Why use 15/40 engine oil in a diesel.

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One thing I can't understand reading the forum posts is why so many people are using a 15/40 engine oil insted of a 5/40. I know it might be slightly cheaper, but is it just because they are uneductated enough to think thin oil causes trouble in cold temperatures, or is there some other reason?
 
I think part of it is this:

Diesel engines can be big heavy expensive things that make it cost effective to maintain the whole machine for a long time rather than just call it scrap when there are some minor mechanical problems. The whole machine is used for a long period of time so there are plenty of older units still in use. The older units, especially larger ones, tend to need a little warm up time before they function well and as such the difference between a 5W and a 15W isn't a huge issue.
 
All 40 weight oils are not created the same.
All 40 weight oils are not rated the same.

Many people here run a Synthetic 5w40 that is rated for that purpose, and I know that there are some syn-blends and full synthetics that are becoming more available in the 30 weight flavor.

I think sticking with a 15w40 is more about availability than anything else. You can find it anywhere. If you start looking for a 5w40 you won't see it on as many shelves.

Also, many many trucks are kept by maintenance managers that count every penny and haven't been able to figure out how making the switch would save after including all the involved costs of going to a synthetic product.
 
For most OTR diesels, cold starts are a small enough part of the equation that the difference between a costly Grp III 5W-40 and a less costly Grp II 15W-40 is nil.
Given the huge sump capacity of these engines, and the very satisfactory life from an engine run on a 15W-40, there is probably no overall cost savings to be realized by using a 5W-40, and more likely the 15W-40 is simply more cost effective overall.
If significant savings in fuel consumption could be realized with the use of a 5W-40, along with significant improvements in engine life, you can bet that fleet operators would be all over 5W-40s.
The savings in fuel and wear aren't there, though, so most fleets use 15W-40 oils.
 
Often times 5W40 has lower HTHS number (as allowed by SAE system that lumps 5W40 with 0W40 and 10W40) than 15W40, making 5W40 not as heavy duty as 15W40.
 
Originally Posted By: fdcg27

If significant savings in fuel consumption could be realized with the use of a 5W-40, along with significant improvements in engine life, you can bet that fleet operators would be all over 5W-40s.
The savings in fuel and wear aren't there, though, so most fleets use 15W-40 oils.


Exactly. 5W40 would only give fuel efficiency advantage under short trip service, that is not common in fleet operations.

But, I would like to know what fleets use in Alaska, Canada, Russia and similar places.
 
Originally Posted By: fdcg27
For most OTR diesels, cold starts are a small enough part of the equation that the difference between a costly Grp III 5W-40 and a less costly Grp II 15W-40 is nil.
Given the huge sump capacity of these engines, and the very satisfactory life from an engine run on a 15W-40, there is probably no overall cost savings to be realized by using a 5W-40, and more likely the 15W-40 is simply more cost effective overall.
If significant savings in fuel consumption could be realized with the use of a 5W-40, along with significant improvements in engine life, you can bet that fleet operators would be all over 5W-40s.
The savings in fuel and wear aren't there, though, so most fleets use 15W-40 oils.


I think Doug Hillary would disagree with you. He ran a large fleet of OTR trucks in Australia and used Delvac 1 synthetic 5w-40 with change intervals between 50,000 and 60,000 miles because it was cheaper than 15w-40 changed every 15,000 to 25,000 miles.
 
Maybe so.
There are larger fleets in this country, running many more trucks.
I'd be surprised to learn that any large fleet operator in the US uses 5W-40 over 15W-40, and their data is at least as good as Doug Hillary's.
Where did you get the idea that OTR trucks have 15K OCIs on 15W40 HDEOs?
They don't.
15K would be equivalent to 3K on a pax car using PCMO.
 
OK I can understand a truck operator in a warm climate using 15/40 because they don't have cold start problems and the engines are used for long periods, so the increased wear on initial start is not so important, BUT what I can't comprehend is the number of smaller truck and diesel car owners using 15/40. My own Volvo V40 had 15/40 used by a previous owner a few times.
You can buy good part synthetic 5/40 oils that are not much more expensive than 15/40 truck oil, it is only if you want to use an 0/40 that it must be an expensive full synthetic.
 
