Startup question as it relates to 0w20 vs 5w30

[Bojo]

Ok. I have to explain something, and ultimately I have a question at the end.

I decided, to use 5w30 INSTEAD of 0w20 for my new 2025 CX 5 Skyactive engine NON turbo. It calls for 0w20 , but due to cafe standards and many opinions, i went with 5w30 on my first oil change.


I live in Texas where its cold now but NOT brutal winters.

My reason for switching to 5w30 is because its supposedly provides slightly more wear protection overall, based on my research.Better for engine, not for cafe standards type of thing.


Having said all that, here is my question:

If it is true that 90 percent of engine wear occurs at STARTUP, and 0w20 gets to the engine QUICKER at startup, doing the math, does not this make the 0w20 a better choice then, no matter what tests show 5w30 is better overall (while driving etc)?



Make it make sense!

 

[GW.]

5W is good for -25f or so. I think you’ll be fine. 0W-30 is an option too.

 

[rstsco]

Go with a 0W-30. Best of both worlds!

 

[fantastic]

Certainly a 5w is no issue in your climate.

 

[kschachn]

It’s not true that 90 percent of wear occurs at startup. That myth just won’t die and keeps getting repeated here it seems.

The winter rating is for cranking and pumpability, not wear. In Texas the difference between an oil with a 5W rating and one with a 0W rating is utterly meaningless. It would only have meaning below about -30 or so.

Your oil will get everywhere it needs to get in the same amount of time. Another Internet myth, you’ve read a lot of them apparently.

 

[Bojo]

It’s not true that 90 percent of wear occurs at startup. That myth just won’t die and keeps getting repeated here it seems.

The winter rating is for cranking and pumpability, not wear. In Texas the difference between an oil with a 5W rating and one with a 0W rating is utterly meaningless. It would only have meaning below about -30 or so.

Your oil will get everywhere it needs to get in the same amount of time. Another Internet myth, you’ve read a lot of them apparently.

Yes I have !! Lol.. thanks, this makes sense

 

[JavierH19]

On cold start no, the 90% figure is exaggerated. On hot start with thin probably but even then not that high percentage wise. Thicker oil reduces startup wear as the residual film provides more separation and as long as it still pumps good which a 0w-30 like ESP will especially in the not awful texas winters you can switch. But if you change your mind stellar 0w-20's like Mobil 1 ESP, Pennzoil Ultra Platinum and Castrol EDGE Extended Performance are better than what the dealer would put in. And the 30 grades of those three are better still.

Here's a good thread on that, shame it got locked so soon. TWX summed it up better than I could.

T

Post in thread 'Effects of start-stop tech on bearings = more wear'

Oct 4, 2025

Engine is off, oil pressure goes to zero. Then re-start a minute later ??? It's like doing "dry starts" all the time IMO. Has to be added wear on bearings due to no oil pressure.

The increase in wear isn't due to the lack of oil pressure. There's enough oil in the bearing to provide lubrication until the bearings get oil pressure again after a second or so.

The wear is due to the fact that hot oil is too thin to provide hydrodynamic lubrication at very low rotational speed, like when the engine first starts cranking, which results in some brief metal on metal contact.

Here's...

• twX

• 
• 

 

[ripcord]

There is a big misconception about startup wear. There is increased wear at startup, but it doesn't all happen in the first second or two like most people imagine. The majority of the increased wear happens while the engine is still cold. Anti wear additives in the oil and deposited on the internal surfaces do not fully activate until those internal engine surfaces are hot. This is why one should drive gently until the engine has a chance to warm up.

For all the temperatures that you'll see in Texas, there is a negligable difference in the initial circulation times between 5w-30 and 0w-20.

 

[Urshurak776]

I also use 5W-30 in our 2024 Mazda CX-5, non-turbo and in our 2023 Mazda 3, non-turbo. Both have the same engine as yours. I live in South Carolina, so same situation as you also. It will never get cold enough here for there to be any difference between 0w-30 and 5w-30 during start-up.

Circulation time difference, measured with my okinokibafoki tool (measures out to 1 million decimal places) recorded a full circulation time difference of:

.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 seconds in favor of the 0W-30.

EDIT: Forgot a zero.

 

[Bojo]

On cold start no. On hot start with thin probably. Thicker oil reduces startup wear as the residual film provides more protection and as long as it still pumps good which a 0w-30 like ESP will especially in the not awful texas winters you can switch. But if you change your mind stellar 0w-20's like Mobil 1 ESP, Pennzoil Ultra Platinum and Castrol EDGE Extended Performance are better than what the dealer would put in. And the 30 grades of those three are better still.

