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Low MPG and a little "hot-start" problem..

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Old Nov 20, 2010 | 01:53 PM
  #1  
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Low MPG and a little "hot-start" problem..

... what could it be??

After doing research around here, my best guess is low compression, but before I take it to the dealer for a test I thought I should ask you guys first.

Here's some more details about the car:
05 Shinka 6speed mt
69k miles
Plugs, wires and coils were just replaced about a month ago
Averaging 13.5mpg (my last two fill-ups were 14 and 13, 70% city driving)
The car still starts when warm.. but takes about 3-4 sec more of cranks than when cold

Any other theories or suggestions of what to do next?
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Old Nov 20, 2010 | 02:01 PM
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the mpg isn't always a great indicator as it can change quite a bit based on your driving style.
Could it be a starter issue?
still running an OEM catalytic converter?

any other symptoms?
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Old Nov 22, 2010 | 01:39 PM
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The starter and catalytic converter haven't been changed. I'm probably wrong here, but if the starter is the problem, wouldn't the hard-start happen both when the engine is cold and hot?

No other symptoms that I know of; no loss of power (though not entirely sure, as I only had the car for 2 months). Anything in particular that I should be looking out for/pay special attention to?
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Old Nov 22, 2010 | 02:07 PM
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I've discovered that the thermometer, when set to Celsius, is a good indicator of expected gas mileage. 13.5 is pretty normal for this car in this weather.
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Old Nov 23, 2010 | 10:33 AM
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The weather is getting cold where I'm at (Pittsburgh, PA), but even so I've never got 15 mpg or more even when the weather was still warm; it's been consistently 13-14.

According to fuelly.com that's way below average... but is it? If its normal then I wouldn't need to worry so much
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Old Dec 2, 2010 | 10:26 AM
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So I just got back from a compression test at a dealer, results they gave me are:

Rotor 1:
5.1
5.0
5.0

Rotor 2:
4.9
4.8
4.9

@182rpm

Running the numbers through the calculator gives me about 6.7 and 6.5 avg @250rpm, both under Mazda's min spec for rotary engines (6.9).

I got my car back and they are filing the request to Mazda NA and will call me whether I am getting a new engine or not. The only thing that worries me is that since I only got the car ~2 months ago I only have 1 oil change receipt. Hope it goes through anyways
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Old Dec 7, 2010 | 08:50 AM
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*Update* Engine's on its way! Will be here in 3-4 weeks! =D

This is good news to all trying to get engine replacements; I got it with only 1 oil change receipt.
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Old Dec 7, 2010 | 09:01 AM
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Hot start issues are more times than not directly related to poor compression. Schedule yourself an appointment at your local dealer.
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Old Dec 7, 2010 | 10:35 AM
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Originally Posted by terch1
Hot start issues are more times than not directly related to poor compression. Schedule yourself an appointment at your local dealer.
??.. I already did -- a new engine's on its way. Did my previous posts not show up?
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Old Dec 7, 2010 | 10:55 AM
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My bad! See I was right. lol.
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