Is it possible to run too cool, if so, are there any ill effects to that and what is the ideal running temperature?

300D covers a few engines, best to tell year and model.

It is my understanding that 80C is best.

Running too cold will reduce your efficiency and power, can also lead to problems with the rings as well as moisture etc. in the oil that won't be able to evaporate.

__________________

Gone to the dark side

- Jeff

Jeff, thanks for the reply. The model in question is an 1985 300d. Thanks again.

The entire purpose of the thermostat is to maintain a specified minimum temperature. Thermostats are not installed for no reason.

The biggest issue with low temperature is wear. Fuel will condense on surfaces and wash away the oil film (less of a problem with diesels). Corrosive combustion byproducts will condense on surfaces. Corrosive byproducts and moisture will accumulate in the oil and not be driven off by temperature. Cold oil will not flow to the bearings as easily. Low temperature and lots of start-stop cycles will promote deposit formation in the ring pack and lead to stuck piston rings.

__________________
1987 W201 190D

Ideal temp is around 80-82C.....lower than 80C isn't good (though in the dead of winter is sometimes unavoidable....)

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I'm surprised at how well my temps lock on to 80c. Sometimes slightly cooler in the bitter cold, and only slightly higher during summer/traffic/ac use. Other than that it doesn't move. PO must have taken good care of the cooling system!

__________________