C63 Coolant Temp Fluctuating
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Joined: Mar 2021
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C63
C63 Coolant Temp Fluctuating
Hi Everyone!
Just wanted a bit of advice - owned my C63 W204 a few years now and ran into an illuminated EML a couple months ago. Code: 0856 "Coolant temperature is below thermostat specified temperature".
Changed Thermostat, radiator hose seal and flushed coolant. Test drove 400-500 miles no issues temperature needle steady & AMG cluster was showing 91-94C depending on driving conditions/weather (as was the case before the change).
Fast forward to few days ago - I'm finding the following:
Motorway 70mph+ = Coolant temp drops to around 82C (needle drops to 80 mark)
Standstill traffic or up to around 30mph = Coolant sits around the usual 93-94C
HVAC works perfect no heating issues
NO EML illuminated
Is this another failing thermostat? The Mercedes specialist SPR AUTO's in Stockport I purchased the Genuine Part from state this above is completely normal in the current UK weather but I haven't received the same information from a Mercedes Technician.
Look forward to any help/advice.
Thanks,
Just wanted a bit of advice - owned my C63 W204 a few years now and ran into an illuminated EML a couple months ago. Code: 0856 "Coolant temperature is below thermostat specified temperature".
Changed Thermostat, radiator hose seal and flushed coolant. Test drove 400-500 miles no issues temperature needle steady & AMG cluster was showing 91-94C depending on driving conditions/weather (as was the case before the change).
Fast forward to few days ago - I'm finding the following:
Motorway 70mph+ = Coolant temp drops to around 82C (needle drops to 80 mark)
Standstill traffic or up to around 30mph = Coolant sits around the usual 93-94C
HVAC works perfect no heating issues
NO EML illuminated
Is this another failing thermostat? The Mercedes specialist SPR AUTO's in Stockport I purchased the Genuine Part from state this above is completely normal in the current UK weather but I haven't received the same information from a Mercedes Technician.
Look forward to any help/advice.
Thanks,
MBWorld Fanatic!
Joined: Jun 2009
Posts: 1,372
Likes: 412
2010 C63 AMG
Totally normal, your thermostat may be stuck open which is getting you that much lower freeway temp. If that’s the case the car will take longer to get to operating temperature from startup and throw a code. I wouldn’t sweat it unless it throws a code and even then it’s not the worst or most immediate type of repair you would need to do as it’s simply overcooling the engine.
MBWorld Fanatic!
Joined: Mar 2010
Posts: 5,894
Likes: 324
From: CH = Land of mountains, cheese, chocolate and watches
12' W204 C63 AMG coupe "T-Rex", 12' W451 Smart Fortwo Pulse (99' W202 C43 AMG + Ultima Can-Am sold)
Don't think over cooling is a good procedure. Modern engines specially MB ones like to run hot and with proper pressure building in the system the water can get much hotter before doing any issues. Just my 2c though.
Is the cooling fan running when highway driving perhaps? This could give a cooler than normal temperature. Dodgy temperature sensor?
Is the cooling fan running when highway driving perhaps? This could give a cooler than normal temperature. Dodgy temperature sensor?
Junior Member
Joined: Apr 2019
Posts: 63
Likes: 9
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Hi Everyone!
Just wanted a bit of advice - owned my C63 W204 a few years now and ran into an illuminated EML a couple months ago. Code: 0856 "Coolant temperature is below thermostat specified temperature".
Changed Thermostat, radiator hose seal and flushed coolant. Test drove 400-500 miles no issues temperature needle steady & AMG cluster was showing 91-94C depending on driving conditions/weather (as was the case before the change).
Fast forward to few days ago - I'm finding the following:
Motorway 70mph+ = Coolant temp drops to around 82C (needle drops to 80 mark)
Standstill traffic or up to around 30mph = Coolant sits around the usual 93-94C
HVAC works perfect no heating issues
NO EML illuminated
Is this another failing thermostat? The Mercedes specialist SPR AUTO's in Stockport I purchased the Genuine Part from state this above is completely normal in the current UK weather but I haven't received the same information from a Mercedes Technician.
Look forward to any help/advice.
Thanks,
Just wanted a bit of advice - owned my C63 W204 a few years now and ran into an illuminated EML a couple months ago. Code: 0856 "Coolant temperature is below thermostat specified temperature".
Changed Thermostat, radiator hose seal and flushed coolant. Test drove 400-500 miles no issues temperature needle steady & AMG cluster was showing 91-94C depending on driving conditions/weather (as was the case before the change).
Fast forward to few days ago - I'm finding the following:
Motorway 70mph+ = Coolant temp drops to around 82C (needle drops to 80 mark)
Standstill traffic or up to around 30mph = Coolant sits around the usual 93-94C
HVAC works perfect no heating issues
NO EML illuminated
Is this another failing thermostat? The Mercedes specialist SPR AUTO's in Stockport I purchased the Genuine Part from state this above is completely normal in the current UK weather but I haven't received the same information from a Mercedes Technician.
Look forward to any help/advice.
Thanks,
