35d worsening gas mileage - solved- thermostat/fan/EGR cooler - DIY with pics

[josiahg52]

-11 to -18C outside today and I was running a solid 82 to 83C at highway speeds. I am very glad I put dedicated snow tires on the X5 this winter. I experienced DEF freeze for the first time this morning; it was -18.5C when I started her up according to the ambient temperature sensor.

[TriX5]

Curious, how do you know the DEF was frozen?

I park indoor (garage is part of the house) so I haven't experienced that yet.

[josiahg52]

Originally Posted by TriX5

Curious, how do you know the DEF was frozen?

I park indoor (garage is part of the house) so I haven't experienced that yet.

The check engine light came on. I used BMWhat and read the DTC which was "Reductant pressure control, plausibility Code: 4952".

I assume because it was frozen, it could not supply the proper pressure. After about 30 minutes of driving, I reset it and it didn't come on again over the next three hours or so I was driving. That combined with the fact that it was well below the -11C freeze point of the DEF solution and that the X5 was sitting in -10.5C to -18C temperatures for over 15 hours. I suppose I can't know for sure.

[bawareca]

But how in the world this engine will loose 13C in 6 seconds and heat-up 13C in 20 seconds on idle? Are you sure you are looking at the coolant sensor data and not the radiator outlet temp?

[London Lad]

Originally Posted by bawareca

But how in the world this engine will loose 13C in 6 seconds and heat-up 13C in 20 seconds on idle? Are you sure you are looking at the coolant sensor data and not the radiator outlet temp?

I'm using THIS which only has one water temp gauge ?

[josiahg52]

Originally Posted by bawareca

But how in the world this engine will loose 13C in 6 seconds and heat-up 13C in 20 seconds on idle? Are you sure you are looking at the coolant sensor data and not the radiator outlet temp?

Almost looks like intake temperature or something.

Originally Posted by London Lad

I'm using THIS which only has one water temp gauge ?

I have two of these. Unfortunately it's not with me right now so I can't see how it works on the X5. Works good on my Tahoe and M5.

[scorpioy]

I'd like to report back after replacing the themostat. Now the temp is around 89-90 degree most of time.
Thanks to ZetaTre and rest of people helped.

[ZetaTre]

My Z4 has a map controlled thermostat. When you stomp on the gas the coolant temperature drops extremely quickly and when the pedal is released jumps back almost as quickly. We are talking 4/5 secs to shave almost 20 degrees celsius.

At cruising the thermostat is barely open to maintain operating temperature, particularly in a diesel that generates little heat and with the massive radiator that the X5 has. If it opens all the way, for example because the spring can't hold the increased coolant flow the temperature will tank. That's why I took that swag about the thermostat opening up...

[London Lad]

Originally Posted by ZetaTre

My Z4 has a map controlled thermostat. When you stomp on the gas the coolant temperature drops extremely quickly and when the pedal is released jumps back almost as quickly. We are talking 4/5 secs to shave almost 20 degrees celsius.

At cruising the thermostat is barely open to maintain operating temperature, particularly in a diesel that generates little heat and with the massive radiator that the X5 has. If it opens all the way, for example because the spring can't hold the increased coolant flow the temperature will tank. That's why I took that swag about the thermostat opening up...

I suspect you are correct. I will enable the hidden menu water temp read out (if I can find the info and understand it!) just in case my scan gauge is reading the wrong temp for some reason but I don't think it is.

[bawareca]

Originally Posted by ZetaTre

My Z4 has a map controlled thermostat. When you stomp on the gas the coolant temperature drops extremely quickly and when the pedal is released jumps back almost as quickly. We are talking 4/5 secs to shave almost 20 degrees celsius.

At cruising the thermostat is barely open to maintain operating temperature, particularly in a diesel that generates little heat and with the massive radiator that the X5 has. If it opens all the way, for example because the spring can't hold the increased coolant flow the temperature will tank. That's why I took that swag about the thermostat opening up...

All gasoline BMWs after 1999 or so have electronically controlled thermostat. But what you wrote doesnt add up. When you LEFT OFF the gas the temp is raising 20C From where the heat will come if the engine is not loaded? And even more so not loaded diesel in a cold weather.