zzum-zum

At the end of May I drove from VA to South Carolina to see my Dad. The trip is a little over 500mi. On the way down I got my usual 19 mpg highway. I started the car to head back to VA on Saturday morning. All of the display lights and the radio were dead. I turned off and restarted the car and everything worked, but the engine light was on. I went ahead and drove back home, the car ran fine - and was getting 23.5mpg.
I was going to call the dealer on Monday, but when I started the car Sunday the light was off and everything seemed fine.
Last week the same thing happened when I started the car to go to work. I went to the dealer that afternoon. They diagnosed the problem as the alternator going bad and replaced it (under warrenty - I have 39000mi on the car).
Any ideas why the gas mileage would have increased with this problem? It makes me wonder if they diagnosed the problem correctly.

alnielsen

iTrader: (4)

Bad alternator not charging the battery. Causing less drag on the engine?

Sigma

Though I don't know about the RX-8, it's common in cars for engine light illumination to adjust fuel delivery and timing with the engine which can positively affect mileage. The downside is that it also affects performance.

KYLiquid

i would have to agree with this for the most part. could cause the car to run LESS timing....although you would think the RX8 in safe mode would just be dumping buckets of fuel into the engine, not less (more mpg) but whatever.

Did you notice any performance losses with the light on.

also, maby you car really wants to get the good miliage and the bad alternator was causeing more drag giving you worse miliage

zoom44

heheeehe we dont HAVE an altenator

Bigdog6060

really?

zoom44

its a generator

rx8cited

They screwed up the 2004 Owner's Manual and called it an alternator ........... I want a new corrected manaul :D.

missinmahseven

o.O I thought generators went to the Big Junkyard in the Sky in the late 60's, in lieu of a more efficient and smaller alternator with a rectifier to make the DC...

I swear the alternator on the Renesis is the same Mitsubishi unit Mazda has used since Nixon was president... at least it looks the same..

Okkay, I just looked it up -- mazda calls it a generator, but in reality it is an alternator, producing AC instead of DC... tehre's a rectifier after it. If you'd be making DC, like a generator does, there'd be no need to rectify it into DC..

It's an alternator.

zoom44

what is it called again? by mazda?

missinmahseven

Hai, hai, they call it a generator. I'm surprised they didn't call it a dynamo or some equally quaint name.

So what is it? Forget about what Mazda named it. What does it produce? AC or DC?

It produces AC.

zoom44

i dont care the tech was wrong- if he tried to order a rx8 altenator from his parts guy he would get the same answer- "there isnt one, but how about a generator?" hehehehehehe

zzum-zum

The service rep definitely said it was the "alternator". Probably because they don't want to get into alternator/generator arguments. In any case, I noticed no loss of performance, but i really don't push the car anyway. I wouldn't mind getting 24mpg all the time.

rx8cited

So why do we have a generator instead of an alternator? Is this a Mazda-wide thing or a rotary thing?