What is engine temperature? My roadster, along with most other cars I've owned, has a water temperature gauge. After a few, usually less than 2 miles the dial shows 80 or 90 degrees. The fan cuts in now and then to keep the needle below 100.
But does this measure engine temperature or just water temperature?
My 2013 BMW has only an oil temperature gauge.This takes 5 to 10 miles to reach normal; long before the oil is warm the heater works well.
So, my conclusion: for the first 10 to 15 miles the water temperature gauge is fairly meaningless as it simply shows how hot the water is, nor how hot the engine is. Once the engine and oil have reached a steady temperature state the water gauge is probably enough. But how do you know the motor has reached steady state? Also without an oil temperature gauge it is not possible to know what is happening, and more importantly if an oil cooler is ever needed. Over-cooling oil isn't a good idea, like the rest of the engine it needs to be at a constant 80 to 90C.
So why does the industry (other than BMW) fit water temperature gauges?
Interestingly on the MOG it is possible to use the oil pressure gauge as a proxy oil temp gauge. Cold the oil pressure is about 5 bar. It stabilises at 1 bar at idle, 2 bar at 5000 rpm, but as with the BMW it takes 10 miles or so to get there, long after the water is hot.
