I usually drive my RX-8 every day, but I've noticed with both of the 8s I've owned that whenever I went 1 or 2 days without turning on the car, the next time I started it, the whining noises from the rotors sounded different from how they usually sound when the car's only been off over for a few hours over night. (In other words, over 24 hours vs 8-10 hours). I'm talking about the sounds you hear as the car is warming itself up right after you turn the ignition. They sound a little quiet and different when the car's been off for a while.

What's the reasoning for this?

 

So what you're referring to is the sound of the car idling immediately after starting the engine? I doubt it has anything to do with the engine rotors. More likely it is related to the input shaft in the transmission which turns when in neutral. Here's my guess.

When the car has been sitting for 24 hours, the oil in the transmissionis is cold and, therefore, "thicker". The input shaft bearings will have a bit of play (i.e., looseness) in them by design and the thicker oil will take up some of that play cushioning the movement of the "loose" parts and dampening the sound of the turning shaft. When the oil is warm it is "thinner", and it, therefore, doesn't cushion the parts as much resulting in the familiar whining sound we all hear when our cars idle.

 

I think the oil would have cooled to is maximum "coldness" within 8 - 10 hours.

 

 

My guess is the oil has more completely drained to the bottom of the oil pans after 24 hours instead of 8-10 hours. It takes a bit for the oil to pick-up from the bottom of the pan and be circulated up and over the gearing to coat them. Once the engine is turned off, the oil starts to run back down to the bottom of the pan; the longer the car sits turned off, the more of that thick oil drips down and off the gears.

This is why it's a good idea if your car has sat for more than 24 hours to simply let it idle for a few minutes after you've started it so that the oil can coat everything properly; do NOT blip the throttle or run the revs up right away.

 

The longer my car has been off, the better it sounds when I start it. I always find that I miss the sweet sound of the rotary and the longer I'm without it, the more musical it sounds when I hear it again.

 

both my cars sometimes sound inconsistent when started up under different weather/ driving conditions. my understanding is that when the engine initially starts up the computer will attempt to tune everything. so, starting your car cold on a hot summer day might sound slightly different than in icey-snow conditions in mid-winter. perfectly normal. i don't think it's anything unique w/ the rotary engine, per say.

i think u might be just a bit over-sensitive about this... i suggest taking the stethoscope off the hood of the car and taking it for a 9000rpm spin on the open road with all the windows open. and u'll feel better...

breathe man... breathe...

 

I've found that it's more weather temperature dependant than time dependant, whether you get that cold start rumbling sound or whether you get that normal purring sound. If I leave my car parked for about 3-4 hours and the weather drops to about 65 degrees F, it'll do a full cold start at ~1.5k RPMs...after a certain point the engine makes a certain noticeable noise where it sort of just turns over, and the engine settles into the usual purring sound.

I prefer the dead cold start myself by far, that's when the car starts up the easiest. Just a second or two fires it up instantly.