heater is working fine, but that uses the small electric pump. the hose from the top of the engine to the thermostat is not even warm after 10min idle and 15 min drive but the heater again works fine... any ideas?

 

also I am mainly worried about over heating the engine without knowing it and blowing a head gasket. would the warning system prevent this?

I knew someone with a honda and his belt broke but since the temp sensor was in the rad and coolant wasnt being pumped he thought it was still being cooled but he blew the gasket.

 

After warming the car up, look for movement in the expansion tank - this will confirm you're getting flow - either just look at it form the side or open it up. If the system is building pressure, I would assume that would be a good indicator also. I just replaced my thermostat too and could squeeze the hose after idling for ~15 minnutes or so no problem (wasn't too hot). What does your engine temp read on the display? I didn't get mine all the way up to ~85C, only to ~65/70. I'm not sure exactly where the temp sensoris, but I would guess it's in the engine block somewhere, not the radiator.

Seems like a lot of us '03 guys are having this problem right now. I also discovered my tranny plug was leaking too - you might want to give that a looksy if you haven't had that done yet...

 

>just changed thermostat now temp is fluctuating

What is the coolant temperature fluctuation between?

Use the steering wheel controls to read your coolant temperature from the display (from mileage menu).

The hose at the top front of engine (between thermostat and radiator) may not be warm after a certain amount of time because the thermostat isn't open yet. The thermostat is supposed to open when coolant is at 87 degree Celsius. And its freezing outside up here in the Great White North,... so it may take longer.

Why exactly did you change out your old thermostat? Take your old thermostat and boil it in water,... to see what temperature the old thermostat opens at.

>After warming the car up, look for movement in the expansion tank - this will confirm you're getting flow - either just look at it form the side or open it up.

Make sure you turn off the interior heater,... otherwise that "small electric pump" will cause a lot of coolant movement in the expansion tank. Anyways likely difficult to tell since engine is in idle,.. and if you see movement like from particles in your coolant,.. you should be thinking coolant change.

Coolant Temperature Sensor for M271 engine is on right (passenger) side of engine near the front and top,... little black thing with wires at breathing pipes which are above the headers.

If you start playing with the interior heater,... the coolant temperature will start to fluctuate since the interior heater gets heat from the coolant system.



BTW,.. please don't compare Mercedes to Honda!!!

Mercedes have a lot more sensors and warning system,... very sensitive warning system that'll throw various Visit Workshop warnings and maybe trigger your Mercedes to go into limp mode.

Your car computer monitors the outside temperature and coolant temperature, if its not getting the proper coolant temperature reading within a certain amount of time driving it will throw a Coolant Visit Workshop warning. If the coolant temperature warning are way off or it's not getting any, it may go into limp mode and trigger the radiator cooling fan on high (like a turbine) thinking worst case scenario, engine is overheating so cool it off fast.

 

ok thanks for the info. it was going from 75 to 60 and back, i guess as the thermostat opened up it cooled the engine, then closed, then repeated until it levelled out. working well now and engine is finally getting hot again. I have the check engine light for engine not getting to proper heat or something.

 

did u acutally try driving it? to get it up to temperature?

your temperature should be between 90c and 80c....

take the coolant cap off the tank and let it run until its up to 87c

this is how u bleed out the air in the coolant

 

You shouldn't be going back and forth between 75 and 60,.... it should slowly get up to about 87 degree Celsius and stay there,... unless you're turning on and off the interior heater which gets heat from the coolant.

The thermostat should only open up at 87 degree Celsius. Yes, that temperature bar graph on our display sucks!

Also follow SammyDragon3's advice,.... in addition, very carefully squeeze some of the rubber radiator hoses,... do this very carefully as there are moving parts like pulley belts and radiator fan nearby. Squeezing will get the coolant and air bubble moving,... this is optional,.... or you could wait for the coolant system to do it itself over time,.... ideally put the cap back on and drive around a bit and top off the coolant in a day or so.

Which CEL light did you get? Better yet, which malfunction light did you get first. What exactly did it say on the display??? Usually when one malfunction light goes off,... a couple of others will get triggered as well. Did anything else happen beside the malfunction warning? Did the car go into limp mode? Did the radiator fan go full blast? Do you have a ODB2 scan tool? If not, get one.

 

I'll bet the system had air in it and required bleeding or patience. If it does not settle down make the supplier give you another new thermostat.