Here's a good thread on that. Shame it got locked so soon.

T

Post in thread 'Effects of start-stop tech on bearings = more wear'

Oct 4, 2025

Engine is off, oil pressure goes to zero. Then re-start a minute later ??? It's like doing "dry starts" all the time IMO. Has to be added wear on bearings due to no oil pressure.

The increase in wear isn't due to the lack of oil pressure. There's enough oil in the bearing to provide lubrication until the bearings get oil pressure again after a second or so.

The wear is due to the fact that hot oil is too thin to provide hydrodynamic lubrication at very low rotational speed, like when the engine first starts cranking, which results in some brief metal on metal contact.

Here's...

• twX

• 
• 

I will definitely check this thread out thank you! (yes ive seen a number of threads that were getting really interesting then suddenly closed) Not to digress too much , but you mentioned stellar 0w20 oils, wouldnt Mazda 0w20 gf5 oil with moly classify as a stellar 0w20? Not that it matters much as Im getting mrore and more comfortable with the 5w30. but IM just curious if I ever do switch back and maybe for others that insist on staying with 0w20.. i did hear that its a standout 0w20 oil. Curious what you think about that particular oil.

I also use 5W-30 in our 2024 Mazda CX-5, non-turbo and in our 2023 Mazda 3, non-turbo. Both have the same engine as yours. I live in South Carolina, so same situation as you also. It will never get cold enough here for there to be any difference between 0w-30 and 5w-30 during start-up.

Circulation time difference, measured with my okinokibafoki tool (measures out to 1 million decimal places) recorded a full circulation time difference of:

.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 seconds in favor of the 0W-30.

EDIT: Forgot a zero.

I also use 5W-30 in our 2024 Mazda CX-5, non-turbo and in our 2023 Mazda 3, non-turbo. Both have the same engine as yours. I live in South Carolina, so same situation as you also. It will never get cold enough here for there to be any difference between 0w-30 and 5w-30 during start-up.

Circulation time difference, measured with my okinokibafoki tool (measures out to 1 million decimal places) recorded a full circulation time difference of:

.0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001 seconds in favor of the 0W-30.

EDIT: Forgot a zero.

Thats great!!! Just curious what oil you are using.. Im using Pennzoil Ultra Platinum...5w-30...

 

[Urshurak776]

I will definitely check this thread out thank you! (yes ive seen a number of threads that were getting really interesting then suddenly closed) Not to digress too much , but you mentioned stellar 0w20 oils, wouldnt Mazda 0w20 gf5 oil with moly classify as a stellar 0w20? Not that it matters much as Im getting mrore and more comfortable with the 5w30. but IM just curious if I ever do switch back and maybe for others that insist on staying with 0w20.. i did hear that its a standout 0w20 oil. Curious what you think about that particular oil.



Thats great!!! Just curious what oil you are using.. Im using Pennzoil Ultra Platinum...5w-30...

Usually use Quaker State Ultimate Protection, but snagged (4) 5QT jugs of Kirkland synthetic for like $9 each during last Costco sale. So, will use that then go back to Quaker State UP.

 

[2.7ecoboostFordBronco]

I agree with your decision to use 5W-30. As long as you are not attempting to start your vehicle below -20F there is not much downside. You might lose ~0.5 horsepower and ~0.2 mpg, differences that would only be noticeable in a test lab. In return you get better wear protection, including on cold starts, unless it’s so cold that the oil won’t pump (below -20F).

The thread below discusses research indicating that the observed elevated startup wear is most significant on cold starts and that it is related to corrosive combustion byproducts and oil film thinness, not “flow”. It seems to suggest a thicker oil may actually protect better on cold starts, as long as it is able to be pumped (you’re not starting below the minimum temperature for your oils winter grade).

Thread '75% of wear occurs at startup...'
https://bobistheoilguy.com/forums/threads/75-of-wear-occurs-at-startup.251019/

 

[JavierH19]

I will definitely check this thread out thank you! (yes ive seen a number of threads that were getting really interesting then suddenly closed) Not to digress too much , but you mentioned stellar 0w20 oils, wouldnt Mazda 0w20 gf5 oil with moly classify as a stellar 0w20? Not that it matters much as Im getting mrore and more comfortable with the 5w30. but IM just curious if I ever do switch back and maybe for others that insist on staying with 0w20.. i did hear that its a standout 0w20 oil. Curious what you think about that particular oil.



Thats great!!! Just curious what oil you are using.. Im using Pennzoil Ultra Platinum...5w-30...

