379
Likes: 41
From: Jersey Shore
2012 GLK
give it a few weeks, it will likely come back.
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MBWorld Fanatic!
Joined: Sep 2015
Posts: 2,585
Likes: 343
2013 glk 350
The last post was sent by mistake before I finished, what temp do you settle at after 10 minutes and what’s your outside temp. I get to 83c in about 8 minutes at 32f, quicker on the highway. If your much below 83c or it fluctuates or it takes much longer then yes its probably bad. I think 83c is where it needs to be, not 80c, and saying middle of the gauge is meaningless.
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MBWorld Fanatic!
Joined: Sep 2015
Posts: 2,585
Likes: 343
2013 glk 350
Tomorrow morning see how many minutes it takes to get to the highest temp, if it’s like 10 minutes to 83 it might be ok, if it takes 15-20 or it’s at 78 after 15 minutes it could be bad. It needs to get to 82-83, the faster the better.
MBWorld Fanatic!
Joined: Sep 2015
Posts: 2,585
Likes: 343
2013 glk 350
I’m wrong on the temp, the second line above 80 is 90c and today I got to 91c in 12 minutes at 23f outside- Chicago . If your glk is in a heated garage it might only take 5-7 minutes, 91c is 195.8 , I think I’m ok.
