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Old 06-12-2008, 03:32 PM   #1
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Low gears

Hello to all.

My Astra has manual transmition. In order to get better mileage I shift to the next gear as soon as possible, but perhaps I'm doing it too early. If the engine/clutch/transmition makes that strong noise when an inapropriate high gear is shifted does that mean that the wrong gear was selected? Does that increase fuel consumption?

That sound is quite annoying though.

I would like to get your opinion about this. Am I shifting to early to a high gear?

Thank you.
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Old 06-12-2008, 05:22 PM   #2
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First, I'd say not to drive like that if it's that uncomfortable.

Second, take a look at standardshift.com forums. They talk about the real definition of "lugging", how you know if it happens and what consequences result. However, I don't know if it applies to your diesel. Lugging is described as sounding and feeling like someone is using a jackhammer on your engine, and that it's actually heavy pre-detonation, and I'm not sufficiently familiar with diesels to say how that translates to them.

In my gasoline-powered VW, accepting some growl/vibration for lower shifts results in less fuel consumption.
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Old 06-12-2008, 05:40 PM   #3
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Lugging an engine is an old term. In the carburetor days when you lugged an engine you were applying too much load and the accelerator pump in the carb would dump more fuel than you could burn at such low speeds.

Diesels and feedback fuel injection systems down't have the issue of too much fuel for conditions.

that being said I'm not familiar with your particular setup. I would guess that your diesel should be OK at 1200 RPM or more, maybe less if you are just trying to maintain speed instead of accelerating.

it could also be that you have something rattling that is not related to engine load directly, like a loose heat shield on the exhaust system, or something similar.

regards
gary
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Old 06-12-2008, 06:09 PM   #4
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Thank you very much for your comments. I'll be looking for more information.
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Old 06-12-2008, 06:27 PM   #5
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I know what your talking about and I hate it, on my car the manual states for best FE stay in the tallest gear, even at WOT if I put my foot down in 5th gear and I am doing 30mph, they ECU will only dump as much fuel as the engine can burn based on its fuel table I think?

I know guy who luggs his engines, he has killed 3 cars in 4 years through general bad driving, I have a good idea what speed the engine and gears can do before I start to stress things out, get a feel for your car, smoother is better, aborant vibrations are bad.
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Old 06-12-2008, 06:32 PM   #6
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Quote:
Originally Posted by ShadowWorks View Post
I know what your talking about and I hate it, on my car the manual states for best FE stay in the tallest gear, even at WOT if I put my foot down in 5th gear and I am doing 30mph, they ECU will only dump as much fuel as the engine can burn based on its fuel table I think?

I know guy who luggs his engines, he has killed 3 cars in 4 years through general bad driving, I have a good idea what speed the engine and gears can do before I start to stress things out, get a feel for your car, smoother is better, aborant vibrations are bad.
Yes, you're right. My diesel makes to much noise and vibrates terribly when the gear is too low and results in a weak acceleration.
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Old 06-13-2008, 12:11 AM   #7
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I can shift into 5th gear at approx. 30 mph in my car, or 1600 rpm (from 4th). If it ever gives any sort of vibration or loud noise, I immediately shift down to a lower gear. There is no sense in trying to save gas if you don't have a car to drive.
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Old 06-13-2008, 05:49 AM   #8
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KARR I run my VX at 30 MPH in 5th as long as I only need to maintain 30. If I need to accelerate I use a lower gear.

If I need to climb a grade I use a Lower gear.

My car will go 85 MPH at 3000 RPM in 5th (highest) gear. 30 MPh is just over 1000 RPM.

When your car makes noises that are disturbing it's communicating to you the fact that you have exceeded it's confort zone. It's a good idea to listen to that machine.

The RPM's I have posted here may or may not be appropriate fro your car. In many cases you need to develop a feel for what is best. Smaller engines will need slightly higher RPM.

regards
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Old 06-13-2008, 09:07 AM   #9
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You have helped me a lot. I'll be shifting a little latter from now on.

Thank you all.
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