MX Rear Heat Performance

[Jeff Songster]

Sure glad the Subzero pack is included in Premium... We got spoiled by having four heated seats and steering wheel in our Nissan LEAF SL. Heating the seats is far more efficient than using traction battery to heat cabin. Saves range.

 

[Yinn]

Turning the rear fan up will not make it blow hotter air. Quite the contrary, as the increased airflow will overwhelm its small heating element. I'd recommend setting the rear temp to HI (I don't trust its sensor) and the fan speed to 3 or 4 for best results.

I concur. I leave my rears on at all times since the seat sensors don't pick up my kids in car seats. Set to 3 with temperature sync for floor and vent and it seems to heat up just fine and in about the same time as the fronts.

 

[jbwinton]

UPDATE: I finally had my service appointment and their conclusion was that nothing is wrong with my rear heater.
They recommended starting off rear heat on "Hi" then backing off the temp as the cabin heats. They told me that it was normal when both front and rear were set the same (72 deg, fan 3 for example) that the front air feels hot, but the rear feels cool.
When using Hi temp setting for the rear, after a minute or so, I could feel warm air-- at about the same temp as the front with 68 deg set.
A quick check of running the rear heater in Hi, with fan=3, and outside temp 55, showed an initial consumption of 2430 watts, gradually ramping down over 7 minutes to 1215 watts and stabilizing. At the lower level, on a long trip, I would lose 3.8 miles of rated range every hour.
My conclusion: try to use just seat warmers and front heater if possible. If that isn't enough, the rear heater consumption is not a show stopper unless I am cutting it close on range remaining at destination.

this is another unacceptable design flaw in the MX. the manual and Tesla service say "rear heater doesn't work if no passenger in back seat" but that is wrong. if the rear heat is set to manual, it should produce hot air from the vents on the rear door pillar.

Mine did not and I had it in for service. they "fixed" some control that their computer told them wasn't working and for a few weeks I got hot air IF SET TO HIGH. now it only blows cold air again.

is there a fix?

does anyone know how long it should take for the rear heater (if working at all) to blow warm air. I would assume the heat comes from the same battery as the front heat, so it should be rather instant.

 

[ditzpro]

Rear heat sucks ..Really ridiculous for this car ...I live in Michigan and below 30 degrees , my friends in the back 2nd row (never use the 3rd) always complain ...I'm going to investigate changing the vents somehow ..Everything can be fixed , it just takes a little engineering and thought ..

 

[Big Earl]

Rear heat sucks ..Really ridiculous for this car ...I live in Michigan and below 30 degrees , my friends in the back 2nd row (never use the 3rd) always complain ...I'm going to investigate changing the vents somehow ..Everything can be fixed , it just takes a little engineering and thought ..

I don't think changing/modifying the vents is going to improve rear heat performance. The main issue is that the rear heating element is about 1/3 the size of the front heating element, so it can only provide so much heat. Setting the fan speed too high will overwhelm the rear heating element, causing luke warm air to come from the vents. It's also been noted that the heater performs better when you set it to HI instead of letting it auto-adjust the temperature.

 

[polymathic]

In my case, the driver's side rear vent blows cold air while the passenger side blows warm air. It's being investigated now at the SC.

Frankly, had I known the rear heaters would be so finicky, I would have gotten the winter package. Kind of bummed about this little glitch.

 

[Big Earl]

2

In my case, the driver's side rear vent blows cold air while the passenger side blows warm air. It's being investigated now at the SC.

Frankly, had I known the rear heaters would be so finicky, I would have gotten the winter package. Kind of bummed about this little glitch.

I'm a little confused by your wording. Do you have the rear HVAC system or are you talking about the two vents in the center console?

 

[polymathic]

2


I'm a little confused by your wording. Do you have the rear HVAC system or are you talking about the two vents in the center console?

I'm talking about the driver's side rear vent off the pillars. The tech was puzzled about how that was even possible.

 

[_jmk]

Umm, the 12V sockets should give 150W each. Maybe with some proper heater these could help.

 

[Big Earl]

Umm, the 12V sockets should give 150W each. Maybe with some proper heater these could help.

