Engine Off Coasting Damaging My Car?
 

Sometimes I like to turn the engine off if I'm going down a hill and then use the clutch to start the car again instead of putting more wear on the starter, but is that hurting something? Is the sudden jerk of the engine and transmission turning over again damaging something? Should I be concerned? Will having worn out motor mounts make it worse? This is something I have always wondered about but was never able to really find a good answer for. Thanks!
- Aaron

This has been discussed several times if you do a search, but I'll sum it up.

Bump starting is not going to cause excessive wear or other problems if it is done properly. You shouldn't feel a sudden jerk. Essentially you need to double clutch in order to bump start. You should pick the highest gear that it will start in. When you want to bump start, let off the clutch slightly until it grabs, then push back in. Once the motor is running, rev match and let out the clutch to drive in gear.

The only difference between using the starter and bump starting is that one uses the starter to rotate the flywheel instead of using the forward movement of the car to rotate the flywheel.

When I EOC in my truck, I bump start by dropping into top gear and easing the clutch out for a smooth uptake. The truck has finally burned out its clutch, and it only burned out because it's
1) the original clutch from 1987,
2) got over 200,000 miles on it and
3) been teaching the last son how to drive stick. THAT is what killed it more than anything.

Seriously, I've been driving my truck like this for yeeeeaaaarrrrs. It shouldn't hurt anything.

Also sometimes I'll do EOC without taking the truck out of gear, just let your momentum carry the engine along. It keeps your accessories spinning so you don't run out of vacuum for brakes or pressure on the power steering. You lose a lot of distance on your coasts but when you key back on there is no shock whatsoever.

Forced DFCO? :)

It's an '87 and carbureted. Yeah, forced. One click, not two. Two locks the steering = Very Very Bad.

since it's relevant... thought i've had about bump-starting lately is putting the throttle on the floor(or at least, opened significantly) before letting the clutch out to prevent the instant engine braking that would happen with a closed throttle plate when going from 0RPM to whatever the engine would spin up to when in gear.

seems like it would be less strenuous on both the clutch and engine.

Aren't you still using* fuel?

*)Wasting.

Depends on the carb. If it has a fuel cutoff solenoid, you will not be wasting the fuel.

Yes not recomended with wore out engine mounts. can cause bad results. The torque loading shouldnt be too much if done in a correct gear for speed you are traveling though. I kick over in 4th mostly again depends upon speed and I have not had much probblems. you may have things to fix if it is hard starting and bucks when engaged.
Something else Most dont conscider is compression ratio high compression engines bump harder. And if your using the key it is possible it restarts in clear flood mode thinking it has stumbled or stalled previously. due to ignition flash times. try counting to 3 from key off b4 returning to run position. "unless steering lock is an issue". Then I dont recomend you do it at all! install a shut off switch. Hope this answers all your concerns.

Maybe. Once the engine stops spinning though, the inlet manifold very quickly fills with air at atmospheric pressure. Every time you start the engine, it is, initially at least, in an equivalent state to wide open throttle.

It's (throttle open) easy enough to try anyway.

Fuel cutoff solenoid prevents pulling unnecessary fuel through the lines during key-off engine revs. I don't know how old your carbureted car would have to be to lack a cutoff solenoid; I think Toyotas had it in the 70s.

But it makes a huge difference to let it run down to idle and run there for a second or two before keying off. Turning off while still at high revs pulls too much fuel through unburned, and it almost guarantees a nasty backfire at the next key-on. And if you look back through my history, you can see where a backfire blew my (admittedly cheap) muffler wide open. So I spare a few milliliters of fuel to prevent that. It's worth it.

Causing the backfire was sport in my (misspent) youth. Some of the responses of bystanders were amusing until I considered that, given returned vets and gun massacres, they could have been genuinely in fear for their lives.

In Phoenix, when the walk sign comes on at intersection, there is some clicking sound which, to me, sounds like a machine gun.

I first heard it at the VA.

Some folks believe that bump-starting an engine with carburettor is safer than doing the same in one with EFI.

With my cts-v I have do a quick up down with the clutch pedal to get the smoothest kick start. A bump start should do no wear. Your using the clutch to rotate the engine internals, normally your using the clutch to move an entire vehicle.

By "kick start" you mean starting with the vehicle still in motion after an EOC?

Si senior. I should have said bump start, the motion I use with my leg would probably look like I was kick starting something.

Kick-start in this case actually makes sense :thumbup:

BTW once I've considered to work around a boat-like supplementary pull-string starting setup for an old Pontiac Trans Sport which was having constant starter failures.

When I was in college, someone was driving an old truck through the campus and let off the gas to slow down to let people cross. When the driver got back on the gas it backfired 4 or 5 times.

Probably 10 kids dropped to the ground.

Lbar, You should be pumping gas thru that 555HP "V" like it is going out of style.
I would be! Save gas in your cav and pour thru what you saved when in the caddy.

Growing up one of my buddies had an old Volvo that would backfire every time he shut it off but not for about 10 seconds. We would be out of the car and walking away watching the poor sap that happened to be walking past his heap when she blew.

Back to the OP,
Get smooth on the bump starts and even the tired motor mounts will likely hold up. One thought on clutch wear with bump starting, people who get realy high gas mileage out of their cars are easy on clutches because they never rev em up to take off or between gears. We stay out of the throttle so the clutch sees much less wear than the average stick shift driver.

Hi,
Any updates from the long term "eoc-ers"
in regards of clutch wear or battery degradation?

Starting a warm engine takes ~0.03Ah. That's why there's no noticeable clutch or battery wear.

Any additional wear on the battery is from running the accessories with the engine off. A small solar panel ~10w mounted outside the car or 20w inside, will more than offset that. Fully charged battery every time you get in :thumbup:

My 1998 Civic has 270,000 miles on the original clutch. For the last 8 years and 100,000 miles it has been EOC and clutch started dozens of times per day. Still going great.

Pulse Width Modulation of the injectors is a better way to do it..... the electrical motor force spins the engine when the injectors are off so you dont engine brake