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Old 30th August 2012, 15:59   #91
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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Any particular reason for this, I always downshift from 5th to 3rd to 2nd as I reduce speed gradually when I spot a speedbreaker from afar (on highways) letting the car decelerate rather than braking hard at the last moment. Thought this was a safer way of reducing speed...

Please bear with me for this, views expressed are my personal opinion.
1.Engine braking to prevent the car from accelerating(while going downhill) is mandatory and saves your brake pads from incineration.
2.Downshifting is important to keep the engine in its power band to get maximum acceleration when needed.
3.Engine Braking+downshifting to retard the car is more effective because of Optimal Friction Brake force+ Engine Brake Force.
I still avoid engine braking because downshifting is the tricky part where you rev match using right leg heel-toe technique(toes on brake pedal and heel on accelerator to match RPM without skipping on the brakes).
Failure to rev match or downshifting to proper gear would result in premature transmission synchronizer cone wear, in addition to premature clutch plate wear. If the engine is redlined often while downshifting, driveline assembly can fail.
On the contrary, brake pads being regular maintenance items, replacement is easier on the wallet.
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Old 30th August 2012, 16:44   #92
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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I still avoid engine braking because downshifting is the tricky part where you rev match using right leg heel-toe technique(toes on brake pedal and heel on accelerator to match RPM without skipping on the brakes).
Failure to rev match or downshifting to proper gear would result in premature transmission synchronizer cone wear, in addition to premature clutch plate wear. If the engine is redlined often while downshifting, driveline assembly can fail.
On the contrary, brake pads being regular maintenance items, replacement is easier on the wallet.
does the heel-toe technique require one to depress the brake and A- pedal simultaneously? the technique I follow to downshift (whether to engine brake or for an overtaking manoeuvre) is to take foot off A pedal-depress clutch-slide gear stick to neutral-quick blip of the A pedal to match revvs-slot stick to intended gear-release clutch (i try ofcourse to do this in one seamless motion but still far from perfect). Things get complicated of course if one has to brake as well
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Old 30th August 2012, 20:07   #93
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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does the heel-toe technique require one to depress the brake and A- pedal simultaneously?
Yes you are correct. While braking hard(and using engine braking),to achieve effective retardation, you shouldn't lift your leg from the brake pedal. While having the brake pedal pressed by right leg toe, the heel is used to raise engine RPM while downshifting. It also prevents wheel lock when downshifting.

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the technique I follow to downshift (whether to engine brake or for an overtaking manoeuvre) is to take foot off A pedal-depress clutch-slide gear stick to neutral-quick blip of the A pedal to match revvs-slot stick to intended gear-release clutch (i try ofcourse to do this in one seamless motion but still far from perfect)
That according to me should be absolutely fine. Unless an extreme braking scenario is encountered.
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Old 30th August 2012, 22:34   #94
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

I have seen a lot of people who shift early, and stay in a higher gear even when slowing down, to aid fuel efficiency. How safe is this for the vehicle ? Every engine operates best at around the RPM it makes peak torque right ? So aren't shifts (if required) to maintain that RPM good for the engine's longevity ?
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Old 31st August 2012, 20:00   #95
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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I have seen a lot of people who shift early, and stay in a higher gear even when slowing down, to aid fuel efficiency. How safe is this for the vehicle ? Every engine operates best at around the RPM it makes peak torque right ? So aren't shifts (if required) to maintain that RPM good for the engine's longevity ?
This is an absolute no no, one would end up 'lugging' the engine reducing its life. Drive in the optimum power band (1.5 - 2.5 k) and your FE will hit the sweet spot
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Old 31st August 2012, 21:18   #96
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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This is an absolute no no, one would end up 'lugging' the engine reducing its life. Drive in the optimum power band (1.5 - 2.5 k) and your FE will hit the sweet spot
Thanks for confirming this. I know many, both 2-wheel and 4-wheel users who behave like the 1st gear (and sometimes the 2nd gear) is just a useless addition to their vehicle. I was one of them and used to upshift to 4th gear on my bike @ 20km/hr itself. Now I'm saner.
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Old 13th December 2012, 13:27   #97
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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This is an absolute no no, one would end up 'lugging' the engine reducing its life. Drive in the optimum power band (1.5 - 2.5 k) and your FE will hit the sweet spot
How about the cold starts on cold & foggy mornings. On such days (which are in a plenty over here in Delhi ) i try not to cross 2K rpm for at least the first 2-3 Kms, Up-shifting at 2K rpm results the engine being at about 1200-1300 rpm range in the next gear. Am i doing something wrong on cold starts ?? Should i continue in a gear till something above 2000 rpm so that the engine ends up at about 1500 rpm in the next gear, or alternatively should i continue in say 4th gear till the engine gets warmed up enough for me to avoid lugging??

