Down Shifting

Messages
463
Location
Palatine, IL
I read a long time ago that downshifting is good for lubrication because the vacume pressure pulls oil into the upper end of the engine. Can anyone comment on this statement? Agree, disagree, is downshifting good or bad? Thanks, DH
 
Messages
8,711
Location
Nothern USA
Simply letting off on the gas does about as much good with less wear and tear on you and the driveline. Just don't do it with traffic around.
 
Messages
824
Location
San Jose area, CA
NO! Not at all. In these days of up rev limiters the fact of the matter is you can still over rev simply by downshifting and or missing a shift. Downshifting if you are preparing for the next transition is the correct thing to do. However downshifting for such tasks as increasing lubrication makes no operational sense. I would not even engine brake if I can help it!!! To properly do a downshift you should be versed in doing double de/clutching and the heel and toe maneuvers.
 

TC

Messages
1,644
Location
California
Trust the engineering that went into your engine's lubrication system to lube the valvetrain, as well as all other parts south of there. As far as slowing a car is concerned, one can either wear out $25 brake pads or a $3,000 clutch and transmission. I'll sacrifice the brake pads and spend the rest on beer! [Smile]
 

Al

Messages
19,251
Location
Elizabethtown, Pa
quote:
Originally posted by TC: Trust the engineering that went into your engine's lubrication system to lube the valvetrain, as well as all other parts south of there. As far as slowing a car is concerned, one can either wear out $25 brake pads or a $3,000 clutch and transmission. I'll sacrifice the brake pads and spend the rest on beer! [Smile]
Amen-dear old dad told me that one time [Smile] In a new vehicle I always try to get off of the gas periodically to get a little oil up into the ring area. And on long trips I do it periodically even on a broken in car. Probably a waste of time and effort. [I dont know]
 
Messages
4,478
Location
Southern California
quote:
Originally posted by DockHoliday: I read a long time ago that downshifting is good for lubrication because the vacume pressure pulls oil into the upper end of the engine.
This part may be partially correct. The increased manifold vacuum with throttle closed will reverse load the piston rings - a good way to help seat the rings in a new or rebuilt engine. (That's why owners' manuals instruct not holding a steady speed during break-in.) But, going to the extreme of downshifts is unnecessary and could be harmful to both engine and clutch for the reasons listed previously. A drive thorugh hilly terrain, with the attendant frequent accelerator position changes, will accomplish the same thing without bugging the guy behind you on level freeway travel. As for manifold vacuum pulling "oil into the upper end of the engine", I'm not sure I'd agree with that. You have a full-pressure, pump-fed lubrication system that will supply ample oil volume to all moving parts of the engine.
 

Patman

Staff member
Messages
22,003
Location
Guelph, Ontario
quote:
Originally posted by Al: Amen-dear old dad told me that one time [Smile] In a new vehicle I always try to get off of the gas periodically to get a little oil up into the ring area. And on long trips I do it periodically even on a broken in car. Probably a waste of time and effort. [I dont know]
When I first got my licence in 1986, I read Robert Sikorsky's book "Break it in Right-Drive it Forever" and remember that trick on letting off the gas and coasting with new engines. I've done that quite a lot on every new car I've owned since then! And I've never had oil consumption issues on any car that I did that with.
 

DockHoliday

Thread starter
Messages
463
Location
Palatine, IL
Wow, a thread where everyone agrees. I knew it would happen some day! What Patman described is more in line with what I was thinking - nothing radical. On my way home from work, I take an off ramp which ends at a stop light that seems to always be red when I get there (I swear it sees me coming). I usually will leave the car in 4th or 5th gear (6 speed tranny) for the first part of the ramp and let the car gradually slow down. I then put her in neutral and use normal braking as I get close.
 
Messages
605
Location
Mississauga, Ontario
I would have to disagree with the general public.. [Razz] I downshift 80% of the time using the proper heel and toe/rev matching techniques. If you don't practice the above on the street, how can you do it properly on the track? Regardless if you race/lap, it's good to use those techniques anyway as you should always be in the proper gear for the road speed. [ October 09, 2003, 01:57 PM: Message edited by: Quick_lude ]
 
Messages
2,095
Location
IL
Then I would have to agree with quick_lude. In addition, if you know how to shift and use the clutch you are not going to wear anything out significantly faster.
 

