Originally Posted by Dave_3
I've seen quite a few posts about coolant temperatures on the 335D - mostly in regards to EGR and main thermostats. Some as high as 90+.
What is the factory defined operating temperature for the coolant ? Does anyone know what the defined range is, rather than observed values ? And is it the same for pre and post ED variants ?
The main thermostat is rated at an opening temperature of 88C, hence the 88 - 92C working range we see in typical use. The same thermostat, as used in the Rover BMW M47R 2.0d engine is rated at 88C +/- 5C tolerance. BMW don't seem to declare that data for the BMW models.
EGR thermostat has twin stage elements, first stage 70C opening temperature, with restricted flow, and full flow (second stage) at 90C, to follow the main thermostat opening temperature. Otherwise (as another post states) the faulty EGR thermostat flow by-passes the main thermostat control and chills the engine, and/or prevents efficient warm up and optimum ECT.
If an EGR thermostat opens pre main thermostat (88C), assuming the main thermostat is still in tolerance, the engine will not reach peak ECT in normal use. Although it may still exceed 90C during a regeneration, as there is typically much more heat in the engine.