Coasting in gear question

[HannahWCU]

Originally Posted by larrybuck

I couldn't help but notice your "handle!" Does that mean you are, or were a student at WCU?

Yes it does! Met my wife there too. Also, I didn't think of the weather conditions changing that much. I looked on the maps and it looks like that grade goes from 2800' at the peak to 1400' at the base. That is quite a difference. For the record, I calculate the grade to be an average of 5.3%.

Originally Posted by Joenavy85

You should be able to feel when the injectors shut off(I can feel it very well on my girlfriends Focus).

I can usually feel when it does, at least I think it does.

Originally Posted by SentraSE-R

Are you sure your Neon has DFCO? My wife's 2006 Elantra doesn't.

Good question, I assumed it did since I "think" I can feel them cut off, how would I check for sure?

Also, going home yesterday I checked the LOOP on a couple of the short hills I descend on my daily commute. When I "feel" the car go into DFCO the readout will go to 9999MPG and LOOP goes from "closed" to "open". So I am assuming that the scangauge is detecting it.

[SentraSE-R]

Going into open loop means you have DFCO.

[Joenavy85]

Originally Posted by larrybuck

I've been up and down the grades of I-80 across Wyo. many, many times.

I'll be going throught there next weekend on my way out to California. I'll be stopping in Rock Springs for a night then driving through Utah and Nevada the following day, all the way to Sac Town.

[HannahWCU]

Filled up yesterday. This was a tank to Asheville and up (and down) the Old Fort Grade. Again the scangauge was off, it was reporting 40.6 and my calculations was 38.25, an almost 6% difference. Normally I don't see much over 0.5 MPG (+/- 1-2%) difference between the scangauge and actual.

I don't think anything is wrong with the scangauge, I just think the car is actually burning fuel when it is reporting that it isn't. I was just wanting to know if anyone else had ran into a similar issue. Thanks to everyone for the read and the advice.

[SentraSE-R]

I see that much variation all the time, due, I think, to differences in tank fill levels. I try to fill at low speed until the automatic shut-off kicks in, and repeat three times. Even then, I can occasionally add an extra 0.5 - 1.0 gallon after the first click.

[HannahWCU]

Originally Posted by SentraSE-R

I see that much variation all the time, due, I think, to differences in tank fill levels. I try to fill at low speed until the automatic shut-off kicks in, and repeat three times. Even then, I can occasionally add an extra 0.5 - 1.0 gallon after the first click.

Yep, I agree with that. But that should show up in the next fill. If I overfilled this tank (resulting in an abnormally low MPG), then the next should show as an abnormally high MPG fill. That did not happen last trip to Asheville (7-6 fill). However, I did do that that on the 6-1 fill, so I averaged it with the 6-12 fills to eliminate these as abnormally high and low fills from my statistics. I also fill at the same gas station every time (with a few exceptions that i have noted in my fuel logs) to help minimize this issue.



Not saying that isn't the problem, but it is strange that it has happened on those two trips. That being said, since 4-3-2011 I am fairly consistent with my MPG. The one notable exception on 5-15 was due to a lot of city driving (~40%)

[euromodder]

Originally Posted by HannahWCU

I don't think anything is wrong with the scangauge, I just think the car is actually burning fuel when it is reporting that it isn't.

For the record, I calculate the grade to be an average of 5.3%.

My car - likely heavier than yours - needs around 5% to sustain about 60 mph while coasting (engine on).

If you keep it in gear, I'd expect it to add fuel on the lesser grades and engine brake on the steeper ones.

Any chance you can run downhill in neutral without reaching too high a speed ?
Maybe by starting the rollercoaster ride slower.

[AeroModder]

I ran into this problem with my scangauge. The DFCO calculation on the SG uses throttle position. My readings were funky while I was trying to get DFCO, so I just turned that feature off. Now my SG is spot on.

[basjoos]

Originally Posted by HannahWCU

Sorry for the long post.

I do fairly well hypermiling, but I have a question about coasting. My 2004 Neon is a 5-spd and depending on the steepness of the hill I am descending, I will either take the transmission out of gear (if I don't need the engine breaking) or leave it in gear so that the fuel will cut off and increase my mileage.

My concern is that I was recently traveling from Asheville, NC to Hickory on I-40. Anyone who has traveled that road knows how long and steep I-40 gets on Old Fort. It is about a 4-5% grade for about 5 miles. I left my Neon in gear and the fuel cut out (I monitor this on my scangauge). For the first time I had the Water Temp on the scangauge because of the heat outside and I noticed something strange. The water temperature of the engine dropped to 196 after about 1/2 mile and stayed there (didn't go any lower).

Now I would think that if the fuel was shut off for the 5 minutes it takes to coast to the bottom that the engine would continue to cool the whole way to the bottom. I am traveling between 55-70 MPH, so air is flowing over the radiator (and the engine) the whole time.

I also would think that the thermostat is still open at this temperature because during the winter my car runs 190-192 and when coasting (engine on) I have seen as low as 185.

The reason I am wondering about this is when I checked my mileage for the tank coming from Asheville there was a BIG difference between what the scangauge read and what the actual calculated mileage was (~10%). I have to wonder if the engine is actually burning fuel but the scangauge doesn't see it.

Any thoughts?

The reason your coolant water temperature didn't drop below 196 while engine braking down the Old Fort grade was because you were continually putting energy into the engine. Just as using the friction brakes heats up your brake pads, using engine braking heats up the engine via friction and compressing air in the cylinders. All of that external rotational energy entering the engine has to go somewhere and it eventually gets converted into heat.

[HannahWCU]

Originally Posted by euromodder

Any chance you can run downhill in neutral without reaching too high a speed ?
Maybe by starting the rollercoaster ride slower.

I start the decent at the top at 55mph in gear, the grade is steep enough that, even with engine braking, I have to apply the brakes to slow the car from 70 to 55 at least 3 times before I get to the bottom. In neutral, I would almost have to drag the brakes the whole way.

Originally Posted by basjoos

The reason your coolant water temperature didn't drop below 196 while engine braking down the Old Fort grade was because you were continually putting energy into the engine. Just as using the friction brakes heats up your brake pads, using engine braking heats up the engine via friction and compressing air in the cylinders. All of that external rotational energy entering the engine has to go somewhere and it eventually gets converted into heat.

I guess that makes sense. I just didn't think the internal friction would generate that much heat.

Originally Posted by AeroModder

I ran into this problem with my scangauge. The DFCO calculation on the SG uses throttle position. My readings were funky while I was trying to get DFCO, so I just turned that feature off. Now my SG is spot on.

That could be it. I try to do as much DFCO as possible and the scangauge and the actual are always pretty close. Maybe next time I make the trip I will cut DFCO on the scangauge off and see what the results are.

Thanks for all the help and suggestions! Love the forum!