Engine Coolant Temperature Sensor - W210 300 Turbo Diesel

[jamesf]

300 Turbo Diesel went into safemode yesterday - will not rev up.
Coolant gage sits at normal (80) and then skyrockets to 120+
Fans cut in etc. but car does not appear to be overheating - checked with thermal temperature sensor at thermostat housing.

Could a faulty Coolant Temperature Sensor be the fault?
i.e. Causing a false reading and sending the car into "safemode".

Also - assuming the sensor is under the intake - can sensor be changed without removing intake manifold.

[TMAllison]

A MB Laptop with SDS could prob tell you what is at fault.

Haven't flushed coolant or anything else coolant related recently? If so it may be low on coolant and need to be burped. Most 98's have a bolt on the head where the upper hose attaches. 99's don't.

What was the temp at the thermo when the dash registered 120C? What about at 80C?

There are two sensors. Haven't looked where they are located. Suspect the first may be part of the Overflow/Resivoir and the second in the head or possibly the block under the IM.

Coolant Level Sensor http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FU0VVLUG2GL0XYT9U&yearid=1999%40%401999&makeid=MB%40%40MB%40%40X&modelid=E%2D300DT%2D001%40%40E+300+D+Turbo&catid=G%40%40Cooling+System&mode=PA&subcatid=G1050@@Coolant+Level+Sensor&source=www.peachparts.com&clientid=catalog.mercedesshop

Water Temp Sensor http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FU0VVLUG2GL0Y3D9X&yearid=1999%40%401999&makeid=MB%40%40MB%40%40X&modelid=E%2D300DT%2D001%40%40E+300+D+Turbo&catid=P%40%40Body+Electrical&mode=PA&subcatid=P4036@@Water+Temperature+Sender&source=www.peachparts.com&clientid=catalog.mercedesshop

[jamesf]

Originally Posted by TMAllison

A MB Laptop with SDS could prob tell you what is at fault.

Haven't flushed coolant or anything else coolant related recently? If so it may be low on coolant and need to be burped. Most 98's have a bolt on the head where the upper hose attaches. 99's don't.

What was the temp at the thermo when the dash registered 120C? What about at 80C?

>>Did not check at 80C but at 120C temp was about 90 - about what the thermostat should open at.

There are two sensors. Haven't looked where they are located. Suspect the first may be part of the Overflow/Resivoir and the second in the head or possibly the block under the IM.

Coolant Level Sensor http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FU0VVLUG2GL0XYT9U&yearid=1999%40%401999&makeid=MB%40%40MB%40%40X&modelid=E%2D300DT%2D001%40%40E+300+D+Turbo&catid=G%40%40Cooling+System&mode=PA&subcatid=G1050@@Coolant+Level+Sensor&source=www.peachparts.com&clientid=catalog.mercedesshop

Water Temp Sensor http://catalog.peachparts.com/RenderScriptTemplate.epc?_cmd=epccat_VehicleAAA&cookieID=2FU0VVLUG2GL0Y3D9X&yearid=1999%40%401999&makeid=MB%40%40MB%40%40X&modelid=E%2D300DT%2D001%40%40E+300+D+Turbo&catid=P%40%40Body+Electrical&mode=PA&subcatid=P4036@@Water+Temperature+Sender&source=www.peachparts.com&clientid=catalog.mercedesshop

See comments inline - thanks for your reply Wondering if a Bad Temperature Sender could cause the fault I am experiencing. The way the temperature gauge reacts - jumps instantly to 120 and that the car is not overheating makes me suspect electronics ... i.e. a sensor.

[Matt L]

Isn't there some Motronic magic which dampens your gauge? If so, it will sit at 80 until the temperature gets much above that, then suddenly move.

How's your water pump?

[TMAllison]

Originally Posted by jamesf

See comments inline - thanks for your reply Wondering if a Bad Temperature Sender could cause the fault I am experiencing. The way the temperature gauge reacts - jumps instantly to 120 and that the car is not overheating makes me suspect electronics ... i.e. a sensor.

I guess to be certain it isn't overheating you ought to shoot the temp of upper and lower hoses. You should see hot water enter the rad and leave it cooler.

Should also see the thermo become fully open at 95c(?). The dash gauge will continue to register 95C until coolant temp surpasses 110C at which time it will jump up to that level and begin registering correctly.

Have you checked that the elect connection to the gauge is snug?

[jamesf]

Thanks everyone ... this is fixed now - Bad pump - unplugged sensor (a bit of a trick to get my hands under the intake etc. Gauge quit jumping etc. Temperature really was accurate at the sensor - although the temp at the rad hoses still was not that hot)... Mechanic that was helping could not believe that Mercedes would build an impeller out of plastic that blew apart. Says he has never seen a pump that would do that - usually bearing etc.
Thanks everyone - a bit of a goose chase here but .... did only spent less than $200.00 on a new thermostat and pump. A bit of chasing around and this group beats going to the dealer anyday!