It's very high moly but it's the older style of moly which had to be in really high concentrations to be very effective. On top of that I don't believe Mazda has updated their oil and it's likely still stuck in SN. I'd bet good money the three would out perform that older formulation high moly Mazda oil not just in things like oxidation resistance, lspi, soot thickening, and cleanliness but wear protection too. The newer style of moly is the trinuclear kind and believe something else as well since it's usually a mix and they are very effective in low ppm concentrations and can match the performance of the older moly in its high concentration.

 

[facility1]

why not use 0w-20 in winter months and 5w-30 in summer times, Pennzoil Ultra Platinum is a fine oil (GTL base oil) to use or AMSOIL Signature Series , good mrv and ccs test results, quick flow is what you want on start-up. and yes there is about 70% wear at cold start up.

 

[YZJB]

In Australia most Mazda dealers use 10W-30 in these engines. No need to stress about 5W-30 at all.

 

[Japanese]

Your oil will get everywhere it needs to get in the same amount of time. Another Internet myth, you’ve read a lot of them apparently.

Well, I hear louder my cam chain and VVT with 5W-30 below 20*F and that tells me it's not as fast as 0W-20.

 

[Bojo]

I agree with your decision to use 5W-30. As long as you are not attempting to start your vehicle below -20F there is not much downside. You might lose ~0.5 horsepower and ~0.2 mpg, differences that would only be noticeable in a test lab. In return you get better wear protection, including on cold starts, unless it’s so cold that the oil won’t pump (below -20F).

The thread below discusses research indicating that the observed elevated startup wear is most significant on cold starts and that it is related to corrosive combustion byproducts and oil film thinness, not “flow”. It seems to suggest a thicker oil may actually protect better on cold starts, as long as it is able to be pumped (you’re not starting below the minimum temperature for your oils winter grade).

Thread '75% of wear occurs at startup...'
https://bobistheoilguy.com/forums/threads/75-of-wear-occurs-at-startup.251019/

Wow.. great info...thanks

 

[Bojo]

In Australia most Mazda dealers use 10W-30 in these engines. No need to stress about 5W-30 at all.

Thats really interesting.. I bet the engines are quieter.. and is this in areas that get really cold?

 

[Bojo]

why not use 0w-20 in winter months and 5w-30 in summer times, Pennzoil Ultra Platinum is a fine oil (GTL base oil) to use or AMSOIL Signature Series , good mrv and ccs test results, quick flow is what you want on start-up. and yes there is about 70% wear at cold start up.

My reasoning is that Texas does not get hard cold winters where i am at if it gets to 20 degrees farenheit its rare.. it DOES get cold here , very cold at times but not like northern states.. so i figure why not just stick to the oil that seems to be better for wear overall.. thats my reasoning anyway

 

[Hohn]

Ok. I have to explain something, and ultimately I have a question at the end.

I decided, to use 5w30 INSTEAD of 0w20 for my new 2025 CX 5 Skyactive engine NON turbo. It calls for 0w20 , but due to cafe standards and many opinions, i went with 5w30 on my first oil change.


I live in Texas where its cold now but NOT brutal winters.

My reason for switching to 5w30 is because its supposedly provides slightly more wear protection overall, based on my research.Better for engine, not for cafe standards type of thing.


Having said all that, here is my question:

If it is true that 90 percent of engine wear occurs at STARTUP, and 0w20 gets to the engine QUICKER at startup, doing the math, does not this make the 0w20 a better choice then, no matter what tests show 5w30 is better overall (while driving etc)?



Make it make sense!

The benefit of faster oil pressure diminishes rapidly.

If you have oil pressure in 2 seconds, having it in 1 second adds essentially zero wear improvement. The rule of thumb I’ve seen in some literature is that anything under 3 seconds is essentially zero delay. So if you have pressure in under three seconds, then you have no wear reduction going to a thinner oil.

Thicker oils can actually have less startup wear because they leave thicker residual films behind at shutdown.

But it depends on 1) how cold is the “cold” start, 2) how long was the engine shut down before restarting, and 3) how thick was the oil when shut down.

Additive packs also matter a lot. A stout hit of moly can offset startup wear and make thick oil behave in startup wear like a thinner oil with less delay.

In reality, the difference between 0w and 5w is too small to matter until you get into VERY cold temperatures. If your typical “cold” start is near freezing and no worse, then anything up to 15w is basically thin enough for adequate cold start protection. After that, you need a good (moly-rich) additive packs to mitigate startup wear.