Rethinking 5w-40 vs 15w-40 for my low use diesels

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JHZR2

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Ive been a user of 5w-40 HDEO since around 2003. Before Delvac 1 was reasonably available in the US, I took advantage of occasional trips to Canada, where they sold it in Walmart routinely.

Fast forward, much has changed except for the types of diesels I run. Older school designs, Mercedes OM616/617, OM603, and Cummins 5.9L.

Back when I ran my Mercedes diesels all over in all conditions. So having a quality 5w-40 in the winter when I could encounter subzero cranking in locations far from home with no block heater was appealing, especially since the original Delvac 1 was considered quite a superior product.

Fast forward a bit, less use of the old diesels for routine transport, more for the enjoyment of driving these old, well made cars. So in other words, they may sit long times, and they will likely only get used when conditions look good and I’m of the mind to run them. To date, I’ve still used 5w-40 in the Mercedes cars, because they sit, and though I don’t need the cold flow advantage, I do want the fast flow after extended sit times.

In my Cummins trucks, they’ve both had 15w-40 since I’ve owned them. I have run Kirkland 15w-40 in my 2wd, 442k mile truck because I figure it’s an old, high mileage truck, and Kirkland seems cheap and good. My nicer, lower mileage 4x4 truck has Rotella T4 15w-40 in it, and that’s what got me to thinking about it…. Maybe I should just run Rotella T4, or Kirkland 15w-40, or a 5w-40 hdeo for the fleet.

I’m frugal, but the reality is that some of these vehicles will see OCIs of two years or more. The cost delta though I need many gallons across all vehicles, isn’t going to make or break me. But is it really worthwhile, given how good run of the mill 15w-40 HDEOs have gotten, to run 5w-40 in any of these vehicles, since they are all effectively hobby/collector/personal hauling vehicles. I don’t rely on them for work or to earn my pay, they don’t see conditions that are challenging, and the oil will get changed on calendar time over mikes or running hours for the most part.

Just seems like it could be a waste to run 5w-40 in all these when 15w-40 is proven and the chances of very cold starts are nil. 15w-40 conventional seems like the better value, unless the startup flow at reasonable ambient temperatures and long sitting periods is much better, making cold start wear much lower.

What woukd you do? Thanks for reading!
 
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15w40 has improved drastically and are the most superior oils and should be considered a universal oil for all internal combustion engines.

Use 15w40, it is cheap, superior, and a proven long life oil in either conventional or synthetic form.

It shall never give up until the day you decide to change the oil.
 

JHZR2

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15w40 has improved drastically and are the most superior oils and should be considered a universal oil for all internal combustion engines.

Use 15w40, it is cheap, superior, and a proven long life oil in either conventional or synthetic form.

It shall never give up until the day you decide to change the oil.

Agree it’s good stuff, fine for most uses. My use includes sitting for months at a time, so the flow performance seems like the more important parameter. An oil that flows faster, fuel use to get it to flow aside, is better for me.
 
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If you don't need the cold start capability of a 5W-40, I would use a 15W-40. Might leave more of a film on cams, etc. for the next start, after sitting for a long time.
At work we've had a few Cummins 1 tons that do nothing but heavy towing, with 350,000 miles or more on them. All they have ever seen is bulk 15W-40 from a few different suppliers over the years. They get used in some very cold weather here too; plugged in overnight but sitting outside.
 
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How much less will 15W-40 across all those vehicles cost you annually versus 15W-40 in only the Cummins engines and 5W-40 in the rest of them? 15W-40 will be fine in those old MB Diesel engines anyway. They aren't exactly fragile or picky.
 
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JHZR2

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How much less will 15W-40 across all those vehicles cost you annually versus 15W-40 in only the Cummins engines and 5W-40 in the rest of them? 15W-40 will be fine in those old MB Diesel engines anyway. They aren't exactly fragile or picky.

If I estimate right, the diesels I own take about 12 gallons total. Say the price difference is $6/gal, it comes to $72/OCI. Somewhat less per year since not all get an annual OCI.

Im doing it less for the money, more for the consolidation to a single product, and because it does bug me a bit that maybe it is a big waste to run 5w-40 in any of them.

