Quote:
Originally Posted by deathtrain
ok confused a little. Bruce what you did (if i read this right) was to add a battery and you got a plus in MPG because the alternator was not working as hard.
Or adding the battery is just allowing you to EOC longer than you where. And thats how you got the gain in MPG?
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The second one is what's happening. The two batteries wired in parallel - just like when jump starting - have approximately double the capacity of the single battery. So with no support from the alternator when coasting, they last longer before voltage drops to "too low for comfort". Yesterday I was able to coast whenever I wanted, as long as I wanted, never needing to spin the engine to keep the battery voltage up. Voltage readout is on the dash, of course.
The alternator has to work just as hard because the car's needs for current haven't changed. Lights, fuel pump, ignition, computer, etc. etc. all the same. The batteries are just a "storage bucket" of sorts.
I have to say that not all the gain is from the increased battery system. Something has changed in the engine and/or computer that's allowing it to be in lean burn mode (an original factory feature of the Civic HX) at lower speeds for longer amount of time. This changed just over the last couple days. I don't know if some EGR piping finally got cleaned out or what. Maybe some rings got degunked and aren't sticking. Maybe the upped battery capacity has something to do with this improvement but I doubt it. In any case, I can do a much higher percentage of my commute in lean burn now, and at lower speeds. I just hope it lasts, because it's a real benefit.