No heat on the highway
 

I have a 04 X 4.4 with 107K on the clock. My wife complained last week that there was no heat in the X. Each time I went out to check it in the driveway it worked perfectly. I told her that she must have not been setting it correctly and began to become frustrated with her inability to learn. She has a tough time putting her sneakers on some days but that is a story for another time.

After driving it myself this weekend I discovered that I have no cabin heat when on the highway only. It works fine in the city and on back roads at slower speeds. It seems that when the HVAC thermostat is satisfied and the valve closes it will not reopen on the highway. If it is heating when I enter the highway it will heat until it satisfies and then no more heat till I get off the highway. Then it works as normal. I found that if while I am on the highway if I pop the transmission into neutral for a 5 seconds and the RPM's drop back to idle, the heat will immediately come back and the cycle will repeat.

In attempts to determine the root cause I have disconnected the water valve wiring and jumped back on the highway... This resulted in run away heat with dash vent temps of about 170 degrees no mater what you set the HVAC system for.

I have read the posts on HVAC issues but there is nothing quite like this issue that I could find. It is getting cold in New Hampshire. Any ideas on this besides the need to eat crow with the wife?

Thanks,

Eric

My guess the lack of replies is because no one has come across this. Seems very strange. In thinking through the process of how the heater core works, it almost seems illogical. I can't personally deduce what might be causing it. I hope you get it figured out soon.

I noticed the silence on this one... It has been driving me crazy. Like you said it just does not make any sense. I think that the system monitors moving speed and RPM's but i do not know why or what the system does with the information from the sensors. As soon as the engine drops back to idle, the valve opens and heat is restored. I also think that the drivers side of the system is somewhat cooler than the passenger side.

Sounds like you may need to bite the bullet and pay the $120 diagnostic at the dealership..

From reading on another thread, somewhat unrelated, investigate the 'heater resistor.' This controls the radiator fan and may play a part in this prob. Sorry I couldn't be more insightful.

This was a very well known problem on my E28-not sure if the X works the same or not but the problem is identical. The rubber diaphragms in the heater valve would develop rips. At highway speed the pressure in the cooling system would be high enough to force the coolant through the rips and back into the radiator--essentially bypassing the heater core. As soon as the engine speed was reduced the valves started working normally again. They used to sell just the rubber pieces but then stopped. Had to get a new valve at that point.

Good luck.

Edit to clarify that the valves and sensors always were working-just that the piece inside meant to divert coolant to the heater core failed.

The lack of replies is because topics like this have been discussed before. Look at the how-to articles above on how to bleed the cooling system properly and and a replacement thermostat. I'm guessing the spring portion itself on the thermostat is stuck open, causing too much flow and never letting it get warm enough while driving down the highway. Since you're not moving as fast when off the highway, the radiator is allowed to heat up again. If you're X has around 100k miles, I always suggest a complete cooling system overhaul.

Received a call from the Inde that is workin on the no highway heat in the X. He says after checking everything twice and not finding any error codes or other issues that he swapped out the water valve with another X that he had access to and found that it worked correctly. This was after a 7 series came in with exactly the same problem. Says been serviceing BMW's for 20 years and has not seen this symptom before.

He has ordered a replacement and promises a warm X on Friday. I am hopeful but not holding my breath. Will post final resolution when complete.

I have this same issue right now with my 4.6. was this the issue?

I had a stuck open thermostat in a car one winter which didn't have any heat on the highway but heat in city driving.