Warning: Bad to bump start and skip gears

[budomove]

Posted these questions on HT and got the following response.
Just a heads up.



Is it bad to shift from 1st into 4th, assuming you are not revving 1st too high. My gears are really long...4spd std?

I recommend either shifting to neutral and letting out the clutch to rev match fourth gear or push in the clutch, shift 2-3-4, and let out the clutch. It is easier on the synchros.

Is it bad to coast in neutral?

It is OK to coast in neutral. Make sure the clutch is out to keep the input shaft spinning. This ensures lubrication. I usually coast for shorter periods by depressing the clutch with the transmission in gear. For longer periods, I shift to neutral.


Is it bad to coast with engine off, and bump start?

Don't bump start. You can really stress the axles. If you do bump start, use the highest gear. Coasting with the engine off also cuts your engine lubrication. So, you are restarting each time. It is not as bad as a cold start, but I don't recommend it.

[SVOboy]

Def rev match if you're doing anything serious with rpm changes, that's my rule. And we always try to bump start in the highest gear anyway, I've never felt it to be a stressful event when I've done it. And the neutral advice makes sense, don't want to wear the throwout bearing with the clutch in.

[JanGeo]

Shifting from 1st to 4th or 5th is ok if you let the engine rev down a bit - there is enough drag on the clutch that the slower engine speed will also slow the clutch disk down and just pause in neutral before going into the next gear. With the Clutch pressed in the clutch disk spins at the speed of the car times the gear ratio that you are in. Going fast and putting it in first gear really spins the clutch disk and the throwout bearing. It can explode the clutch disk if you are going too fast. Throwout bearings usually don't wear out much anymore as better ones are being used now. Most of the gears are turning from the axle end and they are located low in the gear box and throw a lot of oil around to lubricate everything. The input shaft not turning is not a problem. The bump starting is turning the crank from the center and is even easier on the main bearings than the starter BUT it is a start without oil pressure so there is unlubricated wear going on for a fraction of a second and probably with HOT oil which is thinner than cold oil but there could also me more of it? Don't pop the clutch too fast either as it does load the axles and CV joints and use higher gears at higher speeds as you already know.

[philmcneal]

Don't bump start. You can really stress the axles. If you do bump start, use the highest gear. Coasting with the engine off also cuts your engine lubrication. So, you are restarting each time. It is not as bad as a cold start, but I don't recommend it.

hm... interesting my axles get banged when i bump start at really low speeds like 15 km/h or 10 km/h in 2nd or 3rd sometimes. 4th I rarely get a bang and 5th is usually smooth but sometimes rev goes a little to high. So far 4th has been very good to me....

but that means i'll have to bump start when my speed gets below 30km/h... then idle drats! Aw man a few mpg or a new axle Ill dedcide hMMMMMMMMMMMMM

as for lubrication that's what synthetic mobil 1 0-20w oil for hybrids are for! Works for regular cars that support 5-20 like mine but I yet have to make the switch!

plus I heard putting it in your tranny fluid gives it boost too! maybe more silky bump start?

[SVOboy]

With my project I'm using 5w20 (down from 5w30) for the time being, until I can find some 0w20,

Anyway, phill, you can get autozone remanufactured axles with a liftime warranty so you can break as many as you want,

[krousdb]

Originally Posted by SVOboy

With my project I'm using 5w20 (down from 5w30) for the time being, until I can find some 0w20,

I have a stockpile of 0W-20. I might be able to spare some for you are interested.

[cheapybob]

Originally Posted by krousdb

I have a stockpile of 0W-20. I might be able to spare some for you are interested.