A 150 watt heater isn’t going to make a noticeable difference when total heating system performance is over 8,000 watts. A 12 volt electric blanket, on the other hand...

 

[_jmk]

A 150 watt heater isn’t going to make a noticeable difference when total heating system performance is over 8,000 watts. A 12 volt electric blanket, on the other hand...

Yeah, but on the other hand it is 2*180W max, so better than nothing as these things could be put exactly where needed. Your average sedan usually warms up just fine when attached to a heater pole and 700W heater blasting inside.

 

[Big Earl]

Yeah, but on the other hand it is 2*180W max, so better than nothing as these things could be put exactly where needed. Your average sedan usually warms up just fine when attached to a heater pole and 700W heater blasting inside.

While stationary/parked or while driving down the highway? It takes a lot more energy to provide comfort heating in a moving vehicle for a number of factors, including air leaks through seals and the required fresh air ventilation to prevent humidity buildup.

I've found that the Model X needs a fan speed of at least 5 or 6 (on the from HVAC system) to provide enough positive pressure to overcome any air leaks through the door and window seals. Bioweapon defense mode does a very good job and uses fan speed 8. If you're using a lower fan speed, you'll notice air leaks through the falcon wing doors. I think this is a major contributor to rear passenger discomfort in the winter. I've found the Model S to be similar with regard to fan speed and air leaks through the door and window seals.

Unfortunately, using a higher fan speed in the front means higher energy consumption because the system has to heat a higher volume of cold outside air. I'd need to play around some more, but my initial feeling is that a fan speed of 7 in the front and 4 in the rear is ideal for very cold weather at freeway speeds.

 

[_jmk]

While stationary/parked or while driving down the highway? It takes a lot more energy to provide comfort heating in a moving vehicle for a number of factors, including air leaks through seals and the required fresh air ventilation to prevent humidity buildup.

Stationary. Sure, I wasn't trying to propose the 350W would do anything alone when moving, but it might help. Maybe. That big heater can be running a really long loop with unknown insulation and this 350W could be directed exactly where the heat is needed.

I'll be getting my car finally tomorrow and it was -28C this morning here in Finland. I guess I will soon learn how good/bad it really is. One thing I don't entirely understand here is that Björn Nyland (the youtube hero) once arranged a sauna in he's model X. How did that happen if the heater runs out of power .... ?

 

[Big Earl]

Stationary. Sure, I wasn't trying to propose the 350W would do anything alone when moving, but it might help. Maybe. That big heater can be running a really long loop with unknown insulation and this 350W could be directed exactly where the heat is needed.

I'll be getting my car finally tomorrow and it was -28C this morning here in Finland. I guess I will soon learn how good/bad it really is. One thing I don't entirely understand here is that Björn Nyland (the youtube hero) once arranged a sauna in he's model X. How did that happen if the heater runs out of power .... ?

Bjorn was stationary, for starters. The heater also doesn't really run out of power. I think a number of complaints come from the automatic mode in the rear using too much fan, causing a wind chill effect that makes passengers feel cold. Keeping the rear fan speed down to a reasonable level can help a lot with passenger comfort. The front heater seems to be fine for most people.

Congrats on the new car! I hope you took tomorrow off of work so that you can get to know it.

 

[_jmk]

Congrats on the new car! I hope you took tomorrow off of work so that you can get to know it.

Thanks! I did take a day off, should be fun. I guess men never really grow up, toys just get bigger and more expensive..

 

[_jmk]

Several days of driving behind now at seriously severe weather (-25 - -30C). No heat issues whatsoever, car is very warm and very fast.

 

[jbwinton]

I have to get rid of my MX due to rear heat issue that tesla says CANNOT be fixed or improved. In Chicago when it's below 20F, it takes 50 minutes for the rear pillar vents to blow warm air. this is unacceptable in a $100k car !! People in back tell me they're cold.

