Oil Viscosity Basics: 0w40 vs 5w30 Cold Start

[GW.]

Forget about the grade and focus on the winter rating for cold starts. It’s all about the ability to crank and pump in a pressurized oiling system. There’s no gravity lubrication going in your engine and no reason to pay attention to oil races…

5W is good down to around-25f to -30f. Below that 0W.

 

[BISCUT]

Early on I moved from Mobil 1 0w20 to Mobil 1 5w30 in my 15 F150 5.0. I'm in northern NH & VT in winter enough to see some double digit -F numbers. 5-30 has done well. I write this as I have pondered 0-40 but never found the need. Now your post has me interested, as your application is a GTDI.

 

[GI_GRIFF]

Early on I moved from Mobil 1 0w20 to Mobil 1 5w30 in my 15 F150 5.0. I'm in northern NH & VT in winter enough to see some double digit -F numbers. 5-30 has done well. I write this as I have pondered 0-40 but never found the need. Now your post has me interested, as your application is a GTDI.

Mobil 1 has a little higher quality oil on the Walmart shelf. That oil is the 0W-30 ESP version. The 0W-30 has more PAO base stock in the blend than their 5W-30, plus it has a >3.5 HTHS Euro spec, higher than the 5W-30 HTHS. What you are using is fine, I just thought you may like to know this info.

 

[brandon9715]

Early on I moved from Mobil 1 0w20 to Mobil 1 5w30 in my 15 F150 5.0. I'm in northern NH & VT in winter enough to see some double digit -F numbers. 5-30 has done well. I write this as I have pondered 0-40 but never found the need. Now your post has me interested, as your application is a GTDI.

Reason I’m running 0w40 in my 5.0 is for a better HTHS while towing heavy occasionally while also simplifying my oil stock to less variants. So far 0w40 has done very well both in my 5.0 and my dad’s 2.7, but always looking to optimize things. Overkill for my 5.0, but necessary for the 2.7 and 3.5 imo.

 

[colloyd00]

I’m trying to learn and I can’t find an answer to this. And I’d like to change the OP’s hypothetical just a bit: let’s compare a 0w30 to a 10w30 for my question and let’s make it 10* F outside when the vehicle starts. Both oils can flow at this temp but the 0w30 is “thinner”. Intuition tells me that 0w30 is better at startup. And this AMSOIL post supports that theory: https://blog.amsoil.com/should-i-sw...MIyu3Vt7ekkgMVTEr_AR2FUyBMEAAYASAAEgL8ePD_BwE

But if I’m understanding this thread correctly, on cold (or any) startup; the oil pump will pump the same volume of oil even though the 10w is thicker. And then, ultimately, cold start wear/properties at my 10* hypothetical is more intrinsic to the oil itself than its *w rating. Which I think is what @Hohn is getting at in this thread https://bobistheoilguy.com/forums/t...00-miles-2011-gx460-1ur-fe-175k-miles.403490/

Am I understanding the concepts correctly?

 

[AJB0009]

I was going to start a thread this morning, but it is along these same lines.
Forgive me, I don't want to "hack" this thread, so let me know if this is okay.
~
We are preparing for an ice storm and likely power outages. I have an older 5kW generator. It has Napa Full Synthetic High Mileage 10W-30 in the sump right now. If the temp drops down to, let's say, 5 F, can I still pull on the recoil rope and start it just fine? Would it be a noticeable difference if I had 5W-30 in the sump?
Second, when that generator is running, if it is under load, it runs pretty hot. Is there any protection difference between 5W-30 and 10W-30. What about if it was summer, say 90F?

 

[Hohn]

I’m trying to learn and I can’t find an answer to this. And I’d like to change the OP’s hypothetical just a bit: let’s compare a 0w30 to a 10w30 for my question and let’s make it 10* F outside when the vehicle starts. Both oils can flow at this temp but the 0w30 is “thinner”. Intuition tells me that 0w30 is better at startup. And this AMSOIL post supports that theory: https://blog.amsoil.com/should-i-sw...MIyu3Vt7ekkgMVTEr_AR2FUyBMEAAYASAAEgL8ePD_BwE

But if I’m understanding this thread correctly, on cold (or any) startup; the oil pump will pump the same volume of oil even though the 10w is thicker. And then, ultimately, cold start wear/properties at my 10* hypothetical is more intrinsic to the oil itself than its *w rating. Which I think is what @Hohn is getting at in this thread https://bobistheoilguy.com/forums/t...00-miles-2011-gx460-1ur-fe-175k-miles.403490/

Am I understanding the concepts correctly?

If the oil is thin enough (< ~5000cP) it will flow sufficiently quickly to get your oil films re-established without excess startup wear. Until those films are established, the protection has everything to do with the additives and NOTHING to do with viscosity. Moly and your EP wear additives are what are saving you in that interim, and the viscosity is irrelevant until the oil pressure shows up and then the films are re-established.

