C63 Coolant Temp Fluctuating

[ash-22]

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,

 

[Jason63]

I don't know about MB thermostats but I do know BMW thermostats (made by Behr I believe) can fail in a very short time frame if you are unlucky. Genuine BMW parts come with a warranty that includes the labour to replace them - even if you fit the part.

 

[steveq]

That sounds like the new thermostat is failing.
I believe that there is a 2 year warranty on genuine MB parts.
I'm not sure how to claim on that given that you fitted it yourself.

Note to self - keep receipts for all MB parts bought.

 

[EmilysDad]

....

Note to self - keep receipts for all MB parts bought.

True, but the dealer will have a record of the sale

 

[Steve@Avantgarde]

Spec engine running temperature according to WIS is 85-92'c.

In other words when the car is on the motorway with cool air rushing into the engine, its normal temp will be 85'c give or take a few degress to allow for ambient air temperature. When you are sat in traffic stationary and it uses its fans to cool the engine it will rise to 92'c. Anything above that will be classed as overheating.

I would say your stat performance is bang on normal.