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Old 01-30-2012, 01:53 PM   #1 (permalink)
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The dirty cost of one man's hypermiling?

My car failed CA emissions testing recently, and I'm confident my hypermiling had a direct relationship to the problem. When I took it in for the test, I hadn't driven the car in a month, except for a brief drive up the freeway to warm the engine up before the test.


The failure was because some of the drive cycle monitor readiness flags hadn't been set since I cleared the check engine light/malfunction indicator light in October. Since then, I'd driven 800 miles, but the catalytic converter driving cycle is 15 minutes at speeds between 60-100 kph, and I hadn't done that in 4 months.

The next day, I warmed the car up, driving it enough to add 100 miles since the test failure. The car passed smog testing. Examination of the retest shows cleaner emissions after driving the car a distance at speed. Low speed HC results had been 62, only 2 below the maximum allowable level, but dropped to 39 on the retest. Inactivity or the normal way I drive may be raising my emissions, as my HC levels are 3-15X more than average, CO levels are 1-6X the average, and NO levels are 4-7X more than average.


I drove the car 900 miles RT to/from SoCal last week, and the cat stayed lit, between 1101-1185 degrees F. When I do my normal low speed P&G, cat temps are 285-550 degrees F, too low to light the cat.

I know today's cars burn much cleaner than older cars, but I lived through pre-Clean Air Act smog conditions, and I don't like the idea of my car dumping out 3-15X the average air pollution when it's driven normally. I can only guess how bad it is with an unlit cat.

So, P&Gers like me are gross polluters. Lean burn Hondas (including some Insight Is are polluters. The pre-OBDII cars are polluters.

I'm disillusioned by the growing realization that pollution is the hypermiling community's dirt we're sweeping under the carpet.

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Old 01-30-2012, 02:29 PM   #2 (permalink)
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I take issue with the thread title. You point a finger at all of hypermiling in general for the potentially negative effects of one very specific tactic. It's unnecessarily inflammatory.
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Old 01-30-2012, 02:33 PM   #3 (permalink)
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How are you measuring CAT temperatures? Do you have any data previous to P&Ging that supports that it is the problem (though it does sound logical)?

I definitely agree the title is a bit dramatic when its one hypermiling technique that is the possible issue here.
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Old 01-30-2012, 02:35 PM   #4 (permalink)
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I don't think its one very specific tactic... any time the engine spends off is going to let the cat cool down, decreasing its cleanliness. Turning the engine off at lights, coasting, P&G, etc.

I wonder... do modern hybrids have small cats/pre-cats designed to cope with this where non-hybrid vehicles do not? Do they have a special heat wrap or thermal insulation to retain heat between startups that may be minutes apart?
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Old 01-30-2012, 02:39 PM   #5 (permalink)
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Hi Darrell,
Very interesting observation. It further points out the damaging effects of short trips in which the vehicle doesn't get hot enough to operate at its maximum efficiency. Still you have to look at the total pollution that one generates vs the mileage covered before you throw the baby out with the bath water. I know you do a lot of EOCing , maybe you could switch to engine on coasting to maintain higher cat temperatures.
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Old 01-30-2012, 02:39 PM   #6 (permalink)
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Newer cars in general have had their cats moved up closer to the engine for a while now. I assume it is to get them to lite up quicker and retain more heat. Where as my 97 Paseo has the cat behind the engine bay, my 03 Matrix had the cat right off the exhaust manifold.

When you start a Prius up it runs for a set amount of time specifically to lite the cat. However, the new plugin Prius does not do this. If you need the power it'll kick the engine on for a few seconds and then shut off once the load is lower again. There is no insulation that I know of.
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Old 01-30-2012, 02:43 PM   #7 (permalink)
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Anytime a car is driven in a way that the automotive engineers didn't foresee or is way out of the norm it has the potential to knock the emissions controls out of whack. This includes feather footing it as well.
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Old 01-30-2012, 03:10 PM   #8 (permalink)
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Daox, my UG shows cat temps.

Darin, while my pollution example is P&G, there are other hypermiling pollution examples I included in this topic. The lean burn CR-Xes, Civic HF/VXes, Insight I with their high NO emissions, so sought after by some hypermilers. The hypermilers who purposely choose pre-OBDII cars so they can swap older, higher-polluting engines in and strip heavy OBDII junk out.
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Old 01-30-2012, 03:19 PM   #9 (permalink)
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I wonder how that is calculated since there are no temp sensors in (most) exhausts?
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Old 01-30-2012, 03:43 PM   #10 (permalink)
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If your car fails emissions testing because too much driving in lower rpms has partially clogged the cat, you only need to drive it for a mile or two in very high revvs and it will pass the testing.
But you are correct about emissions, coasting in neutral is a lot less polluting and so are OBD-II cars. And I`m not arguing here, the numbers are on the side of newer cars and that`s a fact.

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