Just had my engine replaced a week ago under the Mazda Warranty (had only 35k miles on it and it threw a CEL and dealer determined bad compression), and when I got my car back last friday, I started to notice that every time I came to a stop or parked, or reversed and then stopped, I get a really weird sloshing sound. I've checked the inside of my car for bottles, etc, and took out the extra quart of oil I keep in the trunk, but its still doing this (I figured it was too loud to be that, but I just wanted to make sure I wasn't being retarded). It sounds like it's coming from the gas tank...I already made the appointment to bring it down to the dealership saturday, but if I can avoid doing that, it would be awesome (it's a good 30miles away).

Any ideas?

On another note, I've already gone through a quarter of a tank and only made it 50 some miles...before the CEL threw on the previous engine, I would usually get around 70-80 miles through a quarter tank...typical new engine break-in or dealership fail?

 

Sloshing sound like walking through puddles? I can't imagine the noise you are trying to identify.

 

Sloshing sound like if you had a 1/2 full gallon milk jug and shook it slowly back and forth is the best way I can describe it.

 

Could be gas shifting around? If I remember correctly, we have a saddle style tank so it could just be that.

Mileage seems to vary a lot from car to car (engine to engine). I doubt there's anything dealership did that would have affected your mileage. Has you driving style been the same? How about conditions (city vs highway)?

 

Also "quarter of a tank" is really not a good indicator of how many miles you are actually getting, your reading could be off, or your fill up/top off wasn't as much as last time, etc etc.

 

Yea, I'm pretty sure our tank is saddle style too. What worries me is I didn't used to hear this sound before...I just wanted to see if anyone else hears this sound in their rx8 too (may require turning music off). I might delay taking it to the dealership so I can get it down to a quarter tank left and see if it still makes this sound...I still don't think it's normal though...at least nothings leaking as far as I can tell.

I understand that quarter of a tank is not a good indicator...so I'll wait and see.

 

I'd honestly say give it a couple tanks and see how your mileage is looking. If you're getting between 17-20, that's pretty average and there's probably not much the dealer would be able to do. If you're getting lower than that, then maybe something is wrong. Like I said, it varies from car to car (engine to engine)... some people get like 14 mpg, but I can only assume something is wrong with their car lol.

As far as the sloshing goes, when I had my 8 I would occasionally hear something that might be similar to what you're describing. It always came from the back and was kind of like a sloshing sound... a bit like a trickle (like overflowing from one thing into another). I always assumed it was the gas shifting around.

How often/consistently does it happen? If someone were to ask you to make it happen, could you? Or is it kind of random?

 

Water in the door panel?

 

Yea, for the sloshing, it happens consistently everytime I come to a stop. If someone asked me to reproduce it, I could do it easily. I'm hoping when I pull into the dealership bay on Saturday morning, it'll do it when I stop and they'll be like wtf, it should not be making that sound, and have a quick fix. With my luck though, they'll need to order the part, etc...

I doubt it's water in the doorpanel...I would be able to hear that if I open and shut the doors...

 

Well, prognosis when I brought it in on Saturday was that it was definitely coming from the gas tank and that it could be broken baffles. Apparently the service department contacted the engineers at Mazda and tested the 8s they have in stock to see if it made the same noise...and supposedly they do... So I guess I have to live with it... Anyone getting the same sound on their 8s? If so...I feel like Mazda engineers should fix this with a TSB...

 

I have never heard that in my car before. Although, when you put a full straight exhaust on your car...It's hard to hear much of anything.

 

Are you sure it doesn't sound like broken glass? Could be the catalytic converter? I had similar recently and that's what it turned out to be.

 

I get the exact same sound as the OP. I always figured it was the gas sloshing in the tank. It surprised me at first, but it doesn't seem any worse than a minor annoyance.

 

Take the fish tank out of the back seat .

 

You might have air in the heater core...it can make a funny noise sometimes...it should go away after it bleeds out.

As for the gas tank sloshing....I have never heard it on mine...but I am half deaf...and my exhaust is far from quiet

 

I am in a similar situation as you engine wise and am getting this same noise too when I vary the revs; my noise is coming from behind the dash. It is most likely air in the cooling system, fingers crossed, so I'm going to bleed it as soon as the car cools off.

This might be your problem too. Worth a look.