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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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  #31  
Old 09-15-2009
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So RichH, maybe you can answer my question. My new-to-me 1979 Volvo MD11C came with very specific oil recommendations by the engineers who designed it. I'm in your camp that the engineers are the experts (which is why I follow my Honda recommended oil change interval in my Honda, not the Jiffy Lube profit based 3K interval). They recommend 20W30 for my engine. After a couple of weeks of looking, I gave up and put in Rotella 15W40.

What would you use (include brand name and vendor) in an engine where the engineers recommend 20W30?

Harry
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  #32  
Old 09-15-2009
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The suffix portion of the engine oil designation is the important one - the "30" for the 20W**30**. The suffix number is the required viscosity designation when the engine is at full designed operating temperature, not just the 'oil/water' temperature but the WHOLE engine. When the engine is at full operating temperature the clearances will be at the precise as designed distances, and the oil (at proper viscosity/pressure) will be properly 'supporting' those clearances, etc. The Prefix number is the apparent viscosity of the oil at ambient (cold) temperatures. The prefix number (viscosity at ambient temp.) allows less 'starting torque/friction' during the start-up process, and since the clearances are less at ambient than at operating temps. you develop the pressure (in the bearings) needed to support the hydrodynamic bearings ... faster. Most engine wear probably occurs during the start-up phase, when the colder engine temperatures have thermally 'shrunken' many of the clearances; if you dont want the higher friction, possible increased surface, etc. wear on an expensive engine .... then install a "pressure pre-oiler" in which the oil pressure (causing the bearings to be fully supported by the oil) is electrically (or manually) gained before any rotation of the engine parts - done on all the time on very 'expensive' engines. If you dont pressure pre-oil then the simple 'rules of thumb' developed nearly 140 years ago still apply .... "dont apply full load on any IC engine until its up to normal operating temperature" (and all the clearances have opened to proper dimensions). Ive used pre-oilers since I was a pup ... and routinely get 'several/many hundred thousand miles' out of an automobile engine (engine 'bottom', not valves and 'accessories', etc.). Should one use a pre-oiler on a marine engine? .... probably not $$ worth it as the typical boater only 'starts' the engine several time a YEAR and once started the engine runs at 'constant speed' and constant temp. for a comparatively long time - 'steady state' operation is 'very good' for an engine.

To answer your question ..... The manufacturer specified 20W30. If your engine is not starting up from below freezing temperatures, then ANY oil with a viscosity rating at '30 suffix' will be OK .... 5W30, 10W30, 20W30, straight 30 wt. will be suitable (the best match-up would be 10W30, in your case). Again, simply dont run hell out of the engine at WOT until the engine 'totally warms up' !!!!!!!!!!!

Another FAQ ... my engine is old, should I use a heavier oil ... the oil pressure is lower than when new? Probably not! Have a (very knowledgeable) mechanic check and possibly reset the oil back pressure valve so that the proper pressure (back to 'spec'.) is maintained in the journals ... if you cant maintain the oil pressure via pump adjustment (cant do this on many small engines), then its really time to 'rebuild the bottom' of (or replace) the engine as those designed clearances have 'opened up' due to adverse wear.

Moral: use the oil SAE grade 'as specified' (especially the 'suffix' number), dont run hell out of the engine until its fully warmed up.

Do I use synthetics? ... Yup, keeps the generated particles from combustion in suspension better, better handles the adverse 'chemistry' from the combustion (blow-by) process better, does deposit some 'chemicals' to the surface friction areas for better wear protection. BTW I use LARGE/oversized recirculation lube oil filters ... the largest surface area filter that will fit.
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  #33  
Old 09-15-2009
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"If the original engine designer was clever enough to realize that the film strength of a certain viscosity oil "
Good answer 40 year ago but, like Bohr's Atom, a bit behind the times. As it was explained to me, by an engineering dean who made his income from a long list of combustion-related patents (he gets paid a bit every time a diesel-electric locomotive is built, among other things), what counts is not simply viscosity nor "film" lubrication. But, rather there is thick-film lubricaiton, and thin-film lubrication. And in the case of journal bearings, thick-film lubrication only counts when there is still oil flooding the bearings, i.e. during a hot restart. Once the oil has drained--and it must drain unless you keep the bearings immersed and foam the oil during regular operation--all that is left is a VERY THIN FILM of oil. At that point "thin film lubrication" is what counts, not viscosity.
There are oils, mainly synthetic oils with expensive additives, that literally harden up and turn into a sheet of glass when they are "struck" with a heavy load in the thin-film scenario. With these oils, or with this type of property, when your bearings start to slam around (and they always literally slam around during startup, before there is a thick film) they slam into a thin film of oil, which promptly acts like a sheet of glass, lubricating and protecting far better than any conventional oil could.

SAE ratings? all well and good, but I'm reminded of the Army commercail that showed a Bubba announcing "Ahs could hardly change the earl in mah car, but now the Army dun taught me to maintayn this heayh Apache helicopter!" (Yeah, well, remind me never to stand under one he's worked on while it is aloft. )

Even the SAE's own web site will tell you that the oil rating (i.e. SD, SF, SM) says things that can be more important that the viscosity number. Viscosity counts--but no more than any one card in a winning poker hand.


