Temperature issue (bit fresh)

[grounch]

Hi


Winter is here (well, kind of winter, it barely goes under 5°C here) and so are temperature related issues.


Driving normally in the city makes the temp reach around 70/80 when not heavy foot, but goes to the needed 90 when i give some load.
Same with uphills, heats fast when under load.


But the issue comes when i drive for example a few miles road downhill, so mostly let myself roll down without any engine load.
That makes the temp drop to around 75/80 and not goes back up until i rev it again.
The thermostat is supposed to open at 88°C.



Of course i thought it was the thermostat. Changed it (was a Denso, now a Hella, both good brands) but did not solved a thing..


Overally the car behaves fine, heat comes quickly to the vents, drives and idle ok, not really overconsuming.
It's a 2005 3.0d.
Lower coolant hose (from thermostat/pump to the rad) is warm but not as hot as the upper one.
Fan is not going crazy.
Temp gauge is in the middle and sitting there, but i've read it's not perfectly calibated, so i'm reading the temp value from the odb secret menu.

How is it behaving with you guys in winter?

Maybe i'm too obsessed having it working perfectly and 10° doesn't change much after all...
Because i have no idea what could be the issue after changing 2 thermostats.

[wpoll]

Check the viscous fan hub isn't "frozen" and spinning the fan at full speed at all times. These viscous couplers have a number of different failure modes... mine had a bearing failure but they sometime don't spin or sometime always spin. The coupling should be temp dependent and not spin (much) when the engine is cold.

[grounch]

Originally Posted by wpoll

Check the viscous fan hub isn't "frozen" and spinning the fan at full speed at all times. These viscous couplers have a number of different failure modes... mine had a bearing failure but they sometime don't spin or sometime always spin. The coupling should be temp dependent and not spin (much) when the engine is cold.

Tried that also, stopped the fan manually when cold and it did not have much resistance.

I know about this visco issue but it usually makes the car sound like a jet, which is not my case.

[Clavurion]

I've removed the viscous fan and left it on the shelf for several years without problems. For main stat only original BMW part is recommended. Most of those after market stats are the same Made in Italy lottery quality.

Does your vehicle have EGR cooler and EGR thermostat?

[ahlem]

How accurate is your temperature reading?

[grounch]

Originally Posted by Clavurion

I've removed the viscous fan and left it on the shelf for several years without problems. For main stat only original BMW part is recommended. Most of those after market stats are the same Made in Italy lottery quality.

Does your vehicle have EGR cooler and EGR thermostat?

The BMW OEM stat was around 2x more expensive than the others (around 90e), so i did not went for it.
No EGR cooler just the pipe from the manifold to the EGR valve (which is disabled, vacuum hose removed and hole plugged)

The reading is as accurate as what the ODB menu give, probably same as the value you get via the OBD plug.

[Bdc101]

If you are driving downhill with the car in gear for long periods, you can actually remove all the heat from your engine using the heater. You aren't adding any heat to the engine with fuel, but you are subtracting it by heating the cabin. In certain conditions this can indeed cause the engine temperature to drop down significantly. However a third-party thermostat could certainly be causing it as well.



Do you have a foxwell or other device that can show you the temperature sensors? My foxwell will show engine coolant and the radiator outlet temperature in real time. When the thermostat is shut, the radiator outlet temp should drop to around the same temperature as the atmosphere, but when the thermostat is open it will be closer to the engine coolant temperature. You might be able to diagnose a stuck-open thermostat in this manner.

[grounch]

Originally Posted by Bdc101

If you are driving downhill with the car in gear for long periods, you can actually remove all the heat from your engine using the heater. You aren't adding any heat to the engine with fuel, but you are subtracting it by heating the cabin. In certain conditions this can indeed cause the engine temperature to drop down significantly. However a third-party thermostat could certainly be causing it as well.

Do you have a foxwell or other device that can show you the temperature sensors? My foxwell will show engine coolant and the radiator outlet temperature in real time. When the thermostat is shut, the radiator outlet temp should drop to around the same temperature as the atmosphere, but when the thermostat is open it will be closer to the engine coolant temperature. You might be able to diagnose a stuck-open thermostat in this manner.

Have a laptop with INPA / ISTA, will see if i can have those 2 readings separately. It's a good way to diagnose the stat situation indeed.


Will also try to drive in same conditions without the heater on, if the temp doesn't drop that much this time it will confirm your theory. I don't put lot of heat (usually 21° and 2 or 3 bars of fan) but it still can take some heat.

[Clavurion]

Originally Posted by Bdc101

If you are driving downhill with the car in gear for long periods, you can actually remove all the heat from your engine using the heater. You aren't adding any heat to the engine with fuel, but you are subtracting it by heating the cabin. In certain conditions this can indeed cause the engine temperature to drop down significantly. However a third-party thermostat could certainly be causing it as well.

Do you have a foxwell or other device that can show you the temperature sensors? My foxwell will show engine coolant and the radiator outlet temperature in real time. When the thermostat is shut, the radiator outlet temp should drop to around the same temperature as the atmosphere, but when the thermostat is open it will be closer to the engine coolant temperature. You might be able to diagnose a stuck-open thermostat in this manner.

E53 has quite a lot of interior volume and lot of surface area dissipating heat so the heater core does take quite a lot of power (coolant temp) to keep the interior warm. With diesel engines the Webasto aids upto 75 C (same temp when temp gauge is 12 o'clock), but 75-90 C is is very suspect to engine load on cold weather.

Cluster hidden menu shows exactly the same temp you would get with diagnostics. These diesel engines don't have radiator outlet temp sensor.

[Bdc101]

Originally Posted by Clavurion

These diesel engines don't have radiator outlet temp sensor.

Ah, then in that case disregard my suggestion!