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Old 07-02-2008, 04:29 PM   #1
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New guy from Nova Scotia (Canada)

Hey,
I've been lurking on here for a couple days and I figure I should post up and say Hi.

I've got a Jeep TJ and my wife has an automatic impreza so we're going thru some gas, lol. I saw a spot on TV about hypermilers and I thought why the heck not. I improved my mileage from around 16 to 18mpg on my first half tank by just not getting up to speed as quick, driving slower on the highway and slowing down earlier.

I figure the first order of business is to get a scan gauge and figure out how both the vehicles work best. what's next?

The jeep is lifted and modded up for offroading and that's not going to change, but I wonder if it's worth my time shutting the engine off when I'm coasting to slow down? EOC, right? Jumpstarting is a little obvious as the rear tires chirp like a jumbo jet landing. Is there a trick I'm missing?

Is it worth it to put the automatic (subaru) in neutral while coasting? Is the computer system going to go crazy after a while from not knowing what's going on? I'll be honest, I haven't checked the subaru manual to see if they say it's okay or not.

Anyway, hopefully someone can answer my questions. If not I'll post up in the appropriate sections like I probably should be doing

Thanks all,

Ken
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Old 07-02-2008, 04:40 PM   #2
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Welcome.

I think you mean "bump starting", "roll starting", or "kick starting" when you say "jump starting" above; jump starting is when you use jumper cables because your battery is dead. You don't have to completely dump the clutch, just get barely into the friction point in your highest gear and then shove the clutch right back to the floor. It probably will never be as smooth for you as it is in a stock little economy car, but you should be able to do it without chirping the tires!

Here's a great instruction on it...
Quote:
Originally Posted by PaleMelanesian View Post
If your bump-starting is harsh you need to refine your technique. I can do it smoothly enough that my passengers don't even notice. You want to do a 2-step process:

Clutch in. Choose highest gear. Quick pulse up-down on the clutch - just enough to get the engine turned over. It'll catch without much strain at all.

Then, choose the right gear, rev-match and let off the clutch more gently.
As for the automatic, it won't make the computer go crazy, and it has improved my MPG in my 2002 GMC Sierra. However, do NOT shut off the engine unless the manual says it's okay to tow (generally behind an RV) with all four wheels down, as most automatic transmissions depend on the input shaft to operate their oil pump. Some people think that neutral coasting an automatic will somehow destroy the transmission. Nobody can describe a reason why. I've been doing it occasionally for years, and have been doing it a lot for a few months now. I do not have enough experience to say for sure it's safe, but I have to believe there would be a lockout like there is for R and P if it was going to break stuff...and having a pretty decent understanding of how automatic transmissions work I can't say there's any reason why it should cause a problem.
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Old 07-02-2008, 04:58 PM   #3
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Oops; yeah I wasn't trying to jump start it while I was coasting with the engine off, where would I get the other hook up from, lol.

I'll give the clutch pump a shot.

I hear ya on the speculation about destroying the auto. It makes no sense that it would be bad from how I understand it works; but yet I hear all these "stories". Ah well; it's got warranty worst case. I will definitely not turn off the auto... I may call bump starting jump starting, but I know better than that

I appreciate the speedy response. I almost want to go try out the bumpstarting trick right now, but then I wouldn't be saving any gas at all.

Thanks again
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Old 07-02-2008, 05:20 PM   #4
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LOL, yeah, it's hard sometimes when I'm excited about a strategy I want to try or something, and I want to go for a drive just to test but it would waste gas since I don't need to go anywhere.

What stories have you heard? I haven't even heard any anecdotes about neutral coasting causing problems.

I do recommend vaguely rev-matching when you go N->D. In my GMC it takes a second to engage, so I shift, then step on the gas a little as it's engaging, and it rev-matches nicely.
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Old 07-02-2008, 05:39 PM   #5
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Welcome MFR! I'm a fellow Nova Scotian as well!
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Old 07-03-2008, 06:20 PM   #6
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All right! Another scotian hypermiler (well, not yet for me, but I'm trying)



It was something about not being able to rev match and prematurely wearing out the clutch packs in the auto? The Subaru seems to rev match for you; if you even touch the gas it feels like it's too much.

I tried the quick clutch pump in 5th at like 20mph and I still got a tiny wheel chirp. I might be able to refine it a bit, but definitely way better than keeping the clutch engaged. I'm gonna keep a spare rear driveshaft on me from here on out just in case I blow up a U-joint, lol.

I bought a Scan Guage II today. Awesome!
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Old 07-04-2008, 06:31 AM   #7
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I have no difficulty rev-matching my GMC, but that certainly could differ from one automatic vehicle to another.

You're letting the clutch up too far. I go as far as I would when I'm about to launch from a red light -- enough to hold the car in place on a slight hill, but not enough to accelerate it. That's about the point where it's enough to bump start. It doesn't have to rev the engine up to 1500 rpm, a good smooth bump start seems to force the engine up to 500rpm before it catches and fires up to idle, and I think it's even caught from less a few times.
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