Valve Spring Recall Affecting Fuel Economy?
 

Ever since I got my recall work done, I feel like my average mpg went down. Besides the recall, I had them change out the spark plugs and TOB, nothing else. Has anyone else feel their fuel economy taken a slight hit of a few MPG less?
Is this something that needs to be broken in for the mpg to go back up to where it was?

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Are you going by the car computer only or doing your own calculations?
How long has it been since the recall?

If you have done nothing else to the engine and are using stock tune it will take a little while for the computer to re learn.

Going by the computer average mpg. I usually keep my eye on the fluctuating mpg while I'm driving and I noticed this change. It has been about 300miles since I got it back.

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I have a ots tune before the recall. Do you know if they clear the tune as part of the recall?

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I think it's too soon to tell, you've only gone 1 tank since the recall. Keep driving and monitoring.

Checked my records for the two months before and two months after.

2 months before was 3,836 miles @32.60MPG
2 months after was 3,192 miles @32.64MPG

That included changing out the plugs at 136,000 miles for the first time.

The weather has got colder since you had the recall done. You will take a small hit in MPG just from that. There should be no impact on MPG from the work they did.

When I replaced my battery last spring, the in dash average display went down drastically.
It's finally got back to the pretty solid 33.4 I had before only last month.

You're most likely getting the same mileage.
The computer takes quite a while to creep back up with that 0 still in the data set.

I did noticed that I had to do the EULA agreement all over again on the head unit when I got it back. Maybe they disconnected the battery for a while doing the recall?

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You can always reset your MPG data by holding the button down.

My gas mileage dropped significantly because I started driving the car as if it were new to me - hammering every corner I could find as I had just been re-united with an old friend. Are you certain also that you're not driving differently than before? ;)

Haha no I was told not to hammer it for the first thousand miles so I kept it under 4k rpm. It's been hard not to....

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I think I will reset it and see how I fare. Haven't reset since I got it back from the recall.

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If they didn't disconnect the battery before pulling the whole engine out,
I'd have some very scatological invective to share with them.

They told you not to hammer it because after 1,000 miles if the engine blows it's harder to pin the blame on them.

What the... Is that true?

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It shouldn't be. There is a 12mo/12k mile warranty on the work. The dealer that did mine actually told me to go out and drive it hard after the first few days.

Forgive me if I'm a bit jaded :) probably not the whole truth

After more than a thousand miles, my mileage is down maybe .5 MPG. I did get a map update out of it, though nothing was ever mentioned about this. Wonder if other things were done such as an ECU update?

Should I try to reflash my tune? I am using an OFT tuner

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Why not. What do you have to lose?

.5? That is well within the difference expected with cold weather. There is nothing wrong with your car. You don't need to change to tune. It isn't beyond what would be expected and will go back to "normal" when it warms up outside.

No, I get it. I was talking about the satellite map getting a free update, and then wondering if anything else got updated. I'm fine with the outcome so far.

The map is a whole different thing than the ECU. No cross over. There were probably at least a couple of head unit updates they had to do. They just can't seem to master those.

I'm basically the same before and after.

I suggest you check your fuel mileage the old fashioned way - with a pencil and a piece of paper. Check at least 3 tanks full.

Sometimes, those electronic things lie - ;)


humfrz

I check it both ways and find the car calculated MPG is very accurate. That is, assuming that the car calculates correct mileage, which is sketchy, because GPS MPH readings are always lower by 1 or 2 MPH than what the digital speedometer says it is. So, even if your using pencil and paper, you're still relying on the mileage that the car calculates which may or may not be accurate.

HEY, davesrave, I weren't talken to you. I was ah talken to the fellow from NY.

Iffen I was talken to you, I would have :slap: you for ….. for …. just because, you probably weren't using a #2 pencil.

:D


humfrz

The speedometer wouldn't have any correlation to the distance traveled (separate measurements) so it shouldn't impact the calculated MPG.

Also, speedometers typically read high by design. The primary goal is to never read LESS than the actual speed of the car. Most are high by one or two miles per hour but it could be as much as 10%.

Road and Track carried a good article on the subject some time ago.

Good article, Thanks. It would have been interesting, though, if they used their "highly precise Datron optical fifth-wheel equipment" to compare odometer readouts vs actual. I guess I can read between the lines and say if there were an issue, they would have mentioned it.

My fuel economy wasn't affected much, actually improved .2 mpg on the readout.

Does anybody know if there's a break-in period for this recall where you're not suppose to race the car and treat it as brand new, keeping the rpm under 4k?

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Yea that would have been interesting. Odometers are relatively accurate but not 100%. Used to be that they rolled backwards in reverse which is why you could take a hand drill or other tool and literally turn back time (well miles) on a car (pre-70ish I think is when that stopped).

Current ones are more accurate but could be impacted by a change in tire size, just like a speedometer. They are also impacted by tire wear. As the tire wears, it becomes smaller making the odometer reading higher.

If the odometer is based on a 24.6" tire (that is new calculated circumference of a P215/45R17 tire) for every 1/8" of tire tread wear you gain 25 feet of measured ground per odometer mile. That means for every 211 miles you travel your odometer would be +1 mile off.

Now, I'm not sure if odometers are calculated for medium tire wear so that it balances out over time or not, of if some odometers use a different measurementh other than tire rotation and size.

More interesting info, Thanks again. Don't know how they handle tire wear, but my new to me Boxster's computer asks what size tire your running, and weather it's a winter or summer tire.

There's no reason for a break-in. Someone might argue about camshaft journals but I'd call bullshit even if they had been replaced.


I would, however, drive straight from the dealership to a jiffy lube for good measure.

On the service receipt it showed that the oil was change along with the filters. I don't think it needs to be changed again? Or do you think there might be some particulates floating around?

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Dont worry about it.

I should've qualified my opinion by admitting how jaded I am. Lantana's right. Pull the dipstick. If there's enough oil and it looks fairly new, meh.

Yea, I've seen that on some trucks. It would still be marginally impacted by tire wear in theory, but really not sure its enough to matter. Technically, that would impact manually calculated fuel economy as well.

If the odometer calculation is based on new tire circumference, and your MPG was constant, it would "improve" as your tires wear down. Sometime I may look at my mileage, which I have tracked from day one, and see if I can determine a trend up as tires wear, and a reset with new tires.

If the odometer is set on a "medium wear" tire then at full depth the odometer would run slow, reach actual, then run fast as the tires wear.