Erratic Temperature Gauge
Thread Starter
Junior Member
Joined: Feb 2020
Posts: 50
Likes: 6
C63 AMG
Erratic Temperature Gauge
Hey there,
Long time lurker here. I tried to search this topic and couldn't find any real definitive potential causes but here's my story:
I recently purchased a 2012 C250 Sport. After about a month, I got a CEL for the thermostat, so I purchased a Borg Warner/Wahler thermostat with the correct MB coolant. After my mechanic installed it, the temperature gauge has been erratic. For example, it'll go up to 80 within a minute or two of starting up and then driving, and if I turn the heat on, it'll go back down to 40, and then slowly creep up to 80, which seems like normal behavior; if I turn the heat on immediately upon starting, it'll quickly go up to 40 and then about 80; at one point, the temperature shot up to around 120 from 80, back down to 60, up to 90ish, and then back down to 80. Once the car actually gets up to a normal operating temperature, it seems to be fine and does not become erratic other than it going up and down from 80 to around 85 here and there.
Does anyone know what could be causing this? Faulty thermostat unit or temperature sensor; air bubbles in system (mechanic insists he vacuum filled it); coolant not mixed 50/50 with distilled water; too much/too little coolant; heater control valve (heat works fine...)?
Any help is appreciated. I haven't had the opportunity to check the coolant level while cold or bring it back to my mechanic since he's been on vacation.
Long time lurker here. I tried to search this topic and couldn't find any real definitive potential causes but here's my story:
I recently purchased a 2012 C250 Sport. After about a month, I got a CEL for the thermostat, so I purchased a Borg Warner/Wahler thermostat with the correct MB coolant. After my mechanic installed it, the temperature gauge has been erratic. For example, it'll go up to 80 within a minute or two of starting up and then driving, and if I turn the heat on, it'll go back down to 40, and then slowly creep up to 80, which seems like normal behavior; if I turn the heat on immediately upon starting, it'll quickly go up to 40 and then about 80; at one point, the temperature shot up to around 120 from 80, back down to 60, up to 90ish, and then back down to 80. Once the car actually gets up to a normal operating temperature, it seems to be fine and does not become erratic other than it going up and down from 80 to around 85 here and there.
Does anyone know what could be causing this? Faulty thermostat unit or temperature sensor; air bubbles in system (mechanic insists he vacuum filled it); coolant not mixed 50/50 with distilled water; too much/too little coolant; heater control valve (heat works fine...)?
Any help is appreciated. I haven't had the opportunity to check the coolant level while cold or bring it back to my mechanic since he's been on vacation.
Thread Starter
Junior Member
Joined: Feb 2020
Posts: 50
Likes: 6
C63 AMG
