Sudden MPG drop

[Grady]

Originally Posted by Dadhawk

There is a definite difference between winter and summer blend fuel. Here is the average by month for the history of my car. The dips occur consistently in the winter but 90% of my driving is the exact same route. That does not change per month.

Now that is some data!

[nextcar]

Originally Posted by johnnybaboon

I bought my FRS in 2013 and for the first few years I was happy getting ~23 mpg almost all city driving. I calculated it myself after every refuel. One day it dropped to ~18 and has been the same ever since. After a couple years of this, I took it to the dealer and they used a scan tool and said everything was in range. I just fueled up yesterday and got 17 MPG on this tank and it's driving me crazy.

Is there an issue that wouldn't show up on the scan tool or something I should look into to figure this out?

Tires are aired to specs. I've gotten all recommended maintenance. Driving habits haven't changed.

Thanks for any suggestions.

Any chance that your drop in mileage corresponds to a change in tires/wheels?

I personally observed changes in milage when I ditched the primacy tires and then again when I changed rims...

Almost everyone I know never replaces the original tires with another set of OEM tires.

Tires/wheels make a big difference in both handling and mileage in these cars.

[Dadhawk]

Originally Posted by nextcar

I personally observed changes in milage when I ditched the primacy tires and then again when I changed rims...

A tire change was my first thought as well. Stickier tires could reduce mileage a decent percentage point. A change in your route or driving habits could as well.

Mine did not change signficantly when I bought new tires, but that's because, while I didn't stick with Primacy, I did get a similar all-season touring tire rather than a "sportier" tire.

[Busybee]

Originally Posted by Dadhawk

A tire change was my first thought as well. Stickier tires could reduce mileage a decent percentage point. A change in your route or driving habits could as well.

Mine did not change signficantly when I bought new tires, but that's because, while I didn't stick with Primacy, I did get a similar all-season touring tire rather than a "sportier" tire.

I guess all this info here will change my decision for the coming tire selection. I was almost set for sticky PS4S for my daily. May be I should consider PSA/S3.
I am set for the Michelin. Any recommendation from Michelin users? Car is daily and stock. Don’t want to loose any comfort but better (if possible) is preferred


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[N1rve]

Originally Posted by Busybee

I guess all this info here will change my decision for the coming tire selection. I was almost set for sticky PS4S for my daily. May be I should consider PSA/S3.
I am set for the Michelin. Any recommendation from Michelin users? Car is daily and stock. Don’t want to loose any comfort but better (if possible) is preferred


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I had MPS4s and AS3+. Would highly recommend PS4s over AS3+ as PS4s ride better, have more traction, and also is more fuel efficent contrary to popular beliefs.

The AS3+ are warrantied longer though if that matters to you but the MPS4s. If you are on the stock Primacy, AS3+ or MPS4s is more comfortable than the primacy. However PS4s is more comfortable the AS3+ and roadnoise is also lower on the MPS4s than AS3+ due to the softer compound.

I wouldn only get AS3+ if you're on a budget and encounter light snow. Other than that MPS4s is the best. Traction is greatly improved from the MPSS though, I no longer spin tires as often in 1st/2nd gear on my BMW M4.

[Dadhawk]

Originally Posted by Busybee

I guess all this info here will change my decision for the coming tire selection. I was almost set for sticky PS4S for my daily. May be I should consider PSA/S3.
I am set for the Michelin. Any recommendation from Michelin users? Car is daily and stock. Don’t want to loose any comfort but better (if possible) is preferred

Well, they aren't Michelins, but the Bridgestone Ecopia EP422 Plus that I traded out for the Primacies were good enough I bought them again. They are also 60K mile tires if your primary mission is commuting.

[Busybee]

Originally Posted by N1rve

I had MPS4s and AS3+. Would highly recommend PS4s over AS3+ as PS4s ride better, have more traction, and also is more fuel efficent contrary to popular beliefs.

The AS3+ are warrantied longer though if that matters to you but the MPS4s. If you are on the stock Primacy, AS3+ or MPS4s is more comfortable than the primacy. However PS4s is more comfortable the AS3+ and roadnoise is also lower on the MPS4s than AS3+ due to the softer compound.

I wouldn only get AS3+ if you're on a budget and encounter light snow. Other than that MPS4s is the best. Traction is greatly improved from the MPSS though, I no longer spin tires as often in 1st/2nd gear on my BMW M4.

Great info! Thanks

I have gone through almost all topics to figure out my needs. I got my Brz in April 2019 and since then drive every week from Boston to NY (25K). I used the stock primacy summer/winter and 5/32 is left. Soon I will permanently move to NY and want to get another set of rims (summer winter).
Based on my search I settled for 17/8 with the closest offset to stock (most probably I will get Enkei TS5 - 17/8 with 45 offset) and want to warp them with the MPS4s (225/45/17). The stock rims I want to keep fo winter and planed to get an all season tire like the AS3+.
I am not an expert and never had separate summer/winter sets. Based on my experience I am not sure if I really will need solid winter tires. My daily commute will be max 15-20 miles.

I decided to have 2 sets but still not sure about the winter. MPS4s should be fine in from mid spring until snowy days.
Will see. Information provided in this forum helps a lot.

Thanks


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[N1rve]

Originally Posted by Busybee

Great info! Thanks

I have gone through almost all topics to figure out my needs. I got my Brz in April 2019 and since then drive every week from Boston to NY (25K). I used the stock primacy summer/winter and 5/32 is left. Soon I will permanently move to NY and want to get another set of rims (summer winter).
Based on my search I settled for 17/8 with the closest offset to stock (most probably I will get Enkei TS5 - 17/8 with 45 offset) and want to warp them with the MPS4s (225/45/17). The stock rims I want to keep fo winter and planed to get an all season tire like the AS3+.
I am not an expert and never had separate summer/winter sets. Based on my experience I am not sure if I really will need solid winter tires. My daily commute will be max 15-20 miles.

