Hi all, what do members think of this.
Temperature gauge reads 90 to 92 degree Centigrade.
New temperature sending sensor.
Infra red temperature gun shows the following temperatures.
Upper radiator hose 65. Lower hose 46.
Cylinder head at base of injectors 70,85,74,72 and 67 degrees on 1,2,3,4and 5 cylinders.
65 degrees at external surface of sending sensor.
I can only conclude problem with gauge inside dash or electrical connection.
Any advice or further diagnosis would be appreciated.
Thanks

65 at the upper hose seems low. What is it at the thermostat housing? Is it the right sender? Quality brand?

Sixto
83 300SD
98 E320 wagon

Very Close to 80 C should be normal.
If the "Representation of a Temperature Gauge" system is operating properly

Remember, the Temp Gauge system is Almost as accurate as the "Oil Pressure Gauge System"

What's the reading @ the Thermo housing in "C"

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'84 300SD sold
124.128

OK so I tested the IR gun and it confirms that water boils at 100 degrees C.
The upper hose is now showing 80 and the thermostat housing 75. The expansion tank 45 degrees.
I had better check the thermostat. I recently replaced it but did not test it.
The sensor is probably Chinese crap but the temp gauge reads the same as before the sensor was changed.

If it's reading the same as before you changed the sender, I'd strongly suspect that you are indeed running hot. Keep in mind that the castings you measure won't be the same temperature as the water that's contained inside of them. They'll be quite a bit cooler. The IR gun also has a "window" or "area" that it measures, not just the laser dot, so the measured temperature is an average of the "area". They get significantly less accurate the further you are away from what you're measuring.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Heat problem on my 83 300sd was just solved by replacing the thermostat,Mono valve,and the climate control unit with a new old stock I found on E bay for $100.dollars. I sheared a bolt on the thermostat housing so I found another used one but the EGR sensor threads were 1 size bigger.A trip to Lowes pluming department had a reduction bushing in brass part # BF-738NLB-877199 for less than $2.00 solved that problem along with using 2 wraps of Teflon tape. Be aware of the 2 plastic vacuum ports not to break them like I did. Had to fabricate 2 tiny stainless tubes, gently tap them in place then used super glue to seal any vacuum leaks then again use Teflon tape to prevent any coolant seepage. while at Lowes I also bought two packs of stainless steel bolts to replace the steel bolts for the next time I have to replace the thermostat & gasket next year. I applied never seize grease to the three bolts that hold the two housing pieces together.For a safety precaution I installed a fuse holder using solder and shrink tubing to prevent the auxiliary water pump motor from damaging the new climate controller. That plug is located right next to the mono valve. Bye t5he way, the metric stainless steel screws are size M6-1.00X20 located in the hardware section of the store and come 5 in a package and cost a mere $1.89.I hope this solves any heater or temperature problem you may have. You can try one item at a time but I got tired of cold feet and punching the side of the climate controller consul to get the stupid heater fan to go on. When it started to blow cold when the outside temperature was in the 20's, that was the last draw that pushed me over the edge to "shot gun" the problem.