If I had a diesel car, and I used it as I do my current cars, I'd probably run 15W-40 summers and 5W-40 winters.
With my last diesel car, a W123 240D, which required, IIRC, only an API CF oil, I used 10W-40 winter and 15W-40 summer.
I'd likely use a 15W-40 summer and a 5W-40 winter now, based upon current oil availability as well as ease of starting.
For all year use, a 5W-40 would be very good for any diesel car, just a little pricier than a 15W-40.
A car is not an OTR truck in the way it's used.
If I ran the car at least a few hundred miles on each start, then 15W-40 would be the way to go, since a 5W-40 would provide no advantage.
 
Originally Posted By: jaj

I think Doug Hillary would disagree with you. He ran a large fleet of OTR trucks in Australia and used Delvac 1 synthetic 5w-40 with change intervals between 50,000 and 60,000 miles because it was cheaper than 15w-40 changed every 15,000 to 25,000 miles.


Let's think about why an oil goes "bad". Soot, TBN, oxidation or shearing.

Ox and shearing may offset each other, at least to a point.

Soot and TBN are important, but the big assumption here is that the 5w-40 has better soot and TBN retention characteistics than a 15w-40. That may be arguable.

Chevron argued in favor of the 15w-40 in an SAE paper from around 2001 with a very strong argument.
 
Hi,
this Thread is interesting

15W-40 has been the "standard" HDEO recommendation for heavy high speed US diesel engines for several decades. I'll relate my little story on this and not let it become tainted with Euro engine makers receommendations

I have used 15w-40 mineral HDEOs in a wide variety of US and Japanese engines since the early 1960s. This embraced a wide range of engine types, applications and a temperature range from around -15C to >40C.

During the 1990s Castrol trialled a semi-synthetic 15W-40 which was in an evolving prototype form in my engines (much like Formula 10W-60 some decades earlier). I was able to compare mineral 15W-40, SS 15W-40 and finally a fully synthetic 5W-40 HDEO in real time. The latter won out when based on the simple OTR operator's prime consideration - economics!

Many Fleet Owners will not experiment or upset the status quo. Their Technical people don't want to be exposed either. So guess what - no change - the 15W-40 HDEO remains alive and well as a great and dependable product

When carefully analysed, the 5W-40 synthetic combined with SS FF filter inserts and a centrifuge is a perfect mix for long life in OTR trucks. The benefits are very real indeed. Selling the concept to a very conservative Industry is considerably harder in practice!!

IMO it all comes back to operating economics in real terms
 
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Originally Posted By: friendly_jacek
But, I would like to know what fleets use in Alaska, Canada, Russia and similar places.


There is plenty of 15w-40 use up here. Even when it comes to winter use, those that do cold starts often just switch to a 10w-30 HDEO. There certainly are advantages, however, to being able to use one viscosity year round. For the heavy duty usage issue, as Doug Hillary mentioned, not everyone out there actually runs the tests and crunches the numbers to realize the benefit from the synthetic lubricants. Conventional 15w-40 under manufacturer recommended OCIs will work fine. Going beyond those limitations with a premium lubricant requires a little more effort than simply reading the manual.

Originally Posted By: skyship
...BUT what I can't comprehend is the number of smaller truck and diesel car owners using 15/40. My own Volvo V40 had 15/40 used by a previous owner a few times.


Why not? You mentioned that the price difference isn't that much. Well, it depends upon one's source, too. 15w-40 can often be had at a very attractive price.

Some people also choose not to use synthetics, or avoid them as much as is possible. People use 15w-40 conventional in applications that specify 40 grades for the same reason that people use 5w-30 conventional PCMOs in applications that call for 30 grades.
 
I don't believe that idling trucks is legal in the US now, but back when I was growing up and my father was a truck driver, they'd start the trucks and let them run for a month straight.

The reasoning was: on a cold winter weekend, it took too much time (and labor cost) to start a truck that had sat all weekend. It was cheaper to let the trucks run at 1000RPM (not idle) all weekend. Diesels use very little fuel at idle (compared to a gas engine of the same size).

With that said, a "cold" start wouldn't be needed in the winter which would negate one of the advantages of a 5-40 instead of a 15-40.

Other than that, I could think of the cost. While it's not a huge difference for those of us with 5-7 quart sumps, a truck uses gallons and gallons of oil. That small difference in one truck can make a difference; if you're running a fleet ... it can really makea difference.

Just some thoughts ... I could be (probably am) wrong.
 
Hi,
Miller88 - In my case(s) engines were never allowed to idle for long periods. In my own OTR vehicles idle timers were fitted but my professional Drivers were also limited to no longer than a 3 min idle time
This was monitored via the EMS - this is shown as a factor of "engine on" time. Most engine idling is simply a waste of fuel! Quick warm up is achieved via a quick drive off at reduced revs.

