The dirty cost of one man's hypermiling?

[SentraSE-R]

Thanks, Mech. I burned up my wife's car's engine. Started down the highway in 20 degree F weather, and noticed no cabin heat. By the time my addled brain figured out the problem, the engine was fried.

I retired my old fuel log and set up a new one. Mean Green Toaster Machine averaged 49.4 mpg over 30,375 miles, 176% of EPA. Clean Green Toaster Machine is averaging 45.8 mpg over 2235 miles, 164% of EPA. Unfortunately, the city tanks are ~40 mpg instead of 55 mpg, while the highway tanks are about the same.

[California98Civic]

Originally Posted by SentraSE-R

I'll find out tomorrow. I suspect there will be no difference, since my 25-40 mph 4th gear P:G ratio is ~ 1:3, and my 18-32 mph 3rd gear P:G ratio is 1:5. My guess is the cat will cool below its light-up temperature with 3-5 times to cool after every pulse.

The DFCO test will be interesting. It would also be great if you still had your grill blocks in place, since they would help protect the cat from cooling. If today's test suggests that the most rigorous EOC P&G will keep the CAT from lighting over short journeys, where would the balance be? Put another way, the test could be to see how much EOC P&G you can "get away with" and still keep the CAT lit.

[SentraSE-R]

CACivic, you're right. The unlit cat temperatures are just begging me to reinstall my grill blocks, and if there's an improvement, to reinstall my WAI. I don't know if there's any relationship between air intake temperature and cat temperature, but the answer's only a test away.

And, in the spirit of Mech's "never surrender" advice, it's time to re-examine cat wraps and insulators. I think most of us recognize the elephant, Don Quixote & Sancho Panza aside. Now we have to deal with it.

[Arragonis]

How about engine on coasting instead, would that be OK ? I tap this as I do this a lot and I have a Toyota with a cat just after the exhaust manifold.

[cfg83]

Arragonis -

Originally Posted by Arragonis

How about engine on coasting instead, would that be OK ? I tap this as I do this a lot and I have a Toyota with a cat just after the exhaust manifold.

I think that is already the fallback strategy. Happiness is a warm cat :



CarloSW2

[SentraSE-R]

Starting with a cold engine (~45F), cat sensor 1 reached 550 degrees F in 3 blocks. Cat sensor 2 didn't reach 550F until 7 blocks, at which time sensor 1 was at 800F.

The grill blocks made no difference. EOC after a pulse, and the cat failed to light on the next pulse, grill block or no grill block. Following photo shows cat temp display at the end of yesterday's 10.4 mile P&G drive.


My downhill wasn't long enough. I accelerated to 60 mph at the top of a hill, and went into DFCO at 1100F cat temp. Cat temp rose to 1300F before dropping to 750F at the bottom of the hill, 1.2 miles later. So, unless you're DFCOing 1.5-2 minutes/miles, you can assume your cat stays lit.

Typical cat temps when driving under load.

[roflwaffle]

The cat may stay lit even if there's a longer DFCO if the ECU sends a little extra fuel it's way when it sees it cool off.

[California98Civic]

Originally Posted by cfg83

Happiness is a warm cat

That's great, CarloSW2.

I wish I had the readouts on my UG that you have, Sentra. My car is too old, apparently. This test leaves questions only suggestively answered. I would think that warming the car up to running temps during the first miles of this 10.4 mile trip would mean you could then hypermile the remaining 7 or 8 miles, with the EOC pulses not needing to heat-up the CAT but rather only maintain its heat. If a mile and a half of DFCO does not cool the CAT enough to make it function poorly, then it stands to reason that EOC glides with short pulses could keep the CAT lit longer too.

[Superturnier]

I think the flow through the cat is quite small under DFCO, since the throttle is closed.

[California98Civic]

Originally Posted by Superturnier

I think the flow through the cat is quite small under DFCO, since the throttle is closed.

And the flow through the CAT during EOC would be nil since the engine is off. Therefore much of the CAT's cooling that Sentra has observed must be from external cool air, not air flowing through the CAT. Strategies for insulation would slow that cooling rate.