Coolant thermostat Stuck open
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Coolant thermostat Stuck open
So I've had this code P0128 for a few weeks now. Points to a failed thermostat (failed in stuck open).
I saw there are two ways to do this. One is to replace the thermostat and the housing and the other way is to replace just the thermostat.
Has anyone done the second one successfully? This video on youtube shows this method - seems a lot simpler to do for the issue at hand....are there any draw backs?
I saw there are two ways to do this. One is to replace the thermostat and the housing and the other way is to replace just the thermostat.
Has anyone done the second one successfully? This video on youtube shows this method - seems a lot simpler to do for the issue at hand....are there any draw backs?
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From: Jakarta-Indonesia
2014 - W212.065 - E400 ( M276.820, 3 liter Turbo) RWD not Hybrid
The engine shown is M276.8xx Turbo.
Anyway, replace the thermostat as a complete unit is best. They are plastic body, thus it will crack when old.... so all new is better.
There is actually another small plastic pipe which shares water output of both cylinder banks before going to that thermostat housing.
Read here : https://mbworld.org/forums/e-class-w...ot-2-them.html
If you intend to keep the car up to 20th year, I suggest your replace that small pipe.
Anyway, replace the thermostat as a complete unit is best. They are plastic body, thus it will crack when old.... so all new is better.
There is actually another small plastic pipe which shares water output of both cylinder banks before going to that thermostat housing.
Read here : https://mbworld.org/forums/e-class-w...ot-2-them.html
If you intend to keep the car up to 20th year, I suggest your replace that small pipe.
Out Of Control!!
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
This is really not bad. compared to V8 or working at the rear between engine/firewall: PCV & heater elbow.
It's best to group work campaigns together.
Tstat doesn't just go bad prematurely for no reason. Extreme heat causes it to get jammed.
It's best to group work campaigns together.
Tstat doesn't just go bad prematurely for no reason. Extreme heat causes it to get jammed.
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The car has never overheated, it just stuck open and runs fine. We just did a 1200mile trip on it, no issues. Half way the CEL even went away as we got to warmer states (im in NJ).
Is there a procedure document for how to get to the Tstat and this pipe in the back of it? It looks like I'll have to remove charge intercooler to remove the t-stat.
Out Of Control!!
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
The car has never overheated, it just stuck open and runs fine. We just did a 1200mile trip on it, no issues. Half way the CEL even went away as we got to warmer states (im in NJ).
Is there a procedure document for how to get to the Tstat and this pipe in the back of it? It looks like I'll have to remove charge intercooler to remove the t-stat.
Is there a procedure document for how to get to the Tstat and this pipe in the back of it? It looks like I'll have to remove charge intercooler to remove the t-stat.
WIS has a well detailed procedure for every service job !!
> The takeaway is to replace every seal and O-rings you disturb. Specifically O-rings :
-- the hottest coolant pipe that returns from oil heat exchanger.
-- The large pipe to radiator.
Drain/Renew radiator content: less than 1-gallon Zerex (YLW/BLU) formula.
Last edited by CaliBenzDriver; Apr 24, 2025 at 02:10 PM.
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It's interesting you say it failed when you got to warmer states. It lost its ability to open/close smoothly as commanded by ECU current.
WIS has a well detailed procedure for every service job !!
> The takeaway is to replace every seal and O-rings you disturb. Specifically O-rings :
-- the hottest coolant pipe that returns from oil heat exchanger.
-- The large pipe to radiator.
Drain/Renew radiator content: less than 1-gallon Zerex (YLW/BLU) formula.
WIS has a well detailed procedure for every service job !!
> The takeaway is to replace every seal and O-rings you disturb. Specifically O-rings :
-- the hottest coolant pipe that returns from oil heat exchanger.
-- The large pipe to radiator.
Drain/Renew radiator content: less than 1-gallon Zerex (YLW/BLU) formula.
Sorry I think I may have not stated it correctly! But the failure occurs only around NJ for now while its cold here in NJ. Over the weekend we were in the southern states and there was no issue - CEL went away and the temp gauge read midway as it always has. When we started our way up and got closer to NJ I saw that the temp gauge was running cooler than normal (stuck open) and CEL returned (P0128)
Just bought the WIS on ebay a few minutes ago. Looking forward to get this done.
