Valve Spring Recall Affecting Fuel Economy?

[humfrz]

Originally Posted by davesrave

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 you for ….. for …. just because, you probably weren't using a #2 pencil.




humfrz

[Dadhawk]

Originally Posted by davesrave

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.

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.

[davesrave]

Originally Posted by Dadhawk

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.

[radroach]

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

[jc7993]

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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[Dadhawk]

Originally Posted by davesrave

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.

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.

[davesrave]

Originally Posted by Dadhawk

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 measurement 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.

[Ultramaroon]

Originally Posted by jc7993

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?

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.

[jc7993]

Originally Posted by Ultramaroon

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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[Lantanafrs2]

Dont worry about it.

[Ultramaroon]

Originally Posted by jc7993

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?

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.

[Dadhawk]

Originally Posted by davesrave

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.

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.

[gravitylover]

Originally Posted by Dadhawk

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.

My observation over the last 100k or so is that the speedo is spot on when my tires are new and gradually goes to about 2 over as they wear. My mpg also goes down as the tires wear. I figure the correlation is, because they're registering slightly higher miles traveled it manifests itself in speed and mpg being off by that percentage. I wouldn't mind finding the right tire size so that it's both over and under so it's more accurate.

[Dadhawk]

Originally Posted by gravitylover

My observation over the last 100k or so is that the speedo is spot on when my tires are new and gradually goes to about 2 over as they wear. My mpg also goes down as the tires wear. I figure the correlation is, because they're registering slightly higher miles traveled it manifests itself in speed and mpg being off by that percentage. I wouldn't mind finding the right tire size so that it's both over and under so it's more accurate.

I looked at mine, the 20 tanks of fuel before new tires, and the 20 tanks after it. Before was 6747 miles @ 33.41MPG, after was 7034 miles @ 32.72MPG.

It was the same tires, with the old tires having over 69,000 miles on them so they were just above the wear markers. Really though the change isn't significant and varies about as much as any randomly selected 20 measurements in my list. Time of year, driving variances could explain it as easily as tire wear.