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Discussion Starter #1
Per the manual, to check the oil level in the 2.5L engine you want to bring the car up to operating temperature. Then after it has sat for at least 5 minutes, check it. Does your reading change whether its hold or cold? Some still check the level after the car has sat overnight.
 

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I have never had a vehicle where the oil level cold is MORE than the oil level hot. I typically find the change / increase - cold-to-hot - is pretty moderate. I typically check cold because with hot oil, particularly with freshly changed (i.e. clean) oil, I find it quite hard to check oil on my Skyactiv-G 2.5. It is somehow due to the design of the dipstick system... It does not allow the freshly-wiped and reinserted dipstick to accurately maintain the "interface" as it's pulled-out of the tube for checking. Not so when left overnight. Oh, BTW, I typically run my oil level at 3/8's to 1/2 way up the range, cold. I don't want to unduly "challenge" the two crankshaft oil seals. This consideration is probably overkill, I would concede.

Having said all of the above, I am thankful to actually HAVE a dipstick (unlike recent BMW's, etc.)
 

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Great points. From what I have read, the 2.5L takes 5-5.4qts to reach the top hole on the dipstick. I have a feeling the 4.8qts they list in the manual is to account for what the oil is hot. Due to thermal expansion, checking the oil 5-10 minutes after the engine has reached operating temperature it reads slightly higher. This has been the case so far with my car. When cold, it's a tad below full. Checking it per how they say in the manual it is exactly on the full mark.
 

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Thermal Expansion in oil will only make about a 2-3mm difference on the dip stick as the Volumetric Coefficient of Expansion of Motor oil is around 0.00070 Per 1 Degree Celsius.

I would not worry to much if your filling to the full line and checking Cold or Hot... the 2.5L in the Mazda 3 you can overfill by quite a bit before it will cause issues.. Most manufacturers put in a safety margin when it comes to the indication marks on a dipstick..

I have a 2019 but have not had the oil pain off.. but its the same engine as the 2015 I had... with the oil pain off you could see that you would have to go pass the full mark around 2cm or just under an inch before you would start getting trouble with aeration of the oil.

In the end I'm just saying if its in between the lines hot or cold after you let the oil settle you will not have an issue!



 
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