"dont run hell out of the engine until its fully warmed up. " And for that we can thank sailors, in particular the United States Navy. Until they wrote a procurement specification for cars/trucks back in the 1940's, there was no standard for warm-up times. Then someone decided it would be nice if the targets could get moved around a bit more quickly when under attack. IIRC the original spec called for full and operational oil pressure within 20 seconds of start-up. Debates over heat loads, head gaskets, and other reasons to wait ten minutes can begin after that.

Last edited by hellosailor; 09-15-2009 at 10:33 AM.
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  #34  
Old 09-15-2009
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Hello - I think your hyperbole is showing tad too much. As one who actually designed/engineered such bearings, etc. and with a quite stong engineering tribology knowledge to boot, I'll stand by my statements. Thin film lubrication is of course important, but in the case of marine engines where comparative absolute time to need to protect the static friction phase of startup ... is minimal as a total. More marine, etc. engines have been ruined because of incompatible/inappropriate VISCOSITY oil, than ......... 'additives'. I'll stake my engineer/scientist's reputation on that one.
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Well, Rich, it all comes back to the question of what can you do when the oil the manufacturer recommends may not be available, or not conveniently available.

He can buy 0W20 or 0W30, but 20W30 may be like hens teeth. You don't have to believe that 0W30 is better than 20W30 in every way. Maybe in a 40-year old dino oil it isn't.

But in a highly engineered synthetic? OK, tell the guy to mail order his 20W30 from an industrial supplier in Irkutsk, if that's the only place to find it. The point of the question was, originally, WHAT DOES HE DO WHEN HE CAN'T FIND THE OEM SPEC OIL?

"Find it anyway" would not be a useful answer to most of us.
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I gave the best answer I could based on many years of actual technical/scientific/engineering experience: Use oil that has the 'suffix' number as specified and the closest (& next lower) prefix number .... whats the point of discussion of you fail to have any appreciation/comprehension/acknowledgement of that. The oil viscosity is dependent on temperature and if the operating temperature of the engine is at spec. for the 'suffix' number of the SAE oil rating then the engine will perform AT spec. This is not politics where the strongest and most developed 'presentation' and loudest voice 'wins'; this is just plain, simple FACT that is and has been accepted for the past 140 years. Unless you can intellectually present some supported and well document hydrodynamic 'anomaly', etc. to the contrary ... I simply dont intend to continue any further discourse on the matter. ;-)
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  #37  
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Rich,

My question remains, and politics and engineering (I happen to be a Mechanical Engineer by degree, but oils are NOT my specialty) aside, reality comes into play. I understand the first number can run as low as possible, but where does one buy a 30 weight diesel oil? Rotella, arguably the best (or certainly a solid player in the game -- I don't want to start THAT argument!) only sells one multi-weight, and that is 15-40. In synthetic, I can get 5-40, but it's still 40. They sell single weight 30, but in a sailboat where a significant number of engine cycles are under 10 minutes (yet another problem, but is it better to shut it down cold, idle it until warm, or drive in circles to warm it up under load so you can shut it down?), the first number is fairly important. Ah, life is full of compromises. And as an engineer, I want "the single, only, provable right answer!"

Harry
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  #38  
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This is a great discussion. I use synthetics exclusively in all my vehicles and boat. The only two 'readily' or 'regularly' locally available synthetics are the Rotella 5W-40 and the Mobil 1 5W-40 (Mobil is also the Delvac Synthethic, as I understand).

RichH or Hello, given these two choices, which is the preferred oil lube and why? Or, should the sailors who choose to use synthetics in marine applications try to source a different type online, etc. For this discussion, we can assume the manuf recommendation is SAE30, which I think is typical of most sailboat marine engines. It is in my Yanmar.

Jason
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  #39  
Old 09-15-2009
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I just had to click on this when it got to 40 responses. It's oil, and you change it every 100 hours hopefully. Rotella 15-40 is approved by everyone, Delo (diesel engine lubricating oil) is also great oil. End of story. They will work in your engine.
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  #40  
Old 09-17-2009
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JRD - thanks for bringing the discusssion back down a notch. I have the 28 year old Volvo whose instructions specify 20wt. No one, including Volvo sells 20wt. I have read and truly appreciate all the responses - adds to my knowledge - but I figure I'm doing harm by not deciding on something. I doubt I'll ever start the engine from below 32F but I do sail into the late fall and early spring. Since I have never changed the oil and don't know what is in it now, I want to decide on one and stay with it (I like to minimize mixing brands and types). I got some Delo 400LE 15W40 but will probably take it back and get some Rotella T 15w40. All the mechanics I had talked to said they would use straight 30wt. but from the sounds of things here, the 15 in the 15w40 should give me better protection when starting and warming up. That is my current plan - thank again to all.
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