Help me diagnose possible high wh/mi highway usage

[Genie]

Just a curiosity question from a guy who doesn't know too much. Could the AC compressor have increasing internal friction, causing more power to be used to run it? That doesn't seem as easy to check as dragging brakes, one only needs a remote temperature sensor for that.

Anyway, curious because I'm about to buy a 2018 X to replace my model S. Need to keep up on these things!

I wouldn’t encourage anyone that isn’t experienced to open up the A/C, not for legal or even environmental reasons but failing to properly evacuate and dehydrate the system will be the start of it’s failure. The compressor isn’t likely to just start drawing more power, noncondensibles from improper repair proceedure or an external problem like dirty condensor coil are potential causes.

 

[geordi]

Just a curiosity question from a guy who doesn't know too much. Could the AC compressor have increasing internal friction, causing more power to be used to run it? That doesn't seem as easy to check as dragging brakes, one only needs a remote temperature sensor for that.

Anyway, curious because I'm about to buy a 2018 X to replace my model S. Need to keep up on these things!

It could, and I have seen where electric compressors in other applications (RV units) have drawn considerably more power before eventual failure. But those usually seemed to have reduced performance at the same time, where this one is functioning great. I don't know if there is a fuse that could be blown on the circuit, but I'd imagine there is some form of load breaking system. If that hasn't tripped, then whatever is happening isn't outside of the normal range.

Based on the information available (and I'm going to run a test with the loaner car I have here to compare what I can see on the dash) it would seem that the AC at least is operating normally. That's good news for me, b/c I haven't gotten mine back yet and they are over 5k on the invoice so far. I'd rather not have to add at least another thousand to that!

 

[brainhouston]

Just a curiosity question from a guy who doesn't know too much. Could the AC compressor have increasing internal friction, causing more power to be used to run it? That doesn't seem as easy to check as dragging brakes, one only needs a remote temperature sensor for that.

Anyway, curious because I'm about to buy a 2018 X to replace my model S. Need to keep up on these things!

I think those scroll compressors have max rpm/kW rating
In theory i guess it could but in reality i think you'll just get less freon moved for a certain kW as things wear out
If friction will come into play, it'll destroy itself fairly quickly

 

[brainhouston]

I wouldn’t encourage anyone that isn’t experienced to open up the A/C, not for legal or even environmental reasons but failing to properly evacuate and dehydrate the system will be the start of it’s failure. The compressor isn’t likely to just start drawing more power, noncondensibles from improper repair proceedure or an external problem like dirty condensor coil are potential causes.

I would
Its not a complicated system, one youtube video and u can DIY it.
Just need to vacuum the system, use proper oil (non conductive in this case) and fill proper amount per label.
Having one of those fancy machines makes it piece of cake, doing it with auto parts store supplies is possible but harder.

 

[geordi]

"Auto store supplies" aren't really the issue unless you just don't have any form of vacuum pump. If you have the vacuum pump, even a Harbor Freight unit, then you are already smart enough to have the dual gauge setup - And those aren't even that expensive! I've seen them at HF for like $60, which for the single-car-and-I'm-done type of people, is more than sufficient.

If the system isn't open for more than a few seconds before being capped while you change things, then there isn't likely to be a lot of exchange anyway. Suction it down to at least 28 inches and leave the vacuum running while you get a beer.... And you should be good to go.

 

[ngng]

Yeah its behind glove box i think...

N2itive is for camber, Doesn't affect range, just tire wear.
I was suggesting for sanity check, just to make sure paper agrees with actual wheel measurements.

I can't find a video on youtube but here's how i do it:
View attachment 944788
Red is square dowels (1/2 or 3/4, not sure) and blue is clamps
Go under car, touch to rims on either side, clamp it, then move to opposite side to see the diff, might have to redo depending which side is shorter.

N2 has parts for toe and camber. Toe would affect range, to what degree, I have no idea.

 

[ngng]

OP, can you think of any changes to the vehicle when you noticed the increased energy consumption?

 

[mxnym]

I also noted at the time that there was a bearing noise, which is why I replaced all four bearings.

No joke, several years ago when I replaced the bearings in my last ICE vehicle due to a bearing noise, my MPG got notably worse (maybe 10%) even though the hubs all spun free (with wheels on). I assume you've lifted and spun all four corners to make sure they feel free, but new bearings and new half shafts (which you mentioned elsewhere) both seem like things that might be a bit stiffer than the ones they are replacing. I'm not sure what you'd do about it, and your numbers arguably seem excessive for that, but I'm not sure if you've considered new parts as a potential contributor...

 

[geordi]

It is certainly possible that the new parts were not great quality - I bought from an Amazon supplier so we all know they are made from genuine 100% Chinesium… BUT I’m not convinced that the triple-the-cost units from a service center aren’t from the same supplier.

The application list for these bearings is unknown to me at the moment, but I already know that the electric parking brake has applications in Italian sports cars with horses and cows as mascots…. So there is a history of snatching parts from other manufacturers. If that other application is known, then prices can be compared.

That said, these did seem nice and smooth on install, and the old ones (at least one of them) had a significant howling sound so it was definitely on the way out at the time. I’ve since put nearly 20k on them and this has been a slowly progressing issue…. So maybe there’s something to this. If they failed out this fast though, I’d be significantly disappointed in their lifespan. Let me research the warranty options on that, maybe I can proactively swap them out anyway after this next road trip.

 

[MP3Mike]

It is certainly possible that the new parts were not great quality - I bought from an Amazon supplier so we all know they are made from genuine 100% Chinesium… BUT I’m not convinced that the triple-the-cost units from a service center aren’t from the same supplier.

