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Old 05-30-2014, 10:20 AM   #1 (permalink)
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low speed high gear

I am wondering if there is any concern with driving in your highest gear at low speeds. For me it's 5th gear at 30-35mph. Let me be clear this is just to maintain speed not accelerate. I wait for downhill to do that then coast for as long as possible. When my minimum speed is reached generally 30mph in town it's back into 5th to maintain.

I've been told on performance minded forums that this stresses the engine way to much and I should be in 4th for my highest gear at that speed. Thing is I tried that and it raised my RPM less than 250rpm but also drops my instant mileage between 7-10mpg depending on speed.

So what's the correct way to do it to ensure as little harm as possible is being put on the engine?

Also I searched around and found various answers from it's fine to you're going to blow your engine to carbon will destroy your valves...

Now I could maybe see the carbon build up.But, I will have a look to verify, I dont believe that would be an issue if fuel is washing the valves proir to entering the chamber. Please correct where I am wrong.

Sorry for the long winded post.

Mods if this is in the wrong spot please move.

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Old 05-30-2014, 10:27 AM   #2 (permalink)
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If you're lugging the engine you could be doing damage. However, if its not lugging or vibrating abnormally you're fine.
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Old 05-30-2014, 10:29 AM   #3 (permalink)
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it's above 1000rpm and it's not vibrating or lugging. If I drop below 30mph it will yes. But above 30mph in 5th it's almost like she's idling.
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Old 05-30-2014, 12:18 PM   #4 (permalink)
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It's only lugging if you demand high output from it. What rpm does it idle at? I'm sure that's well below 1000. As long as you're gentle, anything from idle on up is fine.
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Old 05-30-2014, 12:42 PM   #5 (permalink)
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the engine will let you know if you're in too high of a gear for the output you request(throttle) of it.

foot to floor at 30MPH in 5th? probably a bad idea.
more or less closed throttle at 30MPH in 5th? not a whole lot more load on the engine than idling out of gear.
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Old 05-30-2014, 01:16 PM   #6 (permalink)
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I regularly run my truck down to 20 MPH (650 RPM) in fifth gear, and even accelerate from that speed. No engine problems so far, but I only have 86,000 miles on it.

Although I have to replace the kill switch again this weekend. The shaking of the shift lever destroys the kill switch.
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Old 05-30-2014, 03:19 PM   #7 (permalink)
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Quote:
Originally Posted by RobertISaar View Post
the engine will let you know if you're in too high of a gear for the output you request(throttle) of it.

foot to floor at 30MPH in 5th? probably a bad idea.
more or less closed throttle at 30MPH in 5th? not a whole lot more load on the engine than idling out of gear.
Right I only open the throttle enough to maintian speed to the next down hill. Never floor in those conditions that obviously wouldn't be smart. LOL

and Yea the idle is below 1000rpm I'll look tonight and see but I think it's like 750ish IIRC.


Thanks for the input guys
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Old 05-30-2014, 03:24 PM   #8 (permalink)
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The engine will say it's unhappy when it bucks, protests, or fails to accelerate. Other than that, it's OK.
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Old 05-30-2014, 04:24 PM   #9 (permalink)
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maintaining speed at low low rpm is fine.
although i do try to avoid really high load at sub 1.5k rpm. I worry that high cylinder pressures and low oil pressure will squeeze the oil out of the bearings causing wear.
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Old 05-30-2014, 06:04 PM   #10 (permalink)
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I use 5th @ 1000rpm for 30mph in my car , much lower and it stumbles. I find the need to drive slower then 30 is far and few between , I about never use 4th for more then a quick gear change.

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