Last edited by Dawgz; Apr 24, 2025 at 02:16 PM.
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Out Of Control!!
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
Sorry I think I may have not stated it correctly! But the failure occurs only around NJ for now while its cold here in NJ. Over the weekend we were in the southern states and there was no issue - CEL went away and the temp gauge read midway as it always has. When we started our way up and got closer to NJ I saw that the temp gauge was running cooler than normal (stuck open) and CEL returned (P0128)
Just bought the WIS on ebay a few minutes ago. Looking forward to get this done.
Just bought the WIS on ebay a few minutes ago. Looking forward to get this done.
Perhaps you've noticed routinely when driving out of town on Hwy : the Tstat overcools and temp gauge ends up too low.
Your engine has a "mapped temp control". It stores and release heat.
Last edited by CaliBenzDriver; Apr 24, 2025 at 02:30 PM.
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Thread Starter
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That's an interesting observation. You're saying overcooling in NJ ie. stuck more opened than needed.
Perhaps you've noticed routinely when driving out of town on Hwy : the Tstat overcools and temp gauge ends up too low.
Your engine has a "mapped temp control". It stores and release heat.
Perhaps you've noticed routinely when driving out of town on Hwy : the Tstat overcools and temp gauge ends up too low.
Your engine has a "mapped temp control". It stores and release heat.
Yes that's a better way to put it, when we returned closer to NJ we could see that it was overcooling.
Didn't notice any issues with MPG on the trip.
Out Of Control!!
Joined: Apr 2019
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
It's jammed in good and tough to extract...
Master Surya did go after his.
I recommend you take this opportunity of this job to swap your SERPENTINE kit (idlers, tensioner, belt).
it's and additional 20mn for 4 bolts : a real piece of cake to save your time.
Last edited by CaliBenzDriver; Apr 24, 2025 at 02:46 PM.
Thread Starter
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that short pipe... I did not deal with.
It's jammed in good and tough to extract...
Master Surya did go after his.
I recommend you take this opportunity of this job to swap your SERPENTINE kit (idlers, tensioner, belt).
it's and additional 20mn for 4 bolts : a real piece of cake to save your time.
It's jammed in good and tough to extract...
Master Surya did go after his.
I recommend you take this opportunity of this job to swap your SERPENTINE kit (idlers, tensioner, belt).
it's and additional 20mn for 4 bolts : a real piece of cake to save your time.
Yep, got the kit from FCPEuro!
Thread Starter
Junior Member
Joined: Feb 2025
Posts: 21
Likes: 3
that short pipe... I did not deal with.
It's jammed in good and tough to extract...
Master Surya did go after his.
I recommend you take this opportunity of this job to swap your SERPENTINE kit (idlers, tensioner, belt).
it's and additional 20mn for 4 bolts : a real piece of cake to save your time.
It's jammed in good and tough to extract...
Master Surya did go after his.
I recommend you take this opportunity of this job to swap your SERPENTINE kit (idlers, tensioner, belt).
it's and additional 20mn for 4 bolts : a real piece of cake to save your time.
Is a vacuum coolant fill required to refill the system? Or can I fill the system by having the car angled (front raised) and fill through the reservoir?
Out Of Control!!
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From: Silicon Valley
W212 MY'14 M276-3.5NA @75kMi
seriously easy
Simply as-is works perfectly fine: parked flat with no vacuum pumping, nothing.
As easy as you can imagine:
fill up
burp 5mn
top off perhaps half a cup morning after
Done!
Last edited by CaliBenzDriver; Apr 28, 2025 at 03:53 PM.
Thread Starter
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It's extremely basic. The urban legend of vacuum procedure is for shops that need to rush service.
Simply as-is works perfectly fine: parked flat with no vacuum pumping, nothing.
As easy as you can imagine:
fill up
burp 5mn
top off perhaps half a cup morning after
Done!
Simply as-is works perfectly fine: parked flat with no vacuum pumping, nothing.
As easy as you can imagine:
fill up
burp 5mn
top off perhaps half a cup morning after
Done!
Ok good. yea I didnt understand why everyone is so Gung-ho on it. I get it that it takes ALL the air out in one shot...but so does driving around a bit and allowing it to burp itself over time.
But like you said, its probably so Shops don't have to deal with post-work issues with the layman customer coming back when the coolant drops a little.
