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Can under revving cause damage?

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Old 11 February 2011, 11:09 PM
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PPPRob
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Default Can under revving cause damage?

I've got into the habit when in traffic of letting the car coast at 1k rpm but when the traffic clears I pull away. The engine sounds like it's struggling as you'd expect and the car rumbles but am I actually causing any damage (det?) or is it just a little unhappy about doing it?
Old 11 February 2011, 11:13 PM
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99greenwagon
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not being funny, but why would anyone do that?
Old 11 February 2011, 11:18 PM
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Gigsy
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Nothing wrong with coasting at 1000 rpm - tickover is 700-800. Wouldn't recommend pulling away in too low a gear though.
Old 11 February 2011, 11:20 PM
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andy-m
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dunno about the newage, but i know on the classics if your in traffic for a while, you get heat soak from the turbo to your TMIC. if you then suddenly pull away a bit nippy, it causes pinking. usualy, if i am in traffic for any length of time, when i get going again, i keep the revs low and acellerate gently till the TMIC has had some air over it to cool it a bit before i start driving normaly again
Old 11 February 2011, 11:26 PM
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Originally Posted by PPPRob
I've got into the habit when in traffic of letting the car coast at 1k rpm but when the traffic clears I pull away. The engine sounds like it's struggling as you'd expect and the car rumbles but am I actually causing any damage (det?) or is it just a little unhappy about doing it?
You don't say what gear you do this in? In 1st or 2nd it'll be ok but any gear higher than that and you should change down. Actually labouring the engine in a high gear will cause unnecessary loading on the bearings.

JohnD
Old 11 February 2011, 11:27 PM
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Originally Posted by Gigsy
Nothing wrong with coasting at 1000 rpm - tickover is 700-800. Wouldn't recommend pulling away in too low a gear though.
You mean too high a gear?

JohnD
Old 11 February 2011, 11:40 PM
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PPPRob
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Originally Posted by JohnD
You don't say what gear you do this in? In 1st or 2nd it'll be ok but any gear higher than that and you should change down. Actually labouring the engine in a high gear will cause unnecessary loading on the bearings.

JohnD
Thanks John, I suspected it wouldn't be such a good idea but when you crawl in as much traffic as I do it just becomes a lazy habit. I do it in 2nd, 3rd and 4th if necessary!
I do try to accelerate gently after this but clearly the correct way would be to change down and maybe even feed in the clutch too.

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Old 11 February 2011, 11:43 PM
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Gigsy
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Originally Posted by JohnD
You mean too high a gear?

JohnD
Lower in terms of numeric ratio but yes, I meant better to pull away in 1st than 5th ;o)
Old 12 February 2011, 08:27 AM
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dunx
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If the transmission is driving the wheels, the fuel is cut-off, if it's idling it's using fuel.

Not good to labour the engine IMHO.

dunx

P.S. I cruise downhill to work at 40 mph in top gear and it's fine, and sips a mere 16 mpg LOL
Old 12 February 2011, 11:48 AM
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Haven't you read your Impreza Owners Manual
Driving in the wrong gear causes the engine to labour and should be avoided
Old 12 February 2011, 01:02 PM
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Suberman
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kick that habit mate. Like the rest has said, labouring the engine is really not what you want to do too often
Old 12 February 2011, 03:59 PM
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jh1
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was your last car an auto? lol
1k rpm is fine if coasting down hill.
you can tell by the sound of the engine if its happy to pull or not, simply make a note of the revs
Old 12 February 2011, 04:37 PM
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sharpy2010
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Ive heard doing this buggers up the head gasket... whether or not thats correct though is another matter!
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