I have an issue I'm struggling to pin down with my 2010 318d 3 Series Touring: All air vents blow cold or at best, luke warm air into the passenger compartment, even on long journeys when the vehicle is at operating temperature. I've had the car diagnosed and done some digging myself and I'm completely stuck as to what the problem could be.
I've attempted to aggregate all the information I can about the car, potential issues and checks made for each one. I must be missing something. Any advice on how to proceed would be fantastic.
BMW 3 Series Touring E91 318d Production Date 08/2010.
150,000 miles on clock.
Engine code N47T.
Air vents blow cold, barely warm air, even when max heat is requested and vehicle is driven hard.**
- When set to 28 degrees, HVAC system blows luke warm air into car.
- OBD (ETC) coolant temp reads 85 degrees C during normal driving/idle.
- Car does not overheat/run cold (although milage is slightly lower than expected, MPG (UK) in high 40s, my old E46 320d ran in mid 50s)
- Coolant lines to and from heater core matrix are hot (almost too hot to touch) at operating temp.
Possible Causes & Investigation
1. Broken water pump/broken impeller?
- Removed aux belt, checked for play in water pump pulley, no play.
- Car running, removed expansion tank cap, coolant flowing into tank via small hose between expansion tank and top hose. ("fork to expansion tank 17127803838")
- Car doesn't overheat, no noise from water pump. Coolant appears to be following correctly.
- -> Water pump appears to be working correctly. Necessary to remove to inspect impeller?
2. Faulty Thermostat?
- Car runs up to 85 degrees C ETC according to OBD scanner. Holds operating temp at idle and during normal driving.
- Bottom radiator hose remains cold until engine is warm. Once warm, bottom hose heats up.
- -> Stat seems to be working correctly. Replace as preventative maintenance anyway?
3. Heater Matrix Blocked?
- Inlet and outlet pipes to heater core matrix get hot.
- Followed the guidance in the following pdf regarding flushing the heater core matrix with a hose: https://www.bimmerfest.com/forums/attachment.php?attachmentid=582821&d=1480064170
- Water flows both directions through the heater core easily. Small amount of sand came out during flushing
- -> Could be partially blocked still. Could have radweld or other blocking flow through majority of channels?
4. Coolant Low?
- Front of car jacked 60cm, engine run up to 85 degrees, coolant topped off and bled. Coolant level checked when car level and cold.
- -> Coolant level is fine.
5. Coolant system Airlock?
- See above, system bled thoroughly.
- -> Airlock unlikely.
6. Faulty HVAC Mixer Flaps/stepper motor/s?
- According to diagnosis by JMF Motor Worx, the stepper motors aren't showing any faults and have been re-addressed.
- Useful info here re. controller schematic: http://www.shrani.si/f/2z/Eu/2cbNKAhv/e90-climate-control.pdf
- -> Mixer flaps/stepper seem to be ok. Flap could be broken.
7. Faulty Auxiliary Water Pump?
- Specced on early e9x models, mostly petrol, doesn't seem to be specced on LCI diesels.
- ->Vehicle doesn't appear to have an auxiliary water pump.
8. Faulty Changeover valve /heater core matrix solenoid?
- Car not specced with Auxilary fuel heater: https://www.realoem.com/bmw/enUS/showparts?id=UT32-EUR-08-2010-E91N-BMW-318d&diagId=64_1785
- -> Vehicle doesn't have changeover value solenoid.
9. Faulty Electric Auxilary Heater
- Part name, quantity, (date), part number: Auxiliary heater 1 03/2010 64119194595
- According to JMF Motor Worx, the car is flagging a code for a faulty electric auxiliary heater.
- Vehicle appears to be specced with the heater (although some forum articles claim that UK vehicles aren't specced with them).
- -> Shouldn't affect heat when engine at operating temp, even if faulty. Fault might be causing other HVAC issues.
10. Faulty temperature sensor in HVAC system internals.
- See diagram here: https://www.realoem.com/bmw/enUS/showparts?id=UT32-EUR-08-2010-E91N-BMW-318d&diagId=64_1454
- 3 sensors total,
- Part name, quantity, (date), part number: Temperature sensor x2 64226915391 Temperature sensor, heater/evaporator x1 64116930015
- -> Possible?
11. Faulty Centre Console Climate Control Module
- -> Possible?
12. HVAC - Faulty temperature adjustment dial between middle dash vents. (Under DTC/lock buttons)
- Part name, quantity, (date), part number: Switch ZV/hazard warning flashers/DTC x1 03/2011 61319132421
- -> Dial could be faulty. Air is luke-warm from face vents, windscreen blower, foot vents, however. This dial controls temp of central vents only.
13. Faulty Recirculation sensor, under bonnet.
- Part name, quantity, (date), part number: Sensor f. AUC 1 64119240180
- -> Appears to control A/C and check quality of air for recirc/AC requirements. Unlikely to affect heat, but possible?
- Forum threads about similar issue with similar symptoms:
Any suggestions of how to proceed would be greatly appreciated.