I've had the car in service many times and they explain that the rear heater is very small . when DRIVING in cold weather it is just no good. Service tells me that PARKED it heats up faster but I can't get very far with the car in park so this is an irrelevant test. preheating doesn't solve the issue.

and to make things worse, when it's cold and I run both heaters on high it uses up about 25 miles per hour from the battery so that greatly reduces range. it get no where near the 235 mile range (75 battery). Do the math. charge to only 90%....use 50 miles for 2 hrs. to/from work....be sure not to get below 10% charge...that gives me a range of maybe 130-140 miles.

it's a really nice car if anybody wants to buy one that is perfect for warm weather climates like Florida or Calif.

 

[jbwinton]

While stationary/parked or while driving down the highway? It takes a lot more energy to provide comfort heating in a moving vehicle for a number of factors, including air leaks through seals and the required fresh air ventilation to prevent humidity buildup.

I've found that the Model X needs a fan speed of at least 5 or 6 (on the from HVAC system) to provide enough positive pressure to overcome any air leaks through the door and window seals. Bioweapon defense mode does a very good job and uses fan speed 8. If you're using a lower fan speed, you'll notice air leaks through the falcon wing doors. I think this is a major contributor to rear passenger discomfort in the winter. I've found the Model S to be similar with regard to fan speed and air leaks through the door and window seals.

Unfortunately, using a higher fan speed in the front means higher energy consumption because the system has to heat a higher volume of cold outside air. I'd need to play around some more, but my initial feeling is that a fan speed of 7 in the front and 4 in the rear is ideal for very cold weather at freeway speeds.

see my post today about TOTALLY UNACCEPTABLE HEAT issue in MX and let me know if your dealer has any better answers than mine.

I have to get rid of my MX due to rear heat issue that tesla says CANNOT be fixed or improved. In Chicago when it's below 20F, it takes 50 minutes for the rear pillar vents to blow warm air. this is unacceptable in a $100k car !! People in back tell me they're cold.

I've had the car in service many times and they explain that the rear heater is very small . when DRIVING in cold weather it is just no good. Service tells me that PARKED it heats up faster but I can't get very far with the car in park so this is an irrelevant test. preheating doesn't solve the issue.

and to make things worse, when it's cold and I run both heaters on high it uses up about 25 miles per hour from the battery so that greatly reduces range. it get no where near the 235 mile range (75 battery). Do the math. charge to only 90%....use 50 miles for 2 hrs. to/from work....be sure not to get below 10% charge...that gives me a range of maybe 130-140 miles.

it's a really nice car if anybody wants to buy one that is perfect for warm weather climates like Florida or Calif.

 

[jbwinton]

Rear heat sucks ..Really ridiculous for this car ...I live in Michigan and below 30 degrees , my friends in the back 2nd row (never use the 3rd) always complain ...I'm going to investigate changing the vents somehow ..Everything can be fixed , it just takes a little engineering and thought ..

see my post today about ABSURDLY POOR rear heater and pls let me know if your dealer has any better answer than mine.

I have to get rid of my MX due to rear heat issue that tesla says CANNOT be fixed or improved. In Chicago when it's below 20F, it takes 50 minutes for the rear pillar vents to blow warm air. this is unacceptable in a $100k car !! People in back tell me they're cold.

I've had the car in service many times and they explain that the rear heater is very small . when DRIVING in cold weather it is just no good. Service tells me that PARKED it heats up faster but I can't get very far with the car in park so this is an irrelevant test. preheating doesn't solve the issue.

and to make things worse, when it's cold and I run both heaters on high it uses up about 25 miles per hour from the battery so that greatly reduces range. it get no where near the 235 mile range (75 battery). Do the math. charge to only 90%....use 50 miles for 2 hrs. to/from work....be sure not to get below 10% charge...that gives me a range of maybe 130-140 miles.

it's a really nice car if anybody wants to buy one that is perfect for warm weather climates like Florida or Calif.

 

[Big Earl]

I hate to say it, but welcome to an X 75 in the winter. You will get nowhere near the rated range in cold weather. The same goes for the 100, but that at least has more energy to start with, so the daily penalty doesn’t feel as bad.

I’m sorry that you’re unhappy and decided to sell your Model X. Perhaps it’s for the best.

Question before you get rid of the vehicle. How long does it take for the rear vents to blow warm air with the temperature set to HI and the fan set to 3 or 4? I’m only talking about the rear system, here, not the front.