Poor fuel consumption X5 diesel

[Clavurion]

Originally Posted by josiahg52

Celsius

So the final running temp is OK. Have you blocked the front (of the radiator) for winter?

How much back pressure on DPF?

[josiahg52]

Originally Posted by Clavurion

So the final running temp is OK. Have you blocked the front (of the radiator) for winter?

How much back pressure on DPF?

I do not and have never blocked the radiator.

I don't know about back pressure, but the differential pressure which varies with engine load is usually less than 0.1 psi at idle. I'll verify tomorrow morning.

[andrewwynn]

You should def block the radiator maybe 1/2 to 2/3 in winter.

The newer cars like my wife's have a shutter built into the grill and does it automatically


–awr–

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[Clavurion]

Originally Posted by andrewwynn

You should def block the radiator maybe 1/2 to 2/3 in winter.

During winter you should block nearly the whole radiator on top of the intercooler. A ~10 mm sleep padding can be easily installed between radiator and power steering cooler. No point driving cold air into engine bay when heat is scarce.

[andrewwynn]

I usually block 2/3 of my radiator from dec 1 (first day of winter) until mar 1 (first day of spring).

I have N55 motor. I live where we can have a random 70F day in the middle of winter so i don't block the whole thing.

As long as i turn my coolant pump to idle* the engine will get to 70-80C in 7-8 minutes of moderate driving.

On N55 motor, turn off cabin heat and the coolant pump will run about 45 rpm vs. 150 (70%! Reduction).

If i don't turn off the heater, i can't get cabin heat on 20 min. drive to work.

If i do i can get full heat in 7-8 minutes i just use seat and steering heat for the first 1:3 of the trip.


–awr–

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[josiahg52]

I don't see the need. Modern BMW diesels (like the M57) already manage coolant, oil, charge-air, and emissions temperatures as a system. Thermostat operation and coolant temperature are part of a larger overall cooling strategy involving fueling, EGR control, radiator airflow, fan control, and regeneration logic, rather than being governed solely by a fixed-temperature thermostat.

- I see a 10-15 °C coolant increase during regeneration on these coldest winter day, which tells me airflow and heat rejection are functioning as designed.

-I’ve seen oil temperature overshoot on another modern diesel when airflow was restricted - coolant looked fine, oil didn’t.

- Heater output is warming up within ~0.1 mile and fully comfortable by ~1 mile, and fully hot within 5 miles even on the coolest days, which indicates normal warm-up behavior.

Partial radiator blocking may (surely does) help older mechanical diesels, but on modern emissions-controlled engines it can upset oil, charge-air, EGT, and fan strategies without improving warm-up. If coolant temps are stable and regen behavior is normal, blocking airflow isn’t fixing a problem — it’s overriding the system.

In my case, the cooling system behavior matches design intent. Regenerations occur normally and raise coolant temperature into the ~90-94 °C range (exactly the same as in tge summer on the hottest days), cabin heat comes on very quickly even in extreme cold, fuel consumption is normal for conditions, and DPF soot/ash modeling remains stable with no regen issues. This behavior has been consistent for ~60k and the ~130k miles before that, with no under-temp faults. This indicates to me the overall cooling and thermal strategy is functioning as intended, even though steady-state cruise temps are lower in deep winter.

I do not and have never blocked my radiator. I'm not sure what function or performance it's supposed to improve in my case.

[josiahg52]

189,695 miles on my X5. It was -15C this morning. It had warmed up to -13.5C by the time I got to my destination.

At −15 °C ambient my M57 shows DPF ΔP ~0–0.02 psi at cold idle, ~0.04–0.06 psi at ~78 °C idle, ~0.40–0.45 psi at 45 mph (~80 °C), and ~0.68–0.75 psi at 60 mph. Converted that’s ~0–1.4 mbar idle cold, ~3–4 mbar idle warm, ~28–31 mbar at 45 mph, and ~47–52 mbar at 60 mph. The values scale with exhaust flow as expected and are within typical healthy ranges, and regens complete normally with coolant rising into the low-90s °C.

I see no reason to change anything I'm doing.

[andrewwynn]

"80c is a struggle" is exactly why I'd be putting a screen in front of part of the radiator. In fact i have to make a home Depot run in an hour and it's 2F out I'll be doing just that. Last run temp never got over 90 on a 40-50 min. round trip.

Whatever the heat profile is on a 15c day I would want to see similar.

I don't know what the thermostat opens at or if on the diesel it adjusts the coolant temp on the fly but when it's above freezing out my engine will run about 108 and drop to mid 90s under load.


–awr–

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[josiahg52]

Originally Posted by andrewwynn

"80c is a struggle" is exactly why I'd be putting a screen in front of part of the radiator. In fact i have to make a home Depot run in an hour and it's 2F out I'll be doing just that. Last run temp never got over 90 on a 40-50 min. round trip.

Whatever the heat profile is on a 15c day I would want to see similar.

I don't know what the thermostat opens at or if on the diesel it adjusts the coolant temp on the fly but when it's above freezing out my engine will run about 108 and drop to mid 90s under load.


–awr–

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80C is a "struggle" on a NEGATIVE 15C day. At 15C ambient, it runs 85C+.and reaches that within ten minutes of 35-45 mph driving. If "too much" cooling were an issue, it would never regenerate the DPF and never attain the 90C+ during regeneration. The M57, as are most diesels, is very efficient and just doesn't make a lot of heat. That's why there's an entire temperature strategy on modern DDE-controlled diesel engines that involves multiple systems. This ties in with the mandated emissions control requirements also.

[Clavurion]

Then again the very same powertrain for example on E6x with kidney active shutters they are closed 98% of the time. There is no point driving cold winter air in the engine bay and it even makes the aerodynamics slightly better to guide the air on the streamline.