Would appreciate a word of advice on this one.
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Old 13th December 2012, 15:32   #98
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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How about the cold starts on cold & foggy mornings. On such days (which are in a plenty over here in Delhi ) i try not to cross 2K rpm for at least the first 2-3 Kms, Up-shifting at 2K rpm results the engine being at about 1200-1300 rpm range in the next gear. Am i doing something wrong on cold starts ?? Should i continue in a gear till something above 2000 rpm so that the engine ends up at about 1500 rpm in the next gear, or alternatively should i continue in say 4th gear till the engine gets warmed up enough for me to avoid lugging??

Would appreciate a word of advice on this one.
Let the engine idle for a minute or so when you start for the first time in the morning and do not revv the engine till the optimum temperature is reached. As a rule of thumb I do not let the RPM fall below 1.5k but depending on how much low end torque your baby has, you can play it by the ear. Listen to your engine, you will be able to tell if you are making her huff and puff. Sedate driving is the key while ensuring the engine has enough grunt to pull cleanly
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Old 15th December 2012, 10:52   #99
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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How about the cold starts on cold & foggy mornings.
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Originally Posted by hothatchaway View Post
Let the engine idle for a minute or so when you start for the first time in the morning and do not revv the engine till the optimum temperature is reached.
A cold start on a winter morning in Delhi would invariably see an ECM-controlled petrol engine rev up to around 1600-1800rpm for the initial few seconds, before it settles down to 1200-1300 rpm. This boosting up of reves is less prominent in diesels. But you cannot do anything about changing this behaviour, and this is the time that maximum wear and tear happens.

Letting the engine idle for 30-60 seconds after initial start, before engaging gear and driving off, allows the engine oil to circulate properly. If you are parked on level ground or a down slope, moving off after 30 seconds is generally okay. If you are parked where you need to negotiate an upslope immediately after starting, wait a couple of minutes. Better still, try to change your parking slot/direction in which you need to move the car, so that moving off after starting does not involve going up a slope.

As a rule of thumb, it is best not to switch off a cold engine, especially if it is a diesel, after starting it up, until optimum running temperature is reached. Short runs (1-2 km) after a cold start are far more harmful than moving off 30 seconds after starting the car.
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Old 15th December 2012, 11:23   #100
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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A cold start on a winter morning in Delhi would invariably see an ECM-controlled petrol engine rev up to around 1600-1800rpm for the initial few seconds, before it settles down to 1200-1300 rpm. This boosting up of reves is less prominent in diesels. But you cannot do anything about changing this behaviour, and this is the time that maximum wear and tear happens.

Letting the engine idle for 30-60 seconds after initial start, before engaging gear and driving off, allows the engine oil to circulate properly. If you are parked on level ground or a down slope, moving off after 30 seconds is generally okay. If you are parked where you need to negotiate an upslope immediately after starting, wait a couple of minutes. Better still, try to change your parking slot/direction in which you need to move the car, so that moving off after starting does not involve going up a slope.