If you have poor EP/AW additive packages, thinner viscosity can’t save you. And if you have robust EP/AW, thicker oil doesn’t hurt you to a point. (< 5000cP).

At 10F, there’s only a modest difference oil pressure rise and film establishment between 0w and 10w. You need to go significantly colder for those two grades to show a major disparity.

Keep in mind that since there’s no cold viscosity below 0w, a 0w-20 or 0w-30 will have much lower cranking viscosity when cold than a 0w-40 even though they all meet 0w. If it existed, the 0w-20 might be more like -5w or a -10w.

I was going to start a thread this morning, but it is along these same lines.
Forgive me, I don't want to "hack" this thread, so let me know if this is okay.
~
We are preparing for an ice storm and likely power outages. I have an older 5kW generator. It has Napa Full Synthetic High Mileage 10W-30 in the sump right now. If the temp drops down to, let's say, 5 F, can I still pull on the recoil rope and start it just fine? Would it be a noticeable difference if I had 5W-30 in the sump?
Second, when that generator is running, if it is under load, it runs pretty hot. Is there any protection difference between 5W-30 and 10W-30. What about if it was summer, say 90F?

Most small generators are splash lubricated so you aren’t turning an oil pump with the recoil rope. That’s why the pull start ability is about the same between 5w and 10w.

You might notice a difference just because the oil residue in the bearings and rings will be thicker, so the 10w will be harder to pull. Enough to notice, likely not enough to mean you can’t start it. Your physical strength is a factor I cannot account for.

There’s no protection difference really between 5w-30 and 10w-30 because the difference between them that would matter would be in the additives, not the common 30 grade viscosity. In theory the 10w would have a thicker base oil and slightly higher HTHS. In practice, it’s just a cheaper base oil with no real protection advantage.

The NAPA in the sump will do just fine to protect you year round.


A splash lube engine benefits from a No-VII formula. Heck, I run Valvoline VR1 20w-50 in my splash lube engines because it’s designed specifically for low foam, low friction, low detergency, etc. There’s a lot of overlap IMO between what makes a good race oil and a good small engine oil.

 

[AJB0009]

Excellent information, thank you sir.

 

[twX]

Is a 0w40 more viscous at 0C than a 5w30 at 0C (or vice versa)? I’m seeing conflicting information.

The 0W-40 will still have a higher viscosity at 0°C. The temperature might have to get pretty close to -30°C before the 0W-40 would be thinner. Even then, the difference might only be equivalent to around 2 or 3°C, since 0W-40's will almost always be formulated to just barely meet the CCS requirement for a 0W, whereas many synthetic 5W-30s are pretty close to meeting the 0W requirements.

The 5W-30 will flow better during the vast majority of cold starts, but it shouldn't matter very much. Cold start bearing wear is only significant if it takes >15 seconds for the bearings to start receiving oil. On most engines, this won't be the case even at the CCS test temperature. There are exceptions for some engines, mainly large diesel engines that have a whole lot of oil volume to make up after a cold start.

 

[Nuclear_42]

Im running Amsoil Signature Series 0w-40 in my 2024 GMC 1500 5.3 and Amsoil XL 5w-30 in my 2021 Subaru Outback 2.5. Both vehicles have been starting fine -20 deg F past few days in Minnesota. If that doesn’t help you make a choice then we’d have to ask a member in Siberia.

 

[twX]

But if I’m understanding this thread correctly, on cold (or any) startup; the oil pump will pump the same volume of oil even though the 10w is thicker.

That's only the case for a short period of time after the engine starts, before the oil pump's pressure relief valve opens. Within a few seconds after an engine start, enough back pressure will have built up that the oil pump PRV will open, and at that point the 0W oil will have a much higher flow rate than the 10W oil. With the thicker oil, the PRV will also up open up sooner, reducing the flow before as much oil has been pumped.

 

[BMWTurboDzl]

....There’s no gravity lubrication going in your engine and no reason to pay attention to oil races…

Would you think there's a difference with regards to how quickly the pumped oil returns to the pan?

 

[GW.]

Would you think there's a difference with regards to how quickly the pumped oil returns to the pan?

That’s a good question. Based on oil pressure I’ve personally never seen an oil pump starved for oil and I live where it gets well below zero.

 

[Hohn]

The 0W-40 will still have a higher viscosity at 0°C. The temperature might have to get pretty close to -30°C before the 0W-40 would be thinner. Even then, the difference might only be equivalent to around 2 or 3°C, since 0W-40's will almost always be formulated to just barely meet the CCS requirement for a 0W, whereas many synthetic 5W-30s are pretty close to meeting the 0W requirements.

The 5W-30 will flow better during the vast majority of cold starts, but it shouldn't matter very much. Cold start bearing wear is only significant if it takes >15 seconds for the bearings to start receiving oil. On most engines, this won't be the case even at the CCS test temperature. There are exceptions for some engines, mainly large diesel engines that have a whole lot of oil volume to make up after a cold start.