I tried changing to 1/2 5w-20, but it had no effect on MPG that I could tell

[philmcneal]

since this threada bout the fear of bump starting i'll add to other people's remarks

Even if your tires do not blow up on you, they will wear in the middle in no time. In any size, at any cost, it takes more to replace tires then what you save on gas.
Your engine works outside of the designed temperature envelope, which means fouling everything- from spark plugs to your catalytic converter. Plus, your oil probably has never get to operating temperature (it takes much more time for the oil to get warm then the coolant). You do not ever burn the moisture and fuel contamination out of your oil. That means the sludging possibility is eminent, even with synthetic oil.
Re-starting the engine as often as you do increases the oil contamination by the fuel and removes vital lubrication layer from the cylinder walls.
Your exhaust will rust out very fast too because the water condensation there does not ever burn off.
It is not quite safe to switch the automatic transmission from D to N while driving. Depending on conditions you might as well switch into R with all the consequences.
As was mentioned before, you lose ABS, EBD, power steering and get a strong possibility of the steering wheel lock-up.
I have the ScanGauge as well. As much as I like it for everything else, it is not as accurate in measuring the fuel consumption as "at-the-pump" method. I log both every fill-up, and the SG readings are usually off by more then 10%, no matter what engine size you set in SG.
To me, some of your tips totally make sense, although many are just not helpful, and some are quite dangerous.

hmmmmmmmmm svoboy i didn't know axels were that cheap to begin with haha.

[JanGeo]

Saving a few mpg Yeah you know the amount of money you save in 50,000 miles of driving if you get 3% more MPG with higher pressure is about $100.00 if gas is $3.00 a gallon and you get about 40-45mpg. Is it worth the ride quality loss . . . hummmm I wonder. The tire wear should be a little less with higher pressure however but then you have the extra wear and tear on the suspension components from the hard drive. Makes me think a little . . . hummm.

[SVOboy]

hmmmmmmmmm svoboy i didn't know axels were that cheap to begin with haha.

Think it's like 60 each with a lifetime warranty for my car.

[SVOboy]

I have a stockpile of 0W-20. I might be able to spare some for you are interested.

I need about 6 quarts to do my engine/tranny, so I'll just find it myself and not bum it off you.

[Ryland]

I've alwas been told that bump starting is ideal, because it's less stress on the engine then useing the starter, and that having the engine turning befor it's under load alows oil to be pumped thru it to vital parts preventing as much wear, of course if you were doing it alot, it might be a good idea to get an electric oil pump to flip on for a few seconds befor/as you start the car.

[philmcneal]

Originally Posted by Ryland

I've alwas been told that bump starting is ideal, because it's less stress on the engine then useing the starter, and that having the engine turning befor it's under load alows oil to be pumped thru it to vital parts preventing as much wear, of course if you were doing it alot, it might be a good idea to get an electric oil pump to flip on for a few seconds befor/as you start the car.

how much is a lot? like 8 to 10 a lot on a 15 minute trip?

You know what sucks? I asked 3 mechanics that has been fixing cars for 20 years at least and even they don't have a real answer to bump starting.

Such a shame is it? THAT"S WHY I"M THE GUINNEA PIG

[WisJim]

Years ago, my VW Beetle starter quit, and I didn't replace it for 3 or 4 years, and tried to park so I could coast a bit to start it. Never had any problems that I can imagine were related to bump starting. I don't think that it is of any concern.

[Matt Timion]

Originally Posted by WisJim

Years ago, my VW Beetle starter quit, and I didn't replace it for 3 or 4 years, and tried to park so I could coast a bit to start it. Never had any problems that I can imagine were related to bump starting. I don't think that it is of any concern.

I agree. years ago my battery died and I was too poor to get a new one (wouldn't hold a charge). Luckily i lived on a very small hill that was just big enough to give me the momentum to get it started. Unfortunately I didn't work on a hill, so I required a jump for a while.

Those were the days.

Anyway, welcome to the site WisJim. Tell us a bit more about yourself in the Introduction section.

[JanGeo]

What !!! you never push started your cars??

Big motorcycles are fun to do . . . you run along side and then jump on the seat and land hard while dumping the clutch to keep more pressure on the rear tire to keep it from skidding and locking up . . . yeah! Then you realize you forgot to turn on the ignition and you start all over again!