DockHoliday

Thread starter
Messages
463
Location
Palatine, IL
I knew the agreement thing would not last with this opinionated group. [Big Grin] What exactly is proper heal/toe shifting? I have read that term in many a magazine article, but never knew exactly what it meant.
 
Messages
8,711
Location
Nothern USA
The multi-tasking driver has his left foot firmly planted on the clutch pedal, the heel of his right foot on the brake and is nudging the gas with the toe of the right foot to bring the revs up to where he can release the clutch after a down shift without excessive wear on the car, passengers, and himself. Having the engine and transmission input shaft at nearly the the same speed makes for much smoother down shifts. Even if the engine is going to do most of the braking, having the foot on the brake pedal lets those in the rear know he is slowing. This also smoothly gets you into a lower gear to accelerate when ready.
 
Messages
29
Location
Spokane WA
I rarely downshift in town to help slow down. Partly because my syncros are gone though. Driving on mountain roads with a long grade I will leave it in 3rd or 4th gear and just use the engines compression to keep my speed consistant. Usually cars infront of me are hitting their brakes every few seconds but the only time I usually have to is around switchbacks. I think its a smart thing to do on really steep grades and especially with snow on the ground.
 
Messages
2,037
Location
North Carolina
I know one thing. Growing up in the mountains of Pa and driving up and down them to and from my grandmothers house with my old 68 Impala with a 250 hp 327 with 88k miles on it, if I let it coast down the mountain, (a 4 mile descent) by the time I got to the bottom it was smoking pritty good out the exhaust. But with normal driving it didn't smoke a lick. Just when I was going down and letting the engine keep a slow ride down using the brakes some as well. That engine had nothing but QS in it from the gentleman I bought it from. When I got it I had the engine rebuilt at 100k, ( was going into the Air Force and wanted to make sure it was dependable) After taking the engine apart I was surprised to see how clean it was inside, espesially with everyone hating QS oil. It had it's little build up around the distributer but nothing really major for a 100k engine with 4k oil changes. I put 300hp heads on it, the double hump ones and a blue printed 300hp crane cam and what a difference it made. But back to the subject at hand. We always used the engine to slow down and never had any problems with anything, drive train nothing and that was in both our standards and AT's. Heck our 72 square back VW made it to 140k before it threw a rod on #2 cylinder and I was told that was a normal thing due to that cylinder not getting cooled like the rest and usually didn't last as long as what we got out of it. Oh and it had the original clutch on it as well.
 
Messages
85
Location
CT
This just came up in a motorcycle group (I think) or some other gearhead group(s) I frequent. They stated that an engine will produce (use) 15% of maximum HP upon letting off the gas at pek power. So If your engine produces say 100 HP, the maximum strain on the engine and tranny would be about 15 HP. Why do you think the jake (sp) brakes are used so much on trucks?
 
Messages
342
Location
Limon, Co
I'll come from the side of the 4x4 nutz. You try coming down The Black BEar(Ouray into Teluride Colorado) with out putting the truck into 1st and low range on the t-case and running it ALL the way down against the engine brake/tranny. I have done MANY such trails in my 83 blazer with a 350 chevy with no ill effects on the motor due to oil circulation. Id rather use up my 3000$ tranny then try and us breaks going down steep grades..
 
Messages
8,711
Location
Nothern USA
quote:
Originally posted by DockHoliday: snip .... I take an off ramp which ends at a stop light that seems to always be red when I get there (I swear it sees me coming). snip ....
Yeah, we have a bunch of those around here too. It today's traffic, you seldom have an opportunity to leave it on cruise control for an hour. When you actually have the road to yourself, backing off on the gas about every hour may be a good idea.
 
Messages
3,332
Location
Bolivia
Using Engine braking will use a little more oil. Care should be taken to synchronize speed in doing so, or you can over-rev the engine or more easily the turbo (if so equiped). One of my sales people did a 4th to 2nd and sent a piston thru both sides of the block. I rarely use downshifting in town, but for much of my driving on 10% grades and steeper, if I didn't use it in the mountains I would have no brakes. When I had my Grand Cherokee I even needed to use 1st (auto-trans)on some mountains in order to not smell and destroy the brakes.
 
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