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Old 05-31-2014, 12:05 AM   #11 (permalink)
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I routinely drive in 5th gear on city streets in the range of 600-1000 RPM and have had no issues. The problem comes in high load situations at < 1000 RPM's. In this situation the oil pump may not provide enough volume to maintain the film that protects the engine from excessive wear. At higher RPMs under high load the lubrication is not really a problem.

The other part of it is pinging/detonation issues. Back in the days before computer controlled ignition you would have to worry about "lugging" but in modern engines with knock sensors and O2 sensors you really never have to worry about ignition/fuel related problems.

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Old 05-31-2014, 01:46 AM   #12 (permalink)
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Same here. I shift to 5th at 30 & then maintain unless I'm climbing a steepish hill and/or trying to accelerate more to better blend with traffic (like a freeway on-ramp). 30 mph in 5th is about 1350 rpm in my car. In previous tests, that showed as my best mpg speed too (70 to 72 mpg in 2-way tests)
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Old 05-31-2014, 02:23 PM   #13 (permalink)
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I use 5th gear in the S10 down to about 30mph or so to maintain speed or cruise. This is also my highest mpg window for this vehicle as well (55ish mpg in testing). No problem as long as you are not lugging it or putting a heavy load on the engine. When I encounter a hill or need to accelerate, I just shift into 4th (or 3rd if the incline warrants it) until I can shift back into 5th.

Engine is fine (including oil pressure) at 157,000 miles. I did torch a transmission last year, but I'm sure towing a trailer, at or slightly beyond the recommended tow weight for thousands of miles, and my wife learning to drive a manual were the culprit. Actually I'm 95% sure my wife was the culprit, but I would never tell her that.

Short answer, use 5th gear whenever possible...get better mileage.
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Old 05-31-2014, 03:25 PM   #14 (permalink)
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I sometimes run 6th gear down to 20 mph. If I'm in stop and go traffic, and on flat road, I might slip into 6th and just let the car idle along. It might dip to 900 rpm briefly, but I maintain 1000 rpm or above generally.

As you said, you aren't accelerating in top gear at low speeds, so all is fine. The stress on the engine is very low at those slight throttle openings.
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Old 06-02-2014, 10:06 AM   #15 (permalink)
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If you're in top gear below 1000 rpm, you're basically not using the engine for much of anything. That's a good time for it to be off, or at least in neutral down at 700 rpm.
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Old 06-07-2014, 07:06 AM   #16 (permalink)
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^^ what PaleMelanesian said. Maybe my engine is old and grumpy or maybe my car just has way less noise insulation than usual, but it will make unhappy noises below 1300rpm in 5th even if I'm just rolling along. I used to chug along at 25mph, 1400rpm, trying to keep the speed just right, and then I realized my mpg would be better if I just pressed in the clutch and let it idle at 700rpm instead, using 4th gear to give it a boost occasionally.

If anything, pulse and glide at lower speeds is better since you don't have massive air resistance slowing you down quickly.
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Old 06-10-2014, 10:18 PM   #17 (permalink)
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Quote:
Originally Posted by PaleMelanesian View Post
If you're in top gear below 1000 rpm, you're basically not using the engine for much of anything. That's a good time for it to be off, or at least in neutral down at 700 rpm.
I need the engine on to maintain speed or coast down/accel down a hill to get up another. I really don't have a good place for engine off coasting as far as safety is concerned.

30mph puts me right at about 1000rpm anything below that and ill shift to a lower gear. I do alot of engine on coasting.

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