Idling can have an effect of fuel dilution too but this was never ever an issue except with some form of engine fault

When you are starting a cold engine containing around 40 litres of lubricant and large quantities of coolant behind the thermostat, good flow characteristics are very important. This is especially so if you subscribe to the quick drive off philosophy. Other than a suitable lubricant (perhaps 5W over 15W), this is BEST achieved via using SS FF cartridges and a centrifuge. Other less efficient choices exist of course

I found thet the 5W-40 synthetic HDEO was more tolerant of soot and retained its viscosity up to five or six times the use factor over the 15W-40 mineral base line. This factor with the SS 15W-40 was about 50% longer. A centrifuge may have contributed significantly to this result and I operated with OCIs at six times the Manufacturer's recommended OCIs

The 15W-40 viscosity HDEO has been a long time "save all" for heavy high speed US diesel engine users. IMO it will take a huge marketing effort to change this - well, except for a Warranty change by the US engine Manufacturers

In my case I will always use a 5W-40 over a 15W-40 if the economics stack up. Otherwise the 15W-40 version will do a great job

The Euro engine manufacturers generally have a lower viscosity requirement combined with longer OCIs!
 
Thank you for real good tips here!
Do you think similar logic works for both diesel and gasoline engines, that is using SS FF filter for best flow achievement ?

What brand/model/make SS FF filter do you recommend to use in the diesel and gasoline engines, respectively ?

Originally Posted By: Doug Hillary
In my case I will always use a 5W-40 over a 15W-40 if the economics stack up. Otherwise the 15W-40 version will do a great job

In your experience are the economics better for the 5W-40 because of 5-6 times longer OCIs or mainly due to the better fuel consumption with the 5W-40 versus the 15W-40?
 
Some very good advice for diesel fans from Doug, use a diesel rated 5/40 fully synthetic and some type of long life high performance oil filter system. It does make economic sense unless you pick a stupidly expensive Amsoil or Castrol product.
For my small 1.9D I have tried to find a better oil filter but no luck with Mobil, Amsoil, Royal Purple or WIX as they did not export diesel V40's to the US. The analyst at Blackstones said that my UOA at 10,000 km did indicate the filter was good for 20,000 km, so I will look at changing the oil type slightly next time from High Tech 5/40 Synthoil to Diesel Synthoil 5/40 to see what that does, before I increase the change interval to 15,000 km.

I would have thought there would not be much of a fuel consumption gain in using 5/40 rather than 15/40 unless you are short tripping. If I had a big truck using 15/40 I would look at a cheaper 10/40 first and see if it was as good as a 5/40 in UOA terms. There is something of a jump in price from a good part synthetic or HC dino oil to a group 4 full synthetic.

Originally Posted By: fpracha
Thank you for real good tips here!
Do you think similar logic works for both diesel and gasoline engines, that is using SS FF filter for best flow achievement ?

What brand/model/make SS FF filter do you recommend to use in the diesel and gasoline engines, respectively ?

Originally Posted By: Doug Hillary
In my case I will always use a 5W-40 over a 15W-40 if the economics stack up. Otherwise the 15W-40 version will do a great job

In your experience are the economics better for the 5W-40 because of 5-6 times longer OCIs or mainly due to the better fuel consumption with the 5W-40 versus the 15W-40?
 
Hi,
fpracha - Yous asked this:

"In your experience are the economics better for the 5W-40 because of 5-6 times longer OCIs or mainly due to the better fuel consumption with the 5W-40 versus the 15W-40?"

Measuring fuel economy in OTR heavy trucks is at best very difficult and at worst, impossible! There are simply two may variables and most organisations measure on a predetermined cycle such as weekly etc. Usually this is to identify mechanical faults, to prevent fraud and etc

In my own case I kept very good records but not good enough to determine the variance between the two lubricant viscosities

The average oil consumpion was around 6kkms per litre for the life of the vehicle(s) with me. So after 90kkms (OCI) around 12-15 litres had been used as top up

So yes the savings typically come from the extended OCIs - the cost of labour involved in OCs and the associated savings in lubricant, filters etc. And of course alleviating the inconvenience of downtime!

I found that mineral and semi-synthetic 15w-40 lubricants also went out of grade (thickened) at about double the recommended OCI - this would have had an effect on fuel economy too as the lubricants aged

People typically have very little idea of the hardship of doing OCs in the likes of Dozers etc. They can be high up on mountains, in deep snow etc etc. Extending service intervals in engines using HDEOs has many unpriced savings attached
 
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