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Old 05-17-2009, 04:25 PM   #1
Hotsho111
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Default Drop in fuel economy and higher revving

Hey, I just did the 30k on my 07 2.5i (air filter, maf cleaning, tranny fluid change, rear diff fluid change, PCV valve change, coolant change and waiting on plug wires to do those) and driving back to school the car was revving a littler higher than usual (about 2700 rpms at 65mph in 5th gear, versus 2500 rpms at 65 mph in 5th gear before) and the coolant temp was a little higher than usual (about 187 degrees versus about 180 before).

This was the first drive (a 200 mile trip) since the maintenance and fuel efficiency is down to 28 (from 30-33 doing the same speed).

I was wondering if anyone had any suggestions on what may be causing this. Does the ECU just need to recalibrate everything because of the new fluids and parts?

Also no CEL lights after the maintenance.

As a note, the tranny fluid is filled to the full fill level and I put fluid into the rear diff until it started coming out the fill hole. I bought 5 quarts and I still have a quart of fluid left. The specs say 3.7 quarts in the front and .8 in the back so shouldn't I be down more? I did the change on level ground too.
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Old 05-17-2009, 04:45 PM   #2
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reset the ecu to help it learn with the new parts.
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Old 05-17-2009, 05:22 PM   #3
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how can the gearing change, that makes no sense. in a given gear the engine speed will always be the same at any given RPM unless there is slippage in the clutch or the gear ratio has physically changed.

You may not be able to get 100% of the old fluid out of the case/diff so it might not accept the full capacity since it has a little bit left in it. I have never put the full 5 qts of engine oil in, like the main manual says is the total capacity, but about 4-4.3 qts like they main manual says is the filling amount at oil change. The maint manual doesn't give a "@ fluid change" capacity for trans/diff fluid, only total capacity for trans/diff fluid so i would expect not to be able to get 100% of the capacity back in, especially for the trans.
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Old 05-18-2009, 01:00 AM   #4
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Quote:
Originally Posted by Hotsho111 View Post
the car was revving a littler higher than usual (about 2700 rpms at 65mph in 5th gear, versus 2500 rpms at 65 mph in 5th gear before)
Quote:
Originally Posted by RaceFaceXC View Post
how can the gearing change, that makes no sense. in a given gear the engine speed will always be the same at any given RPM unless there is slippage in the clutch or the gear ratio has physically changed.
This.

Except where he should have said "In a given gear, the engine speed will always be the same for a given vehicle speed". I know that's what he was trying to type though.


As far as the mileage change, there's a huge number of things that could be happening, most of them falling under the heading of "random chance". You need a BUNCH of tanks of gas to make any kind of a guess at a real change in fuel economy.
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Old 05-18-2009, 01:41 PM   #5
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Quote:
reset the ecu to help it learn with the new parts.
LMAO!-!-!
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Old 05-18-2009, 02:49 PM   #6
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^ Yeah, I think that's cute too.


You won't get all the fluid out of the tranny and rear diff. Athough it's labeled at 3.7 and 0.8 quart, you just won't get all of the old fluid out. Expect to have some left over.

Ditto on rpm change -> slipping clutch. Generally you can make it slip, not just showing a little different rpm value. However, the rpm and mph is linked, so it's not like they can automatically vary.
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Old 05-18-2009, 03:17 PM   #7
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Any suggestions on why the temp is up?
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Old 05-18-2009, 07:31 PM   #8
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Quote:
Originally Posted by williaty View Post
Except where he should have said "In a given gear, the engine speed will always be the same for a given vehicle speed". I know that's what he was trying to type though.
Yes. Thank you, sir.
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Old 05-19-2009, 12:22 PM   #9
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Ok, so I was wrong about the rpm's, but does anyone know why the car is running hotter?
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Old 05-19-2009, 06:32 PM   #10
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different coolant maybe? less coolant? less efficient coolant? little air in the system? Or making more power so more heat is a byproduct. the 7 degrees higher isnt much... i would just watch it and see if it keeps going up a bit over time then do something about it. Im about to do this same thing, but also will do plugs and not wires. Your fuel economy seem to be normalizing to what you had been getting before?
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Old 05-19-2009, 06:43 PM   #11
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I used the OEM coolant. I think the regular idle temp is a little above the first notch, and mine is right in the middle of the first and second notch.

