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S/V "MACKINAC"
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My Universal M-30 diesel calls for 10w-40 diesel oil. Locally I can only find 5w-30 or 15w-40.
Can I substitute for another weight oil??? If so which way do I go. Living and sailing in Maine.
OR
Do I look around to find the right weight
Thanks
Bill
 

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All I can say is, I've been using Shell Rotella T 15w40 for the last 4 years in my Universal 5424, and the previous owner used it for about 10. I buy it from Walmart.

If you really want 10w40, Shell make Rotella T5, a more expensive synthetic blend, in 10w40. I can see the advantage being easier starting on very cold days, and you're in a colder climate than me.

Both are well-respected diesel oils.

Interestingly, I just fixed a noisy tappet in my Land Rover V8, with Rotella T. Took about 500 miles to work its magic.
 

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Corsair 24
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or delo 400....I stick with oils for the life of the engine or for the time I use said engine

switcing oils searching for the holy grail does no good and in some cases can cause excess sludge and or sediment

15-40 is fine in a 10 40 specd engine.

unless you are in freezing morning temps you are in the same temp range that calls for 10 40

good luck
 

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yeah Im no fan of synthetics for an old inboard diesel

if anything stick to dino stuff the delo 400 and rotella are so similar its funny...they are heavy and have nice amounts of detergents and anti shearing qualities.

if you are worried about wear previous to your ownership you can add some zddp like stp, or marvel mystery oil(those are the only 2 I have used and recomend) and call it good.

again stick to the same oil for the life of your engine especially if you have access to the same oil in your area...unless you move to another climate your good to go with 15-40

NOW BE WARNED this is the beginning of an oil thread, and wars start easily as soon as someone says only use this dont do that and never do this etc...

be warned! jajajaa
 

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Bill, 10W40 should be stocked at any auto parts store. And any gas station. If you don't see it and don't need to do the oil change today, any service station can order it in for you. That might mean buying a case (12 cans) but wtf, it won't go stale.

Usually you can go below the ##W end of the rating, a lower number just means easier starting in cold weather. And the higher number reflects typical operation, that's more important. If your engine calls for 40 and you use 30, it is under-protected in high temperatures. If you use 50, the oil stays too thick and you lose some economy and power. But if you are worried, the right oil certainly can be ordered in for you. Check a price versus mail order or Amazon just to make sure you're not being taken advantage of on that.
 

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I do think it's a good idea to use a diesel-focused oil like Delo or Rotella T, not just any 10w40. They have more of the detergents and surfactants to keep all that soot in solution. They also clean up a dirty engine, given time.
 

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Here's the most honest answer you will ever get. I have no idea if it's okay to use 15w40 over 10w40.

I also, don't believe many could know for sure.

What I do know is your manufacturer said to use 10w40 and I would believe them, unless they subsequently amended that advice.

For what it's worth, it may be helpful to understand how multi-viscosity oils work. Initially, there was only straight weight oil, which would lose some of their viscosity as the oil heated. Therefore, they would suggest a higher viscosity, so it would remain effective as motor heated up during use. However, that meant less lubrication at and near startup and multi-vis was born to address this. They start at lower vis and it rises as the oil heats. How? With chemical additives. Essentially, you are buying 10 or 15 w oil that has an additive that will increase viscosity with heat. Sort of.

So, your engine manufacturer thought that 10w was the right to get the motor up and running. Will 15w do the job. I don't know. You decide.
 

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of course it will

remeber this...the less difference there is between "weights" the longer that oil will last before breaking down

10.40 will last noticeably less at its correct "weight" before say a 20-50 or even a 15-40, this is visible even to the naked eye....

thats all Im going to say now...

10-40 is stocked almost anywhere

on an atomic 4 gas inboard any car 10-40 is ok, even moyer marine recomends this with a dash of marvel mystery oil

delo 400, rotella t are really good oil and I have noticed from using them in many vehicles from offroad motorcycles to old 4x4s that they last and keep their viscocity well

on old engines you neeed that as tolerances losen up as you age...

synthetics are the antitheses if viscocity retention over a period of time...they do however tolerate EXTREME HEAT better and they dont break downs as HARSHLY or quickly if you will

sooooooooooo if it where ME with your engine go for the 15-40 dino stuff and change regularly before any breakdown happens

and stick to that oil

good luck in your decision.

ps. minnewaska is absolutely right, DO NOT STRAY FROM WHAT THE MANUFACTURERS SAY TO DO as a general rule...unless that advice is obsolete...

this applies to oil technology, fuel, additives etc...this is a common question when restoring vehicles for example
 

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"They start at lower vis and it rises as the oil heats. How? With chemical additives. Essentially, you are buying 10 or 15 w oil that has an additive that will increase viscosity with heat. Sort of. "

Actually, the viscosity of a multigrade oil does fall off rapidly with temperature, it just doesn't do so as quickly as a with a single weight oil.

Take a look at this table for Mobil 1 0w40 (just a random example). Click on "tech details".

http://www.mobiloil.com/USA-English/MotorOil/Oils/Mobil_1_0W-40.aspx#

The viscosity is 75 cst at 40C, and 13.5 cst at 100C. Over 5 times thinner at 100C, than at 40.

A single weight oil would thin much more drastically, that's all.

All the viscosity modifiers can do is slow the rate of thinning with rising temperature.
 

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A caution note about using synthetics in an older diesel engine..

Using synthetic oils in older engines
I never suggested using a synthetic, I suggested a synthetic blend. There isn't enough synthetic in a blend for the engine to care at all, but it's the only way to get a 10w40 without use of lots of viscosity modifier.
 

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synthetic blends are hardly synthetic at all...

down here for my renault there are very few correct weight oils so I simply use a blend with great results...

also and Im curious what your manual states but you can use straight grade oils during certain times of years and or in climates that dont vary more than 20F...
 

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API Engine Oil Classification
SAE International

Actually it is easy to get more information on oil specs. The thickness ratings are from the SAE, they've got lots of files available. The complete rating, including spark-vs-combustion use (gas/v/diesel) and the alphabetical rating (i.e. "SF") some from them.

Any engine oil that was "top quality" 30 years ago, would be considered junk today. That's what the alphabetic ratings are about.

beaer in nind that any 10W40 oil actually IS a 15W40 oil, as the temperature comes up from the cold test point to the warm test point. The curves will meet and combine. So if your engine calls for 10W40, but you're using it in the tropics and it will never see sub-freezing temperatures? Yeah, 15W40 "is" the same thing for all intents and purposes.

Or, you get a bottle of 5W40 and a bottle of 15W40 and combine them. Might not be perfect, but the additives do average out. Beats using Crisco anyday.
 

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I would definitely stay with the viscosity recommendations in the manual. 5w- might be too thin. Oil types have changed, so you probably won't find the letter designations like CD, etc. I have used Rotella 10w- or 15w- for a few years now with no problems. I would stay completely away from synthetics in an old engine. They tend to get past old gaskets and seals. If you search the archives, we have discussed this before and I think I posted a link to a website with the equivalent letter designations-old to new.
 
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Mermaid Hunter
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All I can say is, I've been using Shell Rotella T 15w40
I agree. Shell Rotella is one of the few remaining fleet oils that have both a CD and SM ratings. I have six gas engines and two diesels. I buy Rotella 15W40 and run it in everything.

I did a lot of research before making this decision and consulted with some friends (crew) that run agricultural equipment leasing companies.
 

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auspicious youd be surprised how many offroad motorcycle racers swear that rotella t is the only oil they use too

its not just for cars and trucks and diesels
 
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