I decided to have 2 sets but still not sure about the winter. MPS4s should be fine in from mid spring until snowy days.
Will see. Information provided in this forum helps a lot.

Thanks


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If you have a dedicated set of winter rims (stock OEM), you might as well get dedicated winter tires instead of all seasons. I am not sure how winter gets in New York though and what kind of snow/how much snow you would get.

[johnnybaboon]

Originally Posted by Busybee

Was the ~23 mpg same during winter and summer ?
I have a noticeable change between summer and winter. Did you check every fueling or from time to time.


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Yes it was consistent. Fluctuation was +/- 1 mpg. I calculated after every fuel up.

Originally Posted by Dadhawk

There is a definite difference between winter and summer blend fuel. Here is the average by month for the history of my car. The dips occur consistently in the winter but 90% of my driving is the exact same route. That does not change per month.

My chart would look something like this
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Originally Posted by nextcar

Any chance that your drop in mileage corresponds to a change in tires/wheels?

I personally observed changes in milage when I ditched the primacy tires and then again when I changed rims...

Almost everyone I know never replaces the original tires with another set of OEM tires.

Tires/wheels make a big difference in both handling and mileage in these cars.

I didn't replace the tires until 2 years after this started happening.

[Dadhawk]

Originally Posted by johnnybaboon

My chart would look something like this.

Yea I realized that after I responded to the post about fuel, which made me think of tires, which you also said it can't be.

I'm at a loss to explain it then. The only other things (besides some kind of mechanical issue or your neighbor siphoning gas out of your car) would be a change in driving habits or routes, but I believe you stated it is neither of those.

[johnnybaboon]

Originally Posted by Dadhawk

Yea I realized that after I responded to the post about fuel, which made me think of tires, which you also said it can't be.

I'm at a loss to explain it then. The only other things (besides some kind of mechanical issue or your neighbor siphoning gas out of your car) would be a change in driving habits or routes, but I believe you stated it is neither of those.

Lol I park in the garage, so I don't think it's being siphoned. And yeah my driving habits have not changed. My route has changed, but not significantly.

[why?]

Originally Posted by Busybee

Great info! Thanks

I have gone through almost all topics to figure out my needs. I got my Brz in April 2019 and since then drive every week from Boston to NY (25K). I used the stock primacy summer/winter and 5/32 is left. Soon I will permanently move to NY and want to get another set of rims (summer winter).
Based on my search I settled for 17/8 with the closest offset to stock (most probably I will get Enkei TS5 - 17/8 with 45 offset) and want to warp them with the MPS4s (225/45/17). The stock rims I want to keep fo winter and planed to get an all season tire like the AS3+.
I am not an expert and never had separate summer/winter sets. Based on my experience I am not sure if I really will need solid winter tires. My daily commute will be max 15-20 miles.

I decided to have 2 sets but still not sure about the winter. MPS4s should be fine in from mid spring until snowy days.
Will see. Information provided in this forum helps a lot.

Thanks


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Unless you are going to new york city where you will not need to drive the car, you want winter tires. You can get General Altimax artic from tire rack on inexpensive wheels so you can swap them yourself. No reason not to do it that way. The car drives awesome in snow on winter tires, and sort of scary on all seasons.

[johnnybaboon]

Update: It was very likely a bad O2 sensor. I took it to another mechanic and he told me the same as the dealer that the computer didn't show anything wrong. One of the things I found consistently when searching online was that a bad O2 sensor could cause a 20-30% drop in mpg. Since that's what I was seeing I asked the mechanic about it and he said it was possible. He said if I wanted to change it out to buy the part and bring it back in and he'd do it for me.

He just finished and showed me the old one and said it was running rich so that was probably the problem. I just filled up and I'll know in a couple weeks when I go through this tank if that fixed it.

[gravitylover]

Originally Posted by Busybee

Great info! Thanks

I have gone through almost all topics to figure out my needs. I got my Brz in April 2019 and since then drive every week from Boston to NY (25K). I used the stock primacy summer/winter and 5/32 is left. Soon I will permanently move to NY and want to get another set of rims (summer winter).
Based on my search I settled for 17/8 with the closest offset to stock (most probably I will get Enkei TS5 - 17/8 with 45 offset) and want to warp them with the MPS4s (225/45/17). The stock rims I want to keep fo winter and planed to get an all season tire like the AS3+.
I am not an expert and never had separate summer/winter sets. Based on my experience I am not sure if I really will need solid winter tires. My daily commute will be max 15-20 miles.

I decided to have 2 sets but still not sure about the winter. MPS4s should be fine in from mid spring until snowy days.
Will see. Information provided in this forum helps a lot.

Thanks

Go with dedicated winter tires like the Conti EWC or similar. The roads here (50 miles north of midtown Manhattan so not far north at all) get scary in the winter, not often but often enough that you need them. After 5 years with dedicated winter rubber I didn't get another set last year and the one time I got caught out and had to drive home in the snow was one of the most challenging rides I've ever had. I actually couldn't get all the way home and had to leave the car at a train station lot and take a cab and that was on tires that reviews say are better than just acceptable in the snow, they are all WRONG. The other thing about those MPS's is they will be pretty terrible when the temps are below 40* especially if it was colder overnight even if the pavement is completely dry.