Mercedes A-Class Forum banner
Cancel
Create thread New Garage Forums

Fluctuating coolant temperature gauge?

Jump to Latest
76K views 118 replies 30 participants last post by  Jaycw177  
#1 ·
Hi, picked up a A200 auto a few days ago. Nice car but I’ve noticed the temp gauge goes up and down a bit between 75 and 90 even once car is warmed up. If your sat in traffic for instance it’ll sit around 90, as soon as you drive off somewhere it’ll drop down again! Shouldn’t it stay at steady 90 once it’s warmed up? Every other car I’ve ever owned has not done this. Surely it can’t be thermostat as cars only done 6,700 miles?
Thanks
 
S
#6 ·
It sounds like a working temperature control system to me. People have got used to cars showing a fake constant 90, as my VAG vehicle frustratingly does. The gauges are now coded so that one the actual temp reaches ~70 to 110 the gauge will display 90, outside of this the gauge will display the actual recorded temp.

They dumbed the display down because they determined people didn't need to see actual outputs - thus I couldn't see the warning signs that my water pump was failing. I miss old cars and their no nonsense outputs.
 
S
#8 ·
Well, that assumes that Merc have programmed this car to be a dumb gauge. What you describe is a gauge reading actual temps.

With regards other car's you've owned, VAG made this change in the mid 90s. Stuff before that actually told you what was really going on. If you've only owned more recent vehicles then there's a chance you've never read a gauge that's showing actual temps
 
#14 ·
I disagree with the poster regarding fluctuating temps being the norm. The water temp should get to around 90c and remain there. Any variation to this is indicative of a fault. I know through experience of this happening on several of my past cars. On some it was the thermostat failing and on one car it was the coolant temperature sensor.
 
#21 ·
Update.
Possible thermostat issue but Mercedes want it for a few days to test.
Only trouble is the next available courtesy car isn’t for about a month!
The guy said the needle shouldn’t really fluctuate once up to temp.
Cheers for all the replies.
Will update further when hopefully they fit a new stat!
 
S
#24 ·
Drove it at the weekend, must admit I was hung over and forgot to look most of the journey! But after some relatively relaxed A / B roads leading to the M40 the gauge was in the 3rd of the 4 sectors. After being sat on the M40 for 10 minutes at a 'rock and roll' 65mph the gauge went to dead centre and remained there.
 
S
#26 ·
It's the 200d, it will make a difference, TDI engines run quite a bit cooler than in-direct and petrol. Plus the bigger lump will have a more stable temp i.e. less fluctuation.

Yours still sounds almost normal to me. a fluctuation of 15. So sat in traffic it gets a bit warmer, perhaps the stat has opened but with no airflow it's not made much of an impact. Then you start driving again and the airflow quickly drops the temp and thus the stat closes and your temp rising back to 90 again.
Perhaps the stat is opening a little early, but I'd be surprised.

I'm very interested to hear the outcome - if they do change the stat I'd ask for the old one back so you can stick it in a pan at home and see what it's doing
 
#27 ·
sirweste said:
It's the 200d, it will make a difference, TDI engines run quite a bit cooler than in-direct and petrol. Plus the bigger lump will have a more stable temp i.e. less fluctuation.

Yours still sounds almost normal to me. a fluctuation of 15. So sat in traffic it gets a bit warmer, perhaps the stat has opened but with no airflow it's not made much of an impact. Then you start driving again and the airflow quickly drops the temp and thus the stat closes and your temp rising back to 90 again.
Perhaps the stat is opening a little early, but I'd be surprised.

I'm very interested to hear the outcome - if they do change the stat I'd ask for the old one back so you can stick it in a pan at home and see what it's doing
Click to expand...
Will update when it goes back into Merc (end March now though unfortunately).
I understand what your saying but it still doesn’t seem right to me, all journeys now once warmed up you can watch the gauge going up and down like a yo-yo between 70 & 90. No good for my OCD lol.
 
#31 ·
So i went yesterday to the service! They plugged the car to the ECU, they checked the thermostat of the car and it was ok! They did upgrades to MBUX, and machine! After the first ride, i noticed the temperature not changing to much! And i didn't have the big changes from 92 to 72 degrees, some 4-5 degrees changes.

I told them why Mercedes not calling us for ECU upgrades, and they told me that the car is going to take the upgrades only if something is wrong in the car.

So i had a problem, an ECU upgraded was already out, and i didn't knew the existence of it!

Congratulations to Mercedes
 
#32 ·
cboursinos46 said:
So i went yesterday to the service! They plugged the car to the ECU, they checked the thermostat of the car and it was ok! They did upgrades to MBUX, and machine! After the first ride, i noticed the temperature not changing to much! And i didn't have the big changes from 92 to 72 degrees, some 4-5 degrees changes.

I told them why Mercedes not calling us for ECU upgrades, and they told me that the car is going to take the upgrades only if something is wrong in the car.

So i had a problem, an ECU upgraded was already out, and i didn't knew the existence of it!

Congratulations to Mercedes
Click to expand...
hmm, interesting. Mines actually going in for software updates as well next week before they check the thermostat so I’m hoping it could just be that now! will keep my fingers crossed.
Thanks for the letting me know ??
 
#34 ·
cboursinos46 said:
I am going to raise an issue to Mercedes, i hope others will come with me, in order to receive notifications when new upgrades for ECUs are rolling out! Why to have a problem and and ECU update that i didn't knew the existence fixed my car!

This is bad customer support!
Click to expand...
I totally agree. Mine only recently went for a main dealer service so you would think the updates would of been done then!
You would think in this day and age there would be a system in place to keep customers informed so they have the choice wether to update or not.
 
#41 ·
I've read of a few update issues across several forums now.
Hardly surprising the dealers don't want to get too involved in firmware updates when it sometimes breaks the car.
Moving to Linux as definitely caused them some headaches in MBUX too.
No doubt a lot of retraining being required across the techs and developers.
 
Mercedes A-Class Forum
posts
208K
members
29K
Since
2012
We're a forum community dedicated to the Mercedes-Benz A Class . Come join the discussion on performance upgrades, accessories, troubleshooting, maintenance and more!
Full Forum Listing
Explore Our Forums
W176 A45 W177 General W176 General Newbies W177 A45 & A45s