engine temp.

[RJ237]

I drove with the Ultragauge plugged into the OBD port for the first time today. Cruising at 2200-2400 RPM the temp. was 208 F, but when I climb a steep hill in the lower gears at 4000+ the temp drops to about 194, then slowly creeps back up when the revs drop at steady speed.

Is the water pump actually that inefficient? I'm thinking of changing the pump and thermostat but if this is normal operation I don't want to waste the time and money. At 105K mi I would think the pump has been changed at least once.

I have not found any posts where the operating temp. was monitored for a comparison, but maybe some of you have checked with a reader and can comment.

[gmushial]

I believe the thermostat is actually controlled by the engine management software, ie, it is commanded to open and closer by it... and it not like a mechanical bi-metal thermostat of years gone by. ... so: if the software wants to do what it's doing, changing either pump or 'stat isn't going to change anything.

[jclausen]

As interesting as this information is, it is in some ways to much info. I agree with the above comment. Since your Z4 has the m54 engine the thermostat and water pump change would be preventive maintance, I also believe there would be no change in the running temps

[RJ237]

This is a little hard to understand. Are you saying that the ECU opens and closes a motor driven thermostat? The pictures I have seen show what looks like a typical coil spring thermostat. I have a lot to learn and I don't find much in the way of information from BMW.

[RJ237]

I should have searched a little more before responding. Now I see that there is a heater in the thermostat controlled by the ECU that melts the wax.

[BimmerBreaker]

None of this is an issue. The engine is not overheating and the coolant is within operating temperature.

More RPM = more coolant flow = cooler

When its under load (4000 rpm uphill) it cools more because the engine is working harder. When it is cruising it is designed for the engine to reach the temperature which allows most efficient combustion.

[gmushial]

None of this is an issue. The engine is not overheating and the coolant is within operating temperature.

More RPM = more coolant flow = cooler

When its under load (4000 rpm uphill) it cools more because the engine is working harder. When it is cruising it is designed for the engine to reach the temperature which allows most efficient combustion.

Breaker offers a cogent comment: internal combustion engines are most efficient at higher temperatures... but it's a trade off between efficiency and being able to control the processes... the truly efficient hypermileage engines, actually run without "coolant", other than maybe the lube [some high temp chemistry material, but not oil as we know it]... basically heat shed to cooling, is thermodynamic inefficiency.

[BimmerBreaker]

Yes, exactly. A design goal of the cooling system is to maintain consistent combustion chamber temperatures. The car will lower the coolant temperature below "normal" operating temperature under high load because the internal engine temperatures are higher. When this happens the pump is running faster, more coolant is going through the radiator and cooling off, and this colder coolant will help maintain what should be the "normal" temperature inside the combustion chamber as it will absorb more heat from the hotter engine block. Under lower loads temperatures stabilize.

The BMW N52 normal oil operating temperature is 250F for this reason... efficiency.