A little background.

We have an 06 HCH II with around 47,000 miles on it. I was able to routinely get 50+mpg while traveling on all highway trips at around 65mph (generally around 54mpg iirc). Tire pressures were around 37-38 Front and 34-35 Rear. About 4-5 months ago I started to notice that FE was dropping quite a bit, highway trips were much more difficult to get good mileage, at this time I was in the mid 40mpg range. Car also felt a bit more sluggish. I noticed that the OEM tires were on their last legs and wanted to get something with a bit more tread before winter so my wife would be a bit safer driving if she got stuck in the snow. I ended up getting the Michelin Pilot Exalto A/S tires which a few users have commented on being a good tire and no ill effects on FE. I had hoped this would have help out my FE a bit but unfortunately it didn't.

I now have a 60 mile commute each way (about 90% highway) and have really started to notice a hit in mileage. It's almost impossible to get above 42mpg. Same tire pressures, same driving habits, etc as when I was getting the great mileage. Weather is in the 50-70 range and climate control is always in Auto (since we bought the car) at 68-70. The car feels like it is laboring too much and not using the IMA the way it should. I was pretty good at controlling the way it used the assist, regen, glide, etc and now it seems like the IMA system has a bit of a mind of it's own. The other day the battery charge dropped to 1 bar and went into forced regen (I know that this can be normal, it happens ever now and again) and shortly after that the CVT started to act strange. There have been a few instances where the car was under load going up a hill and car engine was running around 3k rpm for a few seconds, under normal circumstances after the car was not under heavy load (or foot lifted off the gas) engine speed would drop back down to 1,500-2,000 rpm range. In these few instances the engine continued at 3k rpm, even though the car was traveling on a flat at 65mph. The engine speed would not drop down to the proper range unless I manually shifted the car into neutral and engaged back into D. As soon as I did that rpms dropped back down.

Has anyone else seen things behave this way? I'm going to probably have an alignment done just to rule that out, but I know what the dealer is going to say if I try to have them look into this. There are too many variables and I know how many dealers work. The other thing that is odd is that there is no CE light so I don't think they'd be getting much information from the ECU...but it is still probably worth trying.

Other info:
Oil changed regularly (per maint. minder) with 0w20 Mobil 1, Trans fluid changed about 10k miles ago, all other fluids are good.

I'm interested to see if anyone else has encountered any of these issues. Thanks,

Jeff

 

There have been a few other posts about this in the last 6 months or so. I did some basic searching and found this:

https://www.greenhybrid.com/discuss/...pm-range-8958/

However, I haven't been able to locate the actual post I'm thinking of. I would suggest a little searching using the advanced search feature (on the peach colored toolbar above) in the HCH general and HCH II forums.

As I recall, it was either a problem with a rotational sensor, something to do with slightly different wheel sizes, or something to do with CVT fluid level (I know pretty vague, but since I haven't had the problem, I didn't pay that close of attention).

 

Thanks for the reply. I did a few searches but didn't come up with anything of value. I think the link that you attached could be part of the issue. I'll do a bit more research on some of the topics in that thread.

Thanks again for the input, I think I'm going down the right path now. It doesn't seem that my issue is quite as bad as the OP's, but the symptoms are definitely very similar (only lower RPM's).

 

Do some research on this site and elsewhere about a rear control arm suspension problem that was widely known to cause premature tire wear and poor fuel economy.

 

Have you compared the weight of your new tires to the weight of the original tires. I was talking to a mechanic at Honda who told me a small increase in weight for replacement tires will have a noticible impact of FE. Just a thought

Jeff

 

The control arms might be causing some FE issues, and I'll take a look into that. I didn't notice abnormal wear on the OE tires. I rotated regularly (every few thousand miles) and always pay attention to these things. When I take it to the dealer I am going to mention this and tell them to replace the control arms since it's a known issue.

This obviously doesn't explain the CVT issue, but who knows...with my luck I'm sure there is more than 1 thing wrong.


I'm almost positive the tires are not the issue, a number of people are using these tires and some were actually seeing an increase in FE. Weight does not have as much of an effect as you'd think, rolling resistance is much more of a factor.

 

My MPG DID go down once I switched from the original equipment Dulops to the Michelin Exaltos. But it was not that big of a hit, and I'm fine with the tire choice. They are FAR better handling and quieter.

I, like Kristian, remember a thread or 3 about this over-revving or revving and staying stuck there. I've never had this issue either, but it sounded like the exact issue you describe.

 

Too much or too little CVT fluid can cause that as well as using Automatic Transmission fluid instead of Honda CVT fluid. Not all mechanics are aware of that requirement.
ATF fluid can cause slow downshifts as the CVT belt is not as well lubricated. ATF is $2.00 quart CVT is $7.00 quart - a cheap mechanic could use it and you would not feel it for about 500 miles.

Follow the instructions in the Owners Manual for checking the dispstick for the CVT, not doing so can show too much and really you have too little.

 

I have a couple of data points that can explain some of your reduction.

1. Your OE tires were worn and smaller diameter than a new tire. If you look at the specs for the OE Dunlops on TireRack.com, you'll see they are 25" in diameter. If you had 90% treadwear, then they were really closer to 24.5". Your Exaltos are 25" if you bought the right size. The net effect is that your indicated FE will be about 2.2% less with the new tires. (The reality being that you are really still using the same amount of fuel to go the same distance, just your car was/is measuring distance incorrectly).

2. Maybe this is the biggest explanation. The Exaltos are 17% (21 lbs vs 18 lbs) heavier than the OE tires (actually, probably the difference is bigger since the OE tire, with wear are less than 18 lbs). As you may have learned in physics class, rotating mass requires much more energy to get up to speed than dead weight. The hybrid helps reclaim some of that energy, but the inefficenies of system are amplified with the additional rotating mass.

Hope that helps...

-dan

 

I did the fluid change...I used CVT fluid and I know it was done right.

1. I mentioned in the first post, mileage was the same w/ the new tires vs the worn dunlops...if it was off 1 or 2 mpg that would be fine but if there was any difference between the two it is negligible.

2. See response to 1 above. As I mentioned before, 3lb is not going to do much of anything for fuel economy. Daily conditions (temp, traffic, etc) will have more of an affect on FE. Of course the lighter tires would help from static conditions but I'd guess these tires might cause a 1-2% hit in FE on the highway due to the weight. I'm an engineer, so I've had my share of physics. In my case approx 90% of my miles are highway already at speed. Rolling resistance will play more of a part in my mileage because that is affecting the distance I can glide down the slopes and maintain speed up hills.


At this point I'm going to try and get the car to the dealer next week to have the control arms replaced, I think that is a good start. It'll have a fresh alignment after that. I'm also going to see if they can anything regarding a reflash of the powertrain control unit (I think that is what solved some of the other CVT issues in the other cars).

I think those two things are a good place to start since they are already documented and I already was planning on getting an alignment.