Before, on this same trip (between home and school), doing the same speed I was getting 30-33mpg (30 doing the whole trip at 70, 33 doing the whole trip at 65, and I went back at like 67 and got 28. This was the first long trip since doing the 30k
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Old 05-19-2009, 07:25 PM   #12
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^ As far as fuel economy goes, it's too little of a difference to tell. Wind by itself can easily cause a +/- 3mpg change. Add to that the relative altitude drop or raise, humidity, and temperature. Unless you anally logged the mpg and average speed using a ScanGauge or something, you simply can't tell.

Temperature: did the thermostat get changed? Maybe your old coolant was all yucky and full of gunk, with a little of a smaller flow around the thermometer, which caused a lower reading
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Old 05-19-2009, 07:41 PM   #13
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The thermostat didn't get changed. Taking an image from STI Sibb at iwsti, the normal temp he has pictured is what mine was at:



and now it is slightly above the middle of between the two so it is noticeable (also the temp gauge I had showed the higher temp too)
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Old 05-20-2009, 01:04 PM   #14
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Isn't the temp gauge on the dash a "dummy" sensor?
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Old 05-20-2009, 01:15 PM   #15
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^ as hell it is.
According to scangauge, under normal driving the temp ALWAYS cycles in between 85 and 93C (185 and 200F). It's just the cycle of the thermostat. Well guess what? the needle doesn't move at ALL.
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Old 05-20-2009, 05:05 PM   #16
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I may be inaccurate, but it was always at the same reading before I changed the coolant, and now it is consistently higher since then
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Old 05-22-2009, 09:17 PM   #17
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any other suggestions on why the temp might be up?
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Old 05-22-2009, 09:34 PM   #18
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driving back to school and 65mph doesnt sound good together
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Old 05-22-2009, 09:36 PM   #19
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Ya, its an extremely boring drive. I did it because on the way home (I really didn't want to get there fast) I wanted to see what kinda fuel economy I could get.

I did it on the way back to see if it would change after doing the 30k

As a side note, I don't suggest anyone drive the speed limit on highways...its probably the most dangerous thing you can do. If you want to know why, try it for yourself
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Old 05-22-2009, 10:01 PM   #20
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Quote:
Originally Posted by Hotsho111 View Post

As a side note, I don't suggest anyone drive the speed limit on highways...its probably the most dangerous thing you can do. If you want to know why, try it for yourself
This makes no sense
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Old 05-22-2009, 10:08 PM   #21
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Try it, everyone else on the road is going at least 10 mph faster then you, and the one person on the highway that is going slower than you, when you have to pass, is like threading a needle (especially if you maintain the speed limit and don't go faster to pass)

You also always end up in people's blind spots because you're maintaining 65 and when you go to pass that one person that's going slower, for some reason, they ALWAYS speed up when you are on the side of them putting you in their blind spot. Mean while, those 20 or so cars that you have backed up are getting annoyed that they have nowhere to go because you're maintaining the speed limit, so you are essentially a rolling roadblock now.

You also notice how inconsistently people drive, speeding up and slowing down all the time

Maybe its just Massachusetts drivers lol

Again, try going on a 100 mile trip with cruise at the speed limit
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Old 05-23-2009, 12:49 AM   #22
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5 qts? of engine oil?

no manual states that .
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Old 05-23-2009, 12:52 AM   #23
Hotsho111
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Not engine oil tranny oil: 3.7 quarts in the front tranny/diff and .8 quarts in the rear diff
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Old 05-23-2009, 12:53 AM   #24
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yea thats 4.5.
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Old 05-23-2009, 12:55 AM   #25
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and???
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