It certainly could be the bearings. That is one of the things Tesla specifically said that they worked on improving efficiency of on the Raven Model S&X.

 

[ngng]

It is certainly possible that the new parts were not great quality - I bought from an Amazon supplier so we all know they are made from genuine 100% Chinesium… BUT I’m not convinced that the triple-the-cost units from a service center aren’t from the same supplier.

The application list for these bearings is unknown to me at the moment, but I already know that the electric parking brake has applications in Italian sports cars with horses and cows as mascots…. So there is a history of snatching parts from other manufacturers. If that other application is known, then prices can be compared.

That said, these did seem nice and smooth on install, and the old ones (at least one of them) had a significant howling sound so it was definitely on the way out at the time. I’ve since put nearly 20k on them and this has been a slowly progressing issue…. So maybe there’s something to this. If they failed out this fast though, I’d be significantly disappointed in their lifespan. Let me research the warranty options on that, maybe I can proactively swap them out anyway after this next road trip.

Jack the corner of the car up and spin the wheel. Is there resistance? Grab it and shake it? Is there runout? Any noises? If you did the work yourself, what did you take apart?

 

[brainhouston]

It certainly could be the bearings. That is one of the things Tesla specifically said that they worked on improving efficiency of on the Raven Model S&X.

I'd love to see the diff between old n new bearings but i seriously doubt it gains much efficiency..
Bearing is a simple contraption, if its loose or binds it'll destroy itself.. so maybe only grease type could be improved...

Also, circumference of a bearing vs tire is negligible, it has to bind pretty bad to create much resistance, if it was you'd already know about it

 

[mongo]

I'd love to see the diff between old n new bearings but i seriously doubt it gains much efficiency..
Bearing is a simple contraption, if its loose or binds it'll destroy itself.. so maybe only grease type could be improved...

Also, circumference of a bearing vs tire is negligible, it has to bind pretty bad to create much resistance, if it was you'd already know about it

Along with lubrication viscosity there is ball spacing, diameter, count, material, deformation, preload, interface geometry.

Same types of issues in the CV joints.

Could do a coast down test in neutral to compare rolling drag against other people's cars (or back calculate drag).

 

[ngng]

I'd love to see the diff between old n new bearings but i seriously doubt it gains much efficiency..
Bearing is a simple contraption, if its loose or binds it'll destroy itself.. so maybe only grease type could be improved...

Also, circumference of a bearing vs tire is negligible, it has to bind pretty bad to create much resistance, if it was you'd already know about it

Definitely an over simplification. I ran a set of Auto Zone specials in my Spec Miata because I blew a corner out during a race weekend and they didn't last a month. A bad bearing can manifest itself in a lot of ways

 

[geordi]

It certainly could be the bearings. That is one of the things Tesla specifically said that they worked on improving efficiency of on the Raven Model S&X.

I'd be interested in knowing what (if anything) they were able to work out to get a better bearing.... My experience with them on multiple vehicles is that a sealed knuckle bearing is kinda an either/or device. It either works.... Or it doesn't. Grinding / grumbling / howling, and they need a change out.

Jack the corner of the car up and spin the wheel. Is there resistance? Grab it and shake it? Is there runout? Any noises? If you did the work yourself, what did you take apart?

Not a lot to it - these are really easy to change in about 15 minutes each. Pull the wheel, brake and disc... Go at the back of the knuckle with a socket and a couple extensions. For the driven wheels, a 36mm deep socket and an impact gun. Spin the nut off the axle, pull (or beat on with a BFH) the knuckle off the carrier. Installation is the reverse. I butter the splines of the axle with aluminum anti-seize before it goes into the knuckle, makes the removal MUCH easier. But on this versus my Jeeps (same basic design), these had almost no corrosion welding at 100k miles. Very impressive.

FYI: I haven't seen / heard any evidence of bearing issues, but the supplier on Amazon says they have a 10 year warranty.... So I'm exploring that anyway.

I'd love to see the diff between old n new bearings but i seriously doubt it gains much efficiency..
Bearing is a simple contraption, if its loose or binds it'll destroy itself.. so maybe only grease type could be improved...

Also, circumference of a bearing vs tire is negligible, it has to bind pretty bad to create much resistance, if it was you'd already know about it

Yeah, I'm with you. If the new version was compatible (don't see why not, honestly unless they moved the bolt holes to complicate the design) it would be interesting to know what they changed to make them better. It's a sealed bearing, there's not a lot going on there.

 

[ngng]

Re: reinstallation. Confirming you used a reliable torque wrench to verify the axle nut? Over torquing will cause premature failure.

 

[geordi]

Re: reinstallation. Confirming you used a reliable torque wrench to verify the axle nut? Over torquing will cause premature failure.

If I did anything, it would likely be not enough torque - I used the impact to spin it back on, but only for 3 impacts once it actually contacted the bearing face. I put probably around 80 lb-ft on it. I don't understand why they want so much because it is a splined socket and there is no force against that nut. You are only trying to keep the axle from falling out the back, and there isn't any force trying to do that either. Even with the nut completely off, the axle wouldn't come out the back without taking the bearing out.

But with the new half shafts on it now, the torque is presumed correct b/c the service center just did it a bit ago.

 

[brainhouston]

Over torquing will cause premature failure.

Doubt it ..
Torque matters for tapered bearings but these are not.

 

[mongo]

Doubt it ..
Torque matters for tapered bearings but these are not.

Unless you deform the bearing.

 

[ngng]

Doubt it ..
Torque matters for tapered bearings but these are not.

That's incorrect