Mechanics are only interested in fixing the engines not figuring out what makes them break - for that you need to talk to an engineer. Every start is a high wear operation, rings and pistons are not moving - metal to metal contact causes wear. This is why having teflon impregnated parts and other metal coating friction reducers are important. It will take years for you to notice the effects but that is the true test - time will tell.

[tomauto]

I am standing behind bump starting as a great way to save gas. On my last tank I acheived 43 mpg. It was great fun.

The least you could do in a manual is coast down the hills in neutral. Over my trip that is what I did. One one of the stints I achieved a decent 41 mpg. All Highway and drafting behind a semi.

[Randy]

I don't think there's anything wrong with bump starting. Cold starts certainly aren't good, but these are warm starts.

I also don't think having oil pressure to start would help much. As long as there's oil in the bearing, it floats as soon as you turn it. There's really no improvement with pressure, because it's exerted from all sides (the wrist pin may be an exception here). The pressure system is for keeping the bearings cool, clean, and well oiled, not to float them.

The driveshaft concern doesn't make any sense. Accelerating in first has to be much more stressful on them. Driveshafts fail mostly from ripped boots or hot-rodding in low gears. Check them often and they'll last the life of the car.

Now, you do loose power steering, possibly power brakes, and you could even lock the wheel if you work at it. I think it's way better to live with this than to freak out when it happens accidentally. People don't seem to grasp that the brakes and steering still work, you just have to work at it. Then again, they're made to be boosted so they're much harder to use than a pure-manual system.

I've just started trying to bump-start, so I don't have much experience. There does seem to be some places where it makes sense to coast down and then re-start instead of just running up and hitting the brakes.

[philmcneal]

the only problem imo is making them smooth, I find the lower the speed, the more difficult to not make the bump less noticeable (you really feel the BUMP) when you try to do it in 2nd I find. And its harder to keep revs low when bumping, I find sometimes when I'm lucky I can score a 1200 rpm bump. That's when its so smooth and the engine is like, "Ah I'm done from my 2 min nap, what's up?" and not even a sound comes into the interior bay instead of a tiny rev and a "click".

Any tips to making it as smooth as possible?

Do you guys have a list of speeds that you'll bump accordingly?

[tomauto]

Well, when I bump start, I never put the clutch out all the way.
When restarting...

Check that ignition is on >
Push clutch in >
Select gear (4th or 5th) >
Slowly ease out clutch until it engages and starts vehicle >
(this is usually about 1/2 way)
Push clutch in again and select highest gear >
Climb hill >

Speeds for starting [bump in this gear]

30 or less (coming to stop) - [3rd]
30 or more (around town) - [4th]
Highway (any speed) - [5th]

Also, when getting back into gear on the highway, try and rev match as best you can.

[tomauto]

Question:
I would like to know some information that came up on another website I have found and have generally agreed with. In one of their threads, they stated that bump starting with manual transmissions would improve the fuel economy. (Engine off = unlimited fuel econ.) To do this they would turn off the engine while in neutral and then selecting a high gear to restart the engine by ‘bumping’ the clutch to restart the car without the starter) I do agree with this fully, and I do practice this technique while rolling down large hills. What I was wondering is the negative effects of practicing this technique on a vehicle? Examples have come up such as: CV Joints, loss of oil pressure, and resulting damage on restarting the engine from lack of oil.

Answer:
"Squirt and coast" is a recognised way to improve economy, and makes clear theoretical sense. There are really three potential problems:

1) While coasting, you have less control of the vehicle - no engine braking down hills, no ability to accelerate suddenly if required, no power steering, and (after a few applications) no servo brakes either. Depending on circumstances, this might or might not be dangerous. Cars that deliberately knock out the engine, like the Prius, use electric assistance for brakes and steering instead

2) Effect of multiple engine restarts. Obviously this is not ideal, due to lack of oil flow etc, but is probably OK as long as the engine is warm (low oil viscosity)

3) Effect of starting engine by "bump starting" not the starter motor. This seems a bit more risky, but is probably all right as long as you feed the clutch in slowly and are in a high gear (so the revs are not too high)

Overall, I suspect it is probably OK, but am not a mechanical expert so can't really be sure. The safety aspect bothers me, though.

