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#2673736 - 07/04/12 03:03 PM Why use 15/40 engine oil in a diesel.
skyship Offline


Registered: 06/09/12
Posts: 2071
Loc: Tettnang, Baden-Wurttemberg, G...
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?

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#2673753 - 07/04/12 03:14 PM Re: Why use 15/40 engine oil in a diesel. [Re: skyship]
yonyon Offline


Registered: 03/06/12
Posts: 3492
Loc: NJ, USA
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.

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#2673762 - 07/04/12 03:17 PM Re: Why use 15/40 engine oil in a diesel. [Re: skyship]
SuperDave456 Offline


Registered: 10/29/08
Posts: 2249
Loc: Dallas, Texas
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.

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#2673785 - 07/04/12 03:38 PM Re: Why use 15/40 engine oil in a diesel. [Re: skyship]
JHZR2 Offline



Registered: 12/14/02
Posts: 33531
Loc: New Jersey
Depending upon the use, a straight 40wt can also be a prudent choice.

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#2673815 - 07/04/12 04:23 PM Re: Why use 15/40 engine oil in a diesel. [Re: skyship]
fdcg27 Offline


Registered: 09/25/09
Posts: 9195
Loc: OH
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.
_________________________
12 Accord LX 22K HGMO 0W-20
09 Forester 64K PU 5W-30
02 Accord 127K G-Oil 5W-30
01 Focus ZX3 98K Synpower 10W-30
95 BMW 318iC 146K Defy 10W-40

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#2673844 - 07/04/12 05:11 PM Re: Why use 15/40 engine oil in a diesel. [Re: skyship]
friendly_jacek Offline


Registered: 05/04/03
Posts: 5217
Loc: southeast US
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.

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#2673845 - 07/04/12 05:14 PM Re: Why use 15/40 engine oil in a diesel. [Re: fdcg27]
friendly_jacek Offline


Registered: 05/04/03
Posts: 5217
Loc: southeast US
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.

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#2673853 - 07/04/12 05:23 PM Re: Why use 15/40 engine oil in a diesel. [Re: fdcg27]
jaj Offline


Registered: 08/21/03
Posts: 893
Loc: Vancouver, Canada
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.

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#2673863 - 07/04/12 05:35 PM Re: Why use 15/40 engine oil in a diesel. [Re: jaj]
fdcg27 Offline


Registered: 09/25/09
Posts: 9195
Loc: OH
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.
_________________________
12 Accord LX 22K HGMO 0W-20
09 Forester 64K PU 5W-30
02 Accord 127K G-Oil 5W-30
01 Focus ZX3 98K Synpower 10W-30
95 BMW 318iC 146K Defy 10W-40

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#2673871 - 07/04/12 05:48 PM Re: Why use 15/40 engine oil in a diesel. [Re: fdcg27]
skyship Offline


Registered: 06/09/12
Posts: 2071
Loc: Tettnang, Baden-Wurttemberg, G...
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.

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#2673881 - 07/04/12 06:04 PM Re: Why use 15/40 engine oil in a diesel. [Re: skyship]
fdcg27 Offline


Registered: 09/25/09
Posts: 9195
Loc: OH
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.
_________________________
12 Accord LX 22K HGMO 0W-20
09 Forester 64K PU 5W-30
02 Accord 127K G-Oil 5W-30
01 Focus ZX3 98K Synpower 10W-30
95 BMW 318iC 146K Defy 10W-40

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#2674071 - 07/04/12 09:23 PM Re: Why use 15/40 engine oil in a diesel. [Re: jaj]
JHZR2 Offline



Registered: 12/14/02
Posts: 33531
Loc: New Jersey
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.

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#2674247 - 07/05/12 04:30 AM Re: Why use 15/40 engine oil in a diesel. [Re: skyship]
Doug Hillary Offline


Registered: 05/30/03
Posts: 4828
Loc: Airlie Beach Australia
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



Edited by Doug Hillary (07/05/12 04:30 AM)
_________________________
Regards
Doug

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#2674384 - 07/05/12 09:04 AM Re: Why use 15/40 engine oil in a diesel. [Re: friendly_jacek]
Garak Offline


Registered: 12/05/09
Posts: 11182
Loc: Regina, Saskatchewan, Canada
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.
_________________________
Plain, simple Garak.

2008 Infiniti G37 coupe - Mobil Delvac 1 ESP 5w-40, Hastings LF113
1984 F-150 4.9L six - Quaker State GB 10w-30, Wix 51515

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#2674699 - 07/05/12 01:56 PM Re: Why use 15/40 engine oil in a diesel. [Re: skyship]
Miller88 Offline


Registered: 04/09/08
Posts: 6328
Loc: Onondaga County
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.
_________________________
'11 Focus PYB 45K
'00 Cherokee PYB 125K

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