engine oil

[Kogut]

I have a 2009 and a 2004 ram 2500 pickup one with a 6.7 and a 5.9 liter engine . In the owners manual of both trucks they say to run 15w-40 in the warm weather and to run 5w-40 synthetic in cold weather. My question am I better off to run 5w-40 synthetic all year round?

 

[AH64ID]

If you live somewhere that needs cold weather oil then yes, it’s best to stick with one brand/weight of oil...at least that’s my opinion.

There are also some great synthetic 15w-40’s out there that have similar cold weather pour points and some other benefits over 5w-40, but they generally cost more.

 

[Ozymandias]

5-40 is fine all year round if you want that, no matter what climate it is. There is no harm of any kind by using it.

 

[Jim W]

I run 15W-40 all year, I do not change to the 5W-40 Synthetic oil in the winter months. I have never changed to a lighter grade of engine oil in any vehicle that I have owned since my first 1969, 1500CC Air Cooled VW Beetle car. The reason the automakers suggest the lighter weight engine oil is for easier starting in supper cold temperatures. The automakers do not know what region the tuck will be operated in such as Alaska or Florida. So, they generalize on the side of easier starting in the winter months by recommending a lighter grade of oil for winter operation.

Depending on where you live you may not need to change to the lighter weight oil at all. In the mid-west with the significant temperatures swings during the winter months we have seen in the last couple of years 15W-40 oil will work with no issues.

Another reason why I keep 15W-40 oil in all year round is my oil changes usually occur every 6-months and not mileage any more. This works out for me that I usually change the engine oil in March and again in Sept. Also, the truck is kept in a garage all year except when we are traveling.

Or as OZZY has stated run 5W-40 all year.

 

[Kogut]

thank you for your input. I been running 15w-40 year round and when temperature here in R.I. gets really cold I plug the block heater in and have not any issues starting in the morning. I'll continue using 15w-40 all year long.

 

[AH64ID]

I did a freezer test some years back with 15w-40 Delo and 15w-40 Amsoil. At -10°F the Delo was THICK, too
thick for me. The Amsoil flowed really well. I had the video posted, but lost it when photobucket went to a fee program.

Bottom line, the guide in the owners manual for 15w-40 above 0°F is very accurate and not arbitrary. So as long as your cold starts are above that then don’t worry about it. That’s for dino based 15w-40’s.

 

[JR]

Bottom line, the guide in the owners manual for 15w-40 above 0°F is very accurate and not arbitrary. So as long as your cold starts are above that then don’t worry about it. That’s for dino based 15w-40’s.

The temperature recommendation in the Ram owners manual is intriguing. I have a 2017 B series 6.7 CM2350 book and it plainly spells out 15w40 as acceptable to lower temps. Its recommendation for synthetic is for "ambient temps consistently below -13*F".

While I understand your concern for the colder temps I grew up on a large dairy farm that is still in the family. I also know alot of farmers in the area. Nobody, and I don't use that word lightly, has ever used synthetic oil in their farm equipment. Fleet spec 15w40 is the norm, not the exception. Even my cousins new tractors (2019) still spec conventional 15w40. It drops below zero quite frequently here with the exception of the last 2-3 years. There are tractors on our farm that I learned to operate 30 years ago that were well worn at the time and still in operation today. Some were even the Case tractors with the CDC engines (Consolidated Diesel Corporation, a Cummins/Case joint venture). All these years of conventional oil and still running well. Well, most of em anyway

About the only change at those temps is making sure they are plugged in. Otherwise, it probably wouldn't matter if there was diesel in the crank case

 

[AH64ID]

Being plugged in is huge. While it doesn’t directly hear the oil pan it will radiate heat to the oil and it doesn’t have to make it hot, just not ambient cold.

What temp does that manual call for the block heater?

After my rebuild I ran conventional 15w-40 for a while to break it in. The rebuild was completed in December, so all winter it had conventional in it. Starting at about 25° oil pressure was noticeably slower to build. I ran my oil pressure gauge in port just above the ECM, which I believe is in the cam journal. A couple of colds starts around 10° and the engine tone is different from low oil flow too. All of that is unplugged.

Now I can’t quantify any additional wear out of those cold starts, but I do know how it sounded and how slow the pressure was too build.

The biggest advantage to synthetic is when you can’t plug it in.

 

[JR]

Interestingly I've not seen anything on block heater recommendations. I do agree with you 100% on that it is huge regardless of o. If it's down into the 20's, which is quite often here, I'm plugged in if I can help it. Aside from the obvious benefits of starting a warm engine it's substantially easier on batteries and starters, plus it minimizes the need for any unnecessary engine idling to allow for warm up time beyond a minute or two while I clear windows off.

