Consequence of switching oils, winter vs summer

[johnmyster]

Six month changes work well for me. Honestly, I could probably use 15w-40 all year, or 5w-40 all year.

Question, is there any tribological reason to avoid alternating 15w-40 summer and 5w-40 winter? I'd likely stick within a brand: Delo XSP or Delvac ESP/Extreme.

Is there potential that I'm actually accelerating wear by alternating additive packages that compete with each other?

Our heavy towing is mostly in the summer, which the 15w gives me extra mental margin against fuel dilution, high temperatures, etc. 5w makes me feel better about winter starts when/if it's frosty outside. Owners manual sets a lower threshold of 0F for the 15w. Subject engine is Cummins 6.7, solid lifter.

 

[Jetronic]

does the engine always get up to temperature when you start it in winter, or do you do short runs?

 

[demarpaint]

Run the 5W40 from either brand all year. Makes life easy and will be perfectly fine in VA.

 

[Cujet]

I don't think there is any downside to your oil change plan. Your oil is robust enough to not be reliant on the additive package to prevent metal to metal contact. While a good quality 5W-40 should suffice all year round, there is no question a modern 15W-40 is more shear resistant, with it's higher base viscosity.

 

[GRUMPYDUDE2]

Run the 5W40 from either brand all year. Makes life easy and will be perfectly fine in VA.

This is what I would do . Changing grades from summer to winter may have helped decades ago, but, todays oils are so much better at cold/hot protection its not going to matter.

 

[kschachn]

It’s the fact that its a 40-grade oil that may help with fuel dilution, not that it happens to have a particular winter rating.

And the truly tiny increase in wear that might exist from switching brands is utterly inconsequential. I’ve switched brands probably 50 times on my old Sienna “sludge monster” engine and so far no exceptional consumption. As others have said just use the 5W-40 year-round.

 

[Urshurak776]

+10 on running the 5W-40 weight year round. It's fine.

 

[johnmyster]

It’s the fact that its a 40-grade oil that may help with fuel dilution, not that it happens to have a particular winter rating.

And the truly tiny increase in wear that might exist from switching brands is utterly inconsequential. I’ve switched brands probably 50 times on my old Sienna “sludge monster” engine and so far no exceptional consumption. As others have said just use the 5W-40 year-round.

I get that they're both "40" but the reported HTHS and hot viscosity is always higher for the 15w than 5w.

Switching oils is literally zero extra effort, so that is not the basis of the question. I presently have both grades of Delo on the shelf, for instance.

does the engine always get up to temperature when you start it in winter, or do you do short runs?

It gets some short runs all the time despite not being a daily driver. Long trip towing the travel trailer to our destination, lots of short trips in the area, then long run home. Rince and repeat.

 

[JohnnyJohnson]

About the same as changing you brand of TP!

 

[Jetronic]

I get that they're both "40" but the reported HTHS and hot viscosity is always higher for the 15w than 5w.

Switching oils is literally zero extra effort, so that is not the basis of the question. I presently have both grades of Delo on the shelf, for instance.

It gets some short runs all the time despite not being a daily driver. Long trip towing the travel trailer to our destination, lots of short trips in the area, then long run home. Rince and repeat.

I would always go for the highest winter grade that's suitable. I want the oil to get warm ASAP in winter, diesel engines have more blowby and no pcv so water contamination is a concern.

 

[johnmyster]

I would always go for the highest winter grade that's suitable. I want the oil to get warm ASAP in winter, diesel engines have more blowby and no pcv so water contamination is a concern.

Understood. I'm skeptical that thicker oil gets heated faster on warmup, enough to matter. I'm not sure I buy this as sole motivation to run 15w vs 5w which flirting with or below the manufacturer's specified temperature threshold for grade.

This particular engine sits for a week at a time or more in the winter. My impression of the cummins 6.7 is that substantial drain down occurs on the oiling system. The motivation for 5w in the winter would be cold start lubrication.

 

[kschachn]

Understood. I'm skeptical that thicker oil gets heated faster on warmup, enough to matter. I'm not sure I buy this as sole motivation to run 15w vs 5w which flirting with or below the manufacturer's specified temperature threshold for grade.