Also, don't forget that modern cars completely cut off the fuel on overrun (eg rolling down hills with your foot off the accelerator pedal) anyway, so the added benefit of selecting neutral may not be that much.

[psyshack]

BUMP AND GRIND.... been doing it for years.

[brick]

The loss of power brakes could be overcome relatively easily with a small vacuum pump fitted to a vacuum reservoir (which probably already exists). Turbocharged cars have these, and I'm willing to bet you could source the parts on the cheap. The control system can't be terribly complicated; just a vacuum switch and maybe a relay.

[MetroMPG]

Originally Posted by brick

Turbocharged cars have these, and I'm willing to bet you could source the parts on the cheap.

diesels also use electric vac pumps. as do most EV conversions.

if this is a serious concern of someone who wants to coast ICE off, the parts are readily available in scrap yards or purchased new for doing a retrofit - "Gast" is a commonly used EV pump brand.

[DaX]

Originally Posted by MetroMPG

"Gast" is a commonly used EV pump brand.

We have a Gast Medical Grade Vacuum Pump here at work.

[psyshack]

My brakes stay good on ICE off coast for qiute sometime. ABS stays active. I dont think I need to add a back up vac. system. Ive tested the cars stoping with no vac and I have no trouble laying into the pedal to bring them to a stop.

[Matt Timion]

Originally Posted by psyshack

My brakes stay good on ICE off coast for qiute sometime. ABS stays active. I dont think I need to add a back up vac. system. Ive tested the cars stoping with no vac and I have no trouble laying into the pedal to bring them to a stop.

I think the fortunate thing about having a small car is that the brake booster is optional. On my honda n600 there are no parts available for rebuilding a brake booster any more, so people are just starting to remove them. Luckily the car only weighs 1200lbs

[diamondlarry]

Originally Posted by tomauto

Well, when I bump start, I never put the clutch out all the way.
When restarting...

Check that ignition is on >
Push clutch in >
Select gear (4th or 5th) >
Slowly ease out clutch until it engages and starts vehicle >
(this is usually about 1/2 way)
Push clutch in again and select highest gear >
Climb hill >

Speeds for starting [bump in this gear]

30 or less (coming to stop) - [3rd]
30 or more (around town) - [4th]
Highway (any speed) - [5th]

Also, when getting back into gear on the highway, try and rev match as best you can.

In my Saturn, I use 4th gear down to about 20 for bump starting and 3rd for speeds below 20.

[psyshack]

I use 2,3,4,5 -- 6 if there is one. I dont like to use 1,R. Im not awful smooth about it. Some of them come off perfect some are real bangers.

Theres so much going on with a bump it isnt funny. Speed, the right gear. Did the engine shut down in your favor when you key'ed off or hit a kill switch. is there a valve in the wrong place for the ecu to think thru ?? are your points open or closed ?? is the condensor in the right state of charge or discharge. On and on and on.

Ive never hurt a tranny be it MT or AT and Ive beat more than my share HARD. From big block American Iron to the worst the brits and the usa have ever made. I can share with you what not to do to a tranny but im sure 99% of the folks here arent doing those things to one.

Im a fluids maint. manic! i change oils and lubes and use what I think is the best for the money. That one action and a bit of thinking will do more for the life of a driveline than rev matching, bumping or just flat out parking a car.

I have my 1st two wheel transport still. My 1968 Honda 50 Mini Trail. It still runs. its never been rebuilt. the cam chain is so slack it rattles in the engine. It burns oil and the piston slap is only over shadowed by the cam chain. its a man/auto. just stomp on the shift lever and it still bangs a gear. the rest of the rig is worn out! The tranny is soild!

so dont worry about your trannys. just maint. them and go!!!

psy

[philmcneal]

I can share with you what not to do to a tranny but im sure 99% of the folks here arent doing those things to one.

i want to know!!!

as for tranny fluid, which are your favs psy?