Even on vehicles that don't come with block heaters from the factory get them. VW's, tractors, etc. I've got timers in both garages and on the side of the garage where I park. Always a place to plug in

 

[Jim W]

I always plug in the truck every night from Nov 1 till March 15 of every year with a 4-hour timer, but the VW is never plugged in.

 

[AH64ID]

I always plug in the truck every night from Nov 1 till March 15 of every year with a 4-hour timer, but the VW is never plugged in.

I plugged the truck in on work nights with a 90 minute timer when I drive it daily (90 minutes got me 90% of the coolant temp I would with an 8 hour plugin), but at just over $0.06/hr I didn’t make it a regular routine if I wasn’t going to be driving. Luckily it sits in a shop now where the lowest I’ve seen it get is 19° even when it’s close to 0° out.

 

[MichaelOverfield]

I recently did some looking into what the numbers actually mean. The SECOND number is the viscosity, so both 5w-40 and 15W-40 are the same viscosity when the engine is running at temperature.. the same, because the second number is warm viscosity. Here is the interesting part, the first number is not viscosity, it is pour point, and it refers to a temperature.. so 5W will pour at 5 Degrees, and 15W at 15 degrees.. in other words, you have a larger temperature band with 5W-40, but same hot engine performance with either. So, there is absolutely no benefit to 5W-40 over 15W-40.. read that slow, no benefit.. with the caveat.. if you are running synthetic, real synthetic. Conventional oils require all kinds of special additives to get the low temperature pour points, and I'm not even sure a conventional oil can attain 5W-40, because that is a thick high temperature oil with a low temperature pour point, something conventional oil just does not do well.. so in most cases the 15W-40 conventional oil requires many additives to attain that 15 degree pour point, where a really good synthetic will have a low pour point without any additives needed.

 

[MichaelOverfield]

I have a 2009 and a 2004 ram 2500 pickup one with a 6.7 and a 5.9 liter engine . In the owners manual of both trucks they say to run 15w-40 in the warm weather and to run 5w-40 synthetic in cold weather. My question am I better off to run 5w-40 synthetic all year round?

Short answer, YES. 5W-40 will be some kind of synthetic oil and in all ways superior to any 15W-40 oil. The "40" is the running viscosity. The "15" and "5" refer to pour points at cold temperatures, so the 5 will pour at 5 degrees and above, the 15, at 15 degrees and above.

 

[Tuesdak]

Long answer is a Taxpayer funded military study on how long it takes to get oil pressure at the furthest point in an oil gallery in Arctic temperatures. Soot makes a big difference esp. in the dirty engine the study used. There may be a reason here for the 6 month oil change of soot accumulation.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a382457.pdf

 

[AH64ID]

I recently did some looking into what the numbers actually mean. The SECOND number is the viscosity, so both 5w-40 and 15W-40 are the same viscosity when the engine is running at temperature.. the same, because the second number is warm viscosity. Here is the interesting part, the first number is not viscosity, it is pour point, and it refers to a temperature.. so 5W will pour at 5 Degrees, and 15W at 15 degrees.. in other words, you have a larger temperature band with 5W-40, but same hot engine performance with either. So, there is absolutely no benefit to 5W-40 over 15W-40.. read that slow, no benefit.. with the caveat.. if you are running synthetic, real synthetic. Conventional oils require all kinds of special additives to get the low temperature pour points, and I'm not even sure a conventional oil can attain 5W-40, because that is a thick high temperature oil with a low temperature pour point, something conventional oil just does not do well.. so in most cases the 15W-40 conventional oil requires many additives to attain that 15 degree pour point, where a really good synthetic will have a low pour point without any additives needed.

That's not exactly what the 5W and 15W mean, they too are viscosity.

A 5w-40 acts like a 5 weight oil when cold and a 40 weight oil when hot, and will pour a HECK of a lot colder than 5°.

Oil viscosities are often referenced at 40°C and 100°C, and on the same scale cSt.

So lets look at 3 oils.

15W-40 Valvoline Premium Blue Conventional Oil has a 100°C viscosity of 15.1, a 40°C viscosity of 118, and a pour point of -30°C.
15w-40 Amsoil DME Synthetic Oil has a 100°C viscosity of 15.6, a 40°C viscosity of 112.4, and a pour point of -40°C.
5w-40 Amsoil DME Synthetic Oil has a 100°C viscosity of 15.4, a 40°C viscosity of 94.5, and a pour point of -43°C.

As you can see at operating temps they are all similar and the 5w has a cold advantage. Now compare the pour point of the 15w's and you can see how being synthetic has a large impact on pour point for the same multi-grade rating.

This chart shows how the viscosity relates to the cSt number.

Short answer, YES. 5W-40 will be some kind of synthetic oil and in all ways superior to any 15W-40 oil. The "40" is the running viscosity. The "15" and "5" refer to pour points at cold temperatures, so the 5 will pour at 5 degrees and above, the 15, at 15 degrees and above.