This particular engine sits for a week at a time or more in the winter. My impression of the cummins 6.7 is that substantial drain down occurs on the oiling system. The motivation for 5w in the winter would be cold start lubrication.

Yes it does warm up faster. There is increased shear heating which heats the oil faster. But that's only generally true dependent on the specific oil and the temperature.

But it isn't that simple in regards to the winter rating. It's completely dependent on the temperature and the specific oil, one oil being thinner than another is only guaranteed at the temperature at which the winter rating is tested. Above that there is no guarantee.

For example, you often see someone say that they want an oil with a 0W rating because it will be better for startup. This is only guaranteed below about -30 or so for an oil with a 0W rating, above that temperature it may be thinner or thicker than one with a 5W rating.

It just isn't universally true that the winter rating in and of itself determines when an oil is thinner or thicker - only at the testing temperature for that rating.

 

[edhackett]

I get that they're both "40" but the reported HTHS and hot viscosity is always higher for the 15w than 5w.

Always? Really? Here's the data from Chevron's PDS sheets for the XPS oils:

5W-40: 15.4 4.2
15W-40: 14.8 4.1

Ed

 

[johnmyster]

Always? Really? Here's the data from Chevron's PDS sheets for the XPS oils:

5W-40: 15.4 4.2
15W-40: 14.8 4.1

Ed

Yeah, Delo XPS is an oddity like that. I've asked that question before:

J

Thread 'What do we know about Delo 400 XSP?'

Mar 4, 2025

Granted, these formulations have been out for some time, but...

Delo XSP 15w-40 - Looking at the PDS:

• Published pour point is much lower than Rotella T6 and Delvac Extreme, 15w-40s. On par with 5w-40s. Are they not using the ASTM D97 method?
• Cold crank viscosity of 4600 (-20 C) agrees with the above - Rotella and Delvac are 6300/6100. (Are they not using ASTM D5293?)
• The 40 C viscosity is in line with the other 15w-40 full syns.
• If the differences are real, what does it tell us? "Better" base stock for a 15w40 that performs better at extreme cold?

...

• johnmyster
• Replies: 19
• Forum: Heavy Duty Engine Oil (HDEO) - Diesel Vehicles

• 

 

[johnmyster]

Yes it does warm up faster. There is increased shear heating which heats the oil faster. But that's only generally true dependent on the specific oil and the temperature.

But it isn't that simple in regards to the winter rating. It's completely dependent on the temperature and the specific oil, one oil being thinner than another is only guaranteed at the temperature at which the winter rating is tested. Above that there is no guarantee.

For example, you often see someone say that they want an oil with a 0W rating because it will be better for startup. This is only guaranteed below about -30 or so for an oil with a 0W rating, above that temperature it may be thinner or thicker than one with a 5W rating.

It just isn't universally true that the winter rating in and of itself determines when an oil is thinner or thicker - only at the testing temperature for that rating.

I'm going to say shear heating is negligible, or at least it's not a first order contribution to engine warmup.

I also get that viscosity isn't linear vs temperature, and different formulations may not be universally thicker or thinner across the warmup range. It doesn't stop engine makers from saying 15w-40 if never below 0F, and then 5w-40 if so.

I also got to clean up three gallons of rotella 15w-40 that amazon delivered in broken bottles in the bitter of last winter, and I know that it's a good bit thicker at Virginia cold than the 5w40 I had on hand at that same temperature. Perhaps that's also negligible to an engine's lube system, but I had hands on with the science experiment.

 

[Vexorg]

My 2014 has had only 5w40 Brotella its entire life and I see no reason to change it to 10w or 15w. I am however going away from Brotella as the bulk price at the dealer has gone through the roof recently, so I will just use the shop at work and do them on my own.

 

[kschachn]

I'm going to say shear heating is negligible, or at least it's not a first order contribution to engine warmup.

I also get that viscosity isn't linear vs temperature, and different formulations may not be universally thicker or thinner across the warmup range. It doesn't stop engine makers from saying 15w-40 if never below 0F, and then 5w-40 if so.

