zygsterz1

Recently my 2005 SL500 intermittently starts bouncing around on the temperature gauge. The temperature sensor has been replaced. The coolant reservoir is full. It will start climbing in temperature and the red light comes on and off with a coolant message. It can bounce from 110 degrees to 84 instantly. Any ideas?

Plutoe

Sounds like you have a faulty thermostat-----get it changed!!

MJ50

moved to R230 forum...

cyglee

Is the temperature change related to whether the car is cruising with air flow through radiator, or stop and go traffic?

next2pool

If it bounces around that quickly, I suspect it is electrical and not the thermostat. The engine has a lot of thermal inertia and can't change temperature that quickly.

bobterry99

I don't believe this can be caused by the thermostat or any other component of the cooling system, as the temperature at the sensor is unlikely to be capable of such a rapid change. Instead, I believe it is an electrical issue with the wiring, a faulty engine management (ME) controller, or a faulty instrument cluster.

The sensor is wired to the ME controller, and the ME controller reports the temperature derived from the sensor on the engine CAN network.

I would suspect the instrument cluster is the problem and would check that first. For that I would use Star Diagnosis to read the temperature reported on the CAN. If the cluster is the problem, then at some point its display will disagree with what Star Diagnosis is reading.