5w-40's will not be superior to any 15w-40 in all ways. The bigger spread you get in a multi-viscosity oil the more likely you are to have weight loss as represented in the NOACK Volatility test. In the two Amsoil's listed above the 5w-40 has a 9.2% weight loss and the 15w-40 only has 5.1%, which is a common separation from 15w-40 to 5w-40.


Additionally most 5w-40's are slightly thinner at operating temp than their 15w-40 counterpart. It doesn't take much to see a difference on a oil pressure and temperature gauges. When I switched from a 15w-40 with a 100° viscosity of 15.0 to one with 15.6 the pressure went up a few psi and the average temp was lower.


You also generally get better High-Temperature/High-Sheer scores when the viscosities are closer. 7% higher on the 15w-40.


The only benefit to the 5w-40 in these two oils, same series, is the 3°C lower pour point.. it's not even enough to make a difference at the temps most of us see.


So by no means is a 5w-40 oil always better than any 15w-40, there is a very distinct reason I run a full synthetic 15w-40, as it has numerous advantages over a the 5w-40.

 

[MichaelOverfield]

That's not exactly what the 5W and 15W mean, they too are viscosity.

A 5w-40 acts like a 5 weight oil when cold and a 40 weight oil when hot, and will pour a HECK of a lot colder than 5°.

Oil viscosities are often referenced at 40°C and 100°C, and on the same scale cSt.

So lets look at 3 oils.

15W-40 Valvoline Premium Blue Conventional Oil has a 100°C viscosity of 15.1, a 40°C viscosity of 118, and a pour point of -30°C.
15w-40 Amsoil DME Synthetic Oil has a 100°C viscosity of 15.6, a 40°C viscosity of 112.4, and a pour point of -40°C.
5w-40 Amsoil DME Synthetic Oil has a 100°C viscosity of 15.4, a 40°C viscosity of 94.5, and a pour point of -43°C.

As you can see at operating temps they are all similar and the 5w has a cold advantage. Now compare the pour point of the 15w's and you can see how being synthetic has a large impact on pour point for the same multi-grade rating.

This chart shows how the viscosity relates to the cSt number.

View attachment 126200




5w-40's will not be superior to any 15w-40 in all ways. The bigger spread you get in a multi-viscosity oil the more likely you are to have weight loss as represented in the NOACK Volatility test. In the two Amsoil's listed above the 5w-40 has a 9.2% weight loss and the 15w-40 only has 5.1%, which is a common separation from 15w-40 to 5w-40.


Additionally most 5w-40's are slightly thinner at operating temp than their 15w-40 counterpart. It doesn't take much to see a difference on a oil pressure and temperature gauges. When I switched from a 15w-40 with a 100° viscosity of 15.0 to one with 15.6 the pressure went up a few psi and the average temp was lower.


You also generally get better High-Temperature/High-Sheer scores when the viscosities are closer. 7% higher on the 15w-40.


The only benefit to the 5w-40 in these two oils, same series, is the 3°C lower pour point.. it's not even enough to make a difference at the temps most of us see.


So by no means is a 5w-40 oil always better than any 15w-40, there is a very distinct reason I run a full synthetic 15w-40, as it has numerous advantages over a the 5w-40.

Good data, pour point is not the correct way to express the point I was trying to make.. the first number with the w is for "winter" and it is for a low temperature performance.. of course viscosity is what affects the ability of an oil to flow, but the 5W does not mean it is a thin oil when cold that gets thick when hot, that is pretty much impossible. It's always at least a 40wt viscosity, not thinner at lower at low temperatures, rather it will still flow like a 5wt, or 15wt standard single viscosity oil at those temperatures when a straight 40wt oil at those temperatures would be getting tar like.

Lubrication and cooling, it's vital that the oil can flow through the pump and get to the surfaces that need it.. if your oil is super thick it might be good in a gear case where it is just splashed around, loss of efficiency aside, but it's not going to help you if your pump can't move it from the oil pan to where it's needed.

If you read the note in the manual posted a few posts back, when it warns about lower viscosity oil it refers to an oil with a lower number after the "W", not before. The warm condition is most demanding and limiting from a lubrication standpoint, if your oil retains sufficient viscosity to be called 40 in the second number, it should meet all demands of they application. The lower first number gives you cold weather performance, and if your flow is not happening because your oil won't flow, there is no way you can tell me that is not going to accelerate engine wear, it will.

I found this article interesting.. though I think the calculation at the end is a bit ridiculous.

Having said that, unless it is really cold, most people could use either 5W-40 or 15W-40 and not have any noticeable difference, the bigger issue would be what base stock and additives are in that oil, that takes more digging to understand the differences.

https://www.machinerylubrication.com/Read/204/multigrade-oil

Here is one on the history of the rating system and what the numbers mean.

https://www.lardoil.com/wp-content/uploads/2018/12/Multi-Grade-Oils.pdf