Those large diesels generally have prelube cycles that run before starting.

 

[Hohn]

That's only the case for a short period of time after the engine starts, before the oil pump's pressure relief valve opens. Within a few seconds after an engine start, enough back pressure will have built up that the oil pump PRV will open, and at that point the 0W oil will have a much higher flow rate than the 10W oil. With the thicker oil, the PRV will also up open up sooner, reducing the flow before as much oil has been pumped.

PRV open at low Idle? If this happens (and that’s me raising eyebrows in skepticism), it certainly does not last long because cold, thick oils takes a lot shaft work to pump at the PRV cracking pressure, and all that shaft work shows up as viscous oil heating, about 200w worth of heat at high idle with 5000cP oil at a 7 bar relief.

 

[twX]

PRV open at low Idle? If this happens (and that’s me raising eyebrows in skepticism), it certainly does not last long because cold, thick oils takes a lot shaft work to pump at the PRV cracking pressure, and all that shaft work shows up as viscous oil heating, about 200w worth of heat at high idle with 5000cP oil at a 7 bar relief.

The oil pump PRV will be open at cold idle rpm on any engine, even when the oil viscosity is only 50 cP.

Viscous heating in the oil pump does help a lot when the oil is very thick, and when the vast majority of the oil is just recirculated through the pump continuously due to the very low flow rates. It will still take minutes of idling for the oil temperature in the main gallery to increase by, say, 30°C, and in cold weather it needs to heat up a lot more than that before PRV closes.

 

[Japanese]

Would you think there's a difference with regards to how quickly the pumped oil returns to the pan?

That’s a good question. Based on oil pressure I’ve personally never seen an oil pump starved for oil and I live where it gets well below zero.

I was trying to imagine how that would even happen when @Hohn mentioned it once.

The engine has at least 3-4 qt of oil. The oil pick up tube is at the lowest part of the pan/sump. I'm sure the engine is designed to have at any time at least 1/2 the amount of that oil in the sump. The sump always has larger volume than the volume of all engine oil passages altogether. If that is true, than there is no chance to be more oil in circulation than the oil in the sump at any given moment. So in that case the oil pick up would never starve.
Are these thoughts logical enough?

We exclude lateral G forces when the oil in the sump may go side to side at sharp corners, mostly at a race track.

 

[oil pan 4]

So I have a question about how viscosities correlate to temperature ranges in real world use. I recently read that while a 0w40 meets pumpability requirements at the -35C to -40C range that outperform a 5w30, the 5w30 often has lower viscosity around 0C than the 0w40. I had thought that a 0W oil would outperform a 5w oil for cold flow at pretty much all temperatures below 40C. If that is not the case, is the common BITOG member recommendation of Mobil 1 0w40 in place of a 5w30 in many gasoline truck engines actually causing more engine wear on cold starts?

Going a grade lower on the big number makes more different at those intermediate cold temperatures than a 5w or a 0w.
For example. I recently switched my air compressor over from 10w-30 in the engine and straight 30wt in the compressor to 0w-30 in the engine and straight 20wt in the comp.
I left the 0w-30 and the straight 20wt out over night and it was 15f the next morning.
At +15f the straight 20wt was definitely more viscous than the 0w-30.
I'm sure at -15f it would be a completely different story at least with new oils.

 

[oil pan 4]

PRV open at low Idle? If this happens (and that’s me raising eyebrows in skepticism), it certainly does not last long because cold, thick oils takes a lot shaft work to pump at the PRV cracking pressure, and all that shaft work shows up as viscous oil heating, about 200w worth of heat at high idle with 5000cP oil at a 7 bar relief.

The best guidance I've found was someone on here posted a jeep service bulletin recommending changes in oil viscosity for cold temperatures. I figured this might be useful. If I applied this to my vehicles I'll never need to think twice about cold starting damage. But I was never going to be able to remember all those temperatures and grades.
After a good hunt and peck session with all the different grades and temperatures it all boiled down to jeeps new drop dead cranking viscosity is around 6,000cP.
Apparently this one engine was snapping oil pump drive shafts in the cold. New jeeps are trash and I avoid them but I found the recommendation interesting and potentially useful.

Small pull start engines are more like 500 to a thousand cP.

 

[pbm]

Mobil 1 has a little higher quality oil on the Walmart shelf. That oil is the 0W-30 ESP version. The 0W-30 has more PAO base stock in the blend than their 5W-30, plus it has a >3.5 HTHS Euro spec, higher than the 5W-30 HTHS. What you are using is fine, I just thought you may like to know this info.

Mobil 1 ESP 0w30 was going to be my advice as well. The >3.5 HTHS gives you the 'protection' you seek while the '0' winter rating gives you the 'pumpability'. The fact that it's so reasonably priced at Walmart is a bonus.

OT: How is your dad's 2.7T holding up? How many miles, mpg's etc?....I've read that it's a very good engine while also being fuel efficient. If I were to buy a pickup I'd look for one with that engine.