To bump or key start?
 

I've been doing some engine off coasting lately and i was thinking if it's better to just start the car using the starter(key) when the light turns green (and i'm at the dead stop) or bump start it at about 20mph before i get to that red light.

I decided that idling for that 5-10 seconds (after the bump start) coming to a full stop, then another 5-15 seconds at the light before it turns green is not worth wasting fuel.

But i figured it will cost me about $100 to replace a starter, and assuming it will give me about 7000 starts, that's about $0.014 per start. Idling for about 30 seconds costs me about $0.012 so it's about the same if i'm sitting at the light for 30 seconds. if the light turn green just before i get to a stop i should have just bump started it.

Does this sound right?

You can wear your clutch or wear your starter and battery. I just coast in neutral and time the light best I can if traffic allows.

If I suspect a fairly short wait, I will bump start. If I suspect a longer one, I will roll up with the engine off, then use the starter.

A smoothly done bump start should cause negligible clutch wear. I usually do it in 5th gear at 10-15 mph. Just pop the clutch smoothly, then immediately disengage it as 10 mph is way down in the lug zone in 5th gear.

I agree with all of this. I keep the engine off at lights where I expect a 30 second sit. But once waiting, I consider 20 seconds or more good enough.

The debate on clutch wear has been discussed in previous threads and the common belief (on this forum) is that clutch starting is safe for the transmission/clutch as long as it is done smoothly. I will admit that there are times where I don't clutch start as smoothly as I should but, as with many things involving cars, you should be able to intuit via the sound and feel of the clutch start as to whether it's doing your car harm.

As far as coasting to a red light, waiting for it to turn green, and then starting your engine from that point - I personally would argue that it doesn't sound like a good idea.

There are several things regarding what you said I disagree with:

This will cause a delay with the people behind you, which could be argued as a safety issue. And then, let's say your starter dies at the red light. Now that's a safety issue.

Plus the labor invested, plus you being stranded without a working car, possibly missing work, etc. Also, it's debatable as to whether you're just wearing the starter. Someone above posted that it might wear the battery as well. Alternator charges battery... etc.

Keyword: assuming :)

Anyways, I know it looks like I shredded your logic apart, but really it's up for debate. This is only my opinion. There are no ten commandments of hypermiling. (except for these :) ).

Anyways, since you said that you're basically breaking even, why bother risking it? We're talking about potentially putting wear on 1 item (the clutch), versus potentially putting wear on quite a few items (battery, alternator, starter).

Anyone else have thoughts on this? I was actually surprised when I opened this post and I saw people condoning this practice but hey, I'm just a lurker (for now :) ).

When I'm approaching a red I'll bump if I know it's about to change- usually only if the left turners are already moving. Otherwise, I've got time. When I'm first at the light my "crank & go" time is always competitive with the guy in the other lane's "notice the light has changed and move foot to the gas" time. Two weeks ago someone got moving before me, but it doesn't happen often.

Keep in mind, I'm not doing stop light drag racing, I'm just trying to react quickly and get the car moving in around the same time other drivers expect someone to move in. If I'm several spots back, I just crank it when I see brake lights start shutting off.

If I'm at a red light with the engine off, I'll be in 1st gear with the clutch depressed and my hand on the key. There isn't much delay. And I watch the lights on the other street if I can see them.

I bump start as much as I can, but I won't sit idling at a light.

Maybe going key-off at a red light is more common than I originally presumed.

I still can't say I'm convinced it's a good idea though.

I'm confused here. Are you saying that you bump start 5-10 seconds BEFORE coming to a complete stop? As in coasting for 5-10 seconds before a stop but after a bump start?

Because my car take a few seconds to start with the key;
If I'm EOCing up to a red light with two or more cars in front of me, I leave the engine off while waiting, then key start.
If I'm the first in line, I'll bump start it shortly before the line and wait with the engine ticking over.

What they said.