Bhopkins

For those of you with the 2007-2009 SL550 with the M273 engine, what is the normal engine operating temperature that most of you observe on your coolant temperature gauge?

I've recently replaced the thermostat on my '07 SL550, and the temperature now stays at right about 92-93°C. When I first got the car, the temperature was running about 85-88°C. I'm curious if the new thermostat is running high, or if the old thermostat was already going bad when I bought the car. I've done a lot of online research and can't find anything that states what the correct thermostat temperature is supposed to be.

bellwilliam

what is the question? is it when does thermostat starts to open? even that is an approximation.
or is it what is a normal operating temperature for an engine? that would depend on outside temp.
manufacturers like to run high temp for emission and efficiency reason. but anything over 100c is considered hot... anything over 110c is a big no no...

btw, what temp thermostats open ultimately don't have to do with what coolant temp ends up to be in a long drive (in a warm weather). it mainly affects how fast it reaches that temp.

Rudeney

Mine usually runs around 90C. On a very cold day, it may stay closer to 80C, but on a hot day, it can climb to 100C and then the engine suction fan will kick on to cool it down.

Bhopkins

My question is what is the normal coolant operating temperature that others see once the car is fully warmed up.

My understanding of the function of a thermostat is somewhat different than yours. Yes, the thermostat does control how fast an engine gets to operating temperature. But my understanding is that, with modern cars it's function is also to assist in maintaining the engine at an ideal temperature for efficient operation. The thermostat helps maintain temperature by not only opening at the right temperature, but also by closing. This is particularly important in cooler weather. An ecu throws a code when engine temperature runs lower than normal because a cold running engine does not run efficiently. In most cases, replacing the thermostat fixes this.

Hendrik Koster

On my 2007 SL 55 P030, on the instrument cluster I can select a constant read out for the oil temperature it blinks an oil can symbol (simulating a warning) until it reaches 80 degrees C (after which it goes steady and shows the oil the actual oil temperature inside the engine) and according to the owners manual only than you should step on it.

I use this option almost 99% of the time and I have observed that my water temperature gauge will be in the normal range 80-95 (within 3-4 miles) way before the oil reaches the 80 degree C safe zone (which on average takes 6-10 miles of driving time)