I also got to clean up three gallons of rotella 15w-40 that amazon delivered in broken bottles in the bitter of last winter, and I know that it's a good bit thicker at Virginia cold than the 5w40 I had on hand at that same temperature. Perhaps that's also negligible to an engine's lube system, but I had hands on with the science experiment.

For the oil to warm up it is. It’s why if you want the oil to warm up as quickly as possible you keep the RPM as high as practical.

And yes I’d agree that an oil with a 15W winter rating is likely to be thicker than one with a 5W rating in “Virginia cold”.

 

[johnmyster]

For the oil to warm up it is. It’s why if you want the oil to warm up as quickly as possible you keep the RPM as high as practical.

The oil pump puts more heat into cold oil across a full warmup cycle than pistons, the oil cooler, turbo center section, egr cooler, head and block contact, etc?

Still, the question stands regarding alternating 5w vs 15w additive chemistries and if they're close enough to be inconsequential within a brand or across brands.




Looks like a 6bt oil pump is rated 16 gpm max. I'm going to guess that's ~3000 rpm, and light acceleration/cruising in my truck is half that. Since Zee06 tells us that PD pumps don't have slip, we'll assume it's linear. 8gpm at 80 psi (assume constant full bypass cold oil, which is a pretty BIG conservatism) is 278 watts. So the pump is doing 278 watts of work on the oil. 1/3 of a horsepower.

But wait, the delta between work done on the 15w vs 5w is only the pressure delta between the two oils across the warmup temperature transient. So only a fraction of the 278 watts. I'll go out on a skinny limb and say the pumping work contribution to heating the oil is an order of magnitude (or more) below the total heating rate.

Shear heating in all the bearing surfaces across the surfaces/bearings in the engine is...for the purposes of this thread uncalculatable. We'd just need to look at all the BITOG expert threads that say the MPG improvement from thinner oil are trivial to verify that the parasitic losses (parasitic heating) are trivial in the grand scheme of an engine that gets 12-15 mpg during warmup.

 

[kschachn]

Anywhere there is shear heating. I thought that was untrue as well, but I was shown on here that it is the number one mode for heating the oil. RPM, not engine load, is what will heat the oil. It gets more complicated when there are oil coolers (which also can heat the oil).

If you really want to run the oil with the 15W winter rating, then do so. You seem to have made that decision.

 

[johnmyster]

But again, none of this has to do with the question I proposed.

I thought that was untrue as well, but I was shown on here that it is the number one mode for heating the oil. RPM, not engine load, is what will heat the oil. It gets more complicated when there are oil coolers (which also can heat the oil).

Did said discussion include light truck diesels with the contribution of piston cooling? Lots of gas engines don't have piston squirters. In that case, friction/shear and conduction from block/head being the only heat contributions into the oil. I don't disagree that lube oil is the primary means of cooling (removing heat of friction or oil shear from) the rotating assembly. I just diagree that the rotating assembly is the main source of heat into the lube oil for the subject application.

Relevant diesels can't survive without piston cooling due to combustion chamber in the piston.

O

Thread 'Sources of engine heat and effects of oil viscosity'

Oct 12, 2018

in general, what % of engine heat is generated by viscous shearing, combustion or friction? Anything else terminology wise? Is viscous shearing a component of friction which is causing the heat, and heating up the oil which is heating the block ...

I always thought that most of the engine heat is from combustion ... viscous shearing was mentioned in one the recent threads on this forum and made me wonder about the percentages.

my final question and as much as I enjoy it,

it is not my intention to turn this into thick vs. thin...

• OilUzer
• Replies: 66
• Forum: Passenger Car Motor Oil (PCMO) - Gasoline Vehicles

If this is the source of your perspective, then I agree, interesting data. It was a 1.7L SI engine, so no combustion chamber in the piston and likely no piston jets. Even then, at 2000 rpm no load, shear heating of oil falls to equivalent of other sources at the 3 minute mark.

I was told on BITOG that higher viscosity always means higher film thickness, which always means less wear. Here's my reference: https://bobistheoilguy.com/forums/threads/is-mobil-1-0w-40-too-thin.397705/post-7333593

Let's just say I'm wrong. On a typical drive cycle, hypothetically I get 15w-40 oil and coolant to stable operating temperature in 10 minutes. How long does it take with 5w-40?