As a rule of thumb, it is best not to switch off a cold engine, especially if it is a diesel, after starting it up, until optimum running temperature is reached. Short runs (1-2 km) after a cold start are far more harmful than moving off 30 seconds after starting the car.
Thanks for the advice, it helped re-assuring me that i am dealing with my first diesel car in the correct manner. I usually park my Sx4 on a level ground and on 99% of days give it a good 60-70 seconds of idle before gearing off. Just that i am still confused as to how should the drive be for the first 2-3 Kms till the time engine warms up nicely. I usually don't go beyond 2k rpm during this time frame. Up-shifting at 2K rpm results in an rpm of about 1300 odd in the higher gear, i wonder if this is the right way to do it even if i do it only for the initial few kms. Once i am through with the initial few kms, i keep the car in the perfect gear.
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Old 15th December 2012, 11:34   #101
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

TO keep the engine wear minimum, on cold starts it is the best way (as already specified) to let the engine reach optimum temp. This allows the engine from sump to get circulating and warmed up to do its job. There are moments when we can't think of initial warm up of engine, for that one can drive below 1500 till the optimum temp is reached.
One thing more to add is that also while coming to end your drive let the engine idle (turn off all a/c, blower) for 30-60 seconds before switching it off.
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Old 15th December 2012, 17:42   #102
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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One thing more to add is that also while coming to end your drive let the engine idle (turn off all a/c, blower) for 30-60 seconds before switching it off.
Any particular reason for this? Is this after the car is done for the day or lets say after I reach office and know will engage the engine again only in the evening.
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Old 15th December 2012, 17:47   #103
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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Any particular reason for this? Is this after the car is done for the day or lets say after I reach office and know will engage the engine again only in the evening.
It has been told to me by old (experienced) fellas.
After every drive they suggested to do his. Have also seen many people doing this. My bad didn't actually inquired the reason or logic.
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Old 16th December 2012, 00:09   #104
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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Any particular reason for this?
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Originally Posted by Honda Monk View Post
...while coming to end your drive let the engine idle (turn off all a/c, blower) for 30-60 seconds before switching it off.
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Originally Posted by Honda Monk View Post
It has been told to me by old (experienced) fellas.
After every drive they suggested to do his. Have also seen many people doing this. My bad didn't actually inquired the reason or logic.
Simple logic.

1. Leaving the engine to idle for a little while let the upper cylinder and cylinder head cool off a bit and achieve temperatures that are closer to the block, before complete shutdown of the engine. This prevented the cylinder head from developing fine cracks and/or the top piston ring from cracking and/or the head gasket from springing a leak. One needs to remember that even 30-40 years ago, metallurgy and materials science were not as advanced as they are today.

2. In some modern cars equipped with a turbocharger, the turbo needs to cool down and be lubricated a little; otherwise, sudden shutdown of the engine makes them blow bearings or develop vane cracks - but then, most of us have known about this, and the issue has been discussed on the forum earlier (http://www.team-bhp.com/forum/techni...-shut-off.html (Do all Turbos require idling before shut-off?) ; http://www.team-bhp.com/forum/techni...te-idling.html (Turbo's and one minute idling) ).

3. The AC compressor is best shut down and the cabin fan allowed to blow (warmer) air over the cooling coils for a minute or two, before switching off everything. Else, sudden stoppage of air flow over a cold cooling coil makes condensation develop on the fins - the condensation traps dust and allows it to stick to the coils once the moisture dries out - repeated cycles of trapping dust leads to a choked cooling coil sooner than expected.

Hope this explains the reasons for such advice.

Last edited by SS-Traveller : 16th December 2012 at 00:11.
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Old 16th December 2012, 13:40   #105
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Default Re: ARTICLE: Mechanical Empathy | Preserving the Car While Driving

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The AC compressor is best shut down and the cabin fan allowed to blow (warmer) air over the cooling coils for a minute or two, before switching off everything. Else, sudden stoppage of air flow over a cold cooling coil makes condensation develop on the fins - the condensation traps dust and allows it to stick to the coils once the moisture dries out - repeated cycles of trapping dust leads to a choked cooling coil sooner than expected.
Though I had already knew about that turbo charger and A/C thing (through the forum off course). Thanks Traveler for explaining the first point with logic behind. I advise my friends and relatives the same rules to follow to increase engine life.

Last edited by GTO : 17th December 2012 at 17:30. Reason: Please quote ONLY the relevant bits of a post. Quoting an entire long message inconveniences our mobile users
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