The answer to my question is not economic, it’s startup flow and reduction of cold start wear after sitting for six months or more.
 
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Ive been a user of 5w-40 HDEO since around 2003. Before Delvac 1 was reasonably available in the US, I took advantage of occasional trips to Canada, where they sold it in Walmart routinely.

Fast forward, much has changed except for the types of diesels I run. Older school designs, Mercedes OM616/617, OM603, and Cummins 5.9L.

Back when I ran my Mercedes diesels all over in all conditions. So having a quality 5w-40 in the winter when I could encounter subzero cranking in locations far from home with no block heater was appealing, especially since the original Delvac 1 was considered quite a superior product.

Fast forward a bit, less use of the old diesels for routine transport, more for the enjoyment of driving these old, well made cars. So in other words, they may sit long times, and they will likely only get used when conditions look good and I’m of the mind to run them. To date, I’ve still used 5w-40 in the Mercedes cars, because they sit, and though I don’t need the cold flow advantage, I do want the fast flow after extended sit times.

In my Cummins trucks, they’ve both had 15w-40 since I’ve owned them. I have run Kirkland 15w-40 in my 2wd, 442k mile truck because I figure it’s an old, high mileage truck, and Kirkland seems cheap and good. My nicer, lower mileage 4x4 truck has Rotella T4 15w-40 in it, and that’s what got me to thinking about it…. Maybe I should just run Rotella T4, or Kirkland 15w-40, or a 5w-40 hdeo for the fleet.

I’m frugal, but the reality is that some of these vehicles will see OCIs of two years or more. The cost delta though I need many gallons across all vehicles, isn’t going to make or break me. But is it really worthwhile, given how good run of the mill 15w-40 HDEOs have gotten, to run 5w-40 in any of these vehicles, since they are all effectively hobby/collector/personal hauling vehicles. I don’t rely on them for work or to earn my pay, they don’t see conditions that are challenging, and the oil will get changed on calendar time over mikes or running hours for the most part.

Just seems like it could be a waste to run 5w-40 in all these when 15w-40 is proven and the chances of very cold starts are nil. 15w-40 conventional seems like the better value, unless the startup flow at reasonable ambient temperatures and long sitting periods is much better, making cold start wear much lower.

What woukd you do? Thanks for reading!
My work truck is an 05 Ford 6.0 diesel. I work for a small private company and the boss lets me take it home and use it if I need to on the weekends within reason of course hauling feed from town to my house 3-4 miles. Anyway the only thing he asks in return I change oil in it and the company buy it. No big deal it was up for an oil change and he said go get 15 quarts of napa 10w40. Apparently that’s all the truck has ever had since brand new. Never seemed right dumping it in but I do what I’m told I reckon. Gets a motorcraft filter though 😃
 
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15W-40 is a better oil. . It would be my choice but All I have now is a tractor that is diesel and I do once a year oil changes and the 5W-40 is for winter starts to plow the snow or if the wife grades the arena.
 
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Only reason i don’t use 15w40 is because of the winter use here. Otherwise I would use it year round.
 
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I switched to Mobil Delvac 1300 15W40 in my 2012 Cummins Ram a couple years ago. I was having shearing problems with the Mobil Delvac ESP 5W40. I have not had issues since. I use the block heater in my truck on winter nights for extra help and drive it any day the high will be above 0F in Iowa.

I just recently bought 12 gallons of 15W40 Mystik JT8, that will be on tap next... Plenty of semi's using 15W40 on the road's these days...

Just my $0.02
 
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OP's location states New Jersey. That region has very long and cold winters if I'm not mistaken. I know eastern PA gets harsh winters often sub-zero. I lived in Philadelphia about 20 years ago when we had 4 feet of snow dumped on us in a few days. That winter was brutally cold.

A 15w motor oil in the winter would be a big mistake IMO. Go watch the cold flow of a 15w testing after it's been frozen overnight. It's like honey. Very slow to move.

In any region that get near freezing I'd go with a 5w oil. Period. Absent some proof that a 15w is better somehow, which it seems is not the case considering the most engine damage occurs at cold startups. A 15w is going to cause more damage than it will help over a 5w.
 
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