Still confused about oil viscosity

[robdsuzuki]

I know that loads of people use 15w Rotella. I have used it for years as well. I now have a 1982 GS750TZ 12,000 miles. Manual calls for 10w40. It's getting cold here in Louisville, KY. Why do we use a 15W when the manual calls for 10W?? Is it because there is so little diff between 10W and 15W? Thanks. RD

[Nessism]

15W is fine until it's really cold outside - below the temp most riders can tolerate. If you are worried you could always go to 5W-40 Rotella synthetic.

[Normk]

I generally hate oil threads because there is so much non-sense posted by people with little applicable training and little or no appropriate experience. Posts by people who have read the results of various web searches proliferate to the amusement or annoyance of people who have training and experience. Rant off.

Let's take the risk of trying some oil stuff in this groups as some groups are very sensible, let's hope...

I am a retired Canadian Interprovincial automotive tech, journeyman partsman, marine, motorcycle tech., Power Engineer, shop foreman, service manager, parts manager, automotive/heavy equipment/motorcycle/small engines/marine college instructor, fleet manager, etc. so have some training and experience which have been sufficient to keep me employed. My experience has varied from the Far North to the tropics so have some variability in applications.

None of the above is to assert that I know it all but simply to indicate that I have been required to show competency to those who pay for that value. Sorry if I sound "testy" on this subject but, quite simply, I am testy and seldom can be convinced that it is worth while to post on the subject. In the hope that the perspective is useful to someone....

One of my most strongly held views is that home mechanics tend to use oils of too high a viscosity for the application conditions. People misunderstand the role of oil pressure and seem to believe that heavier/thicker oil provides better lubrication but this is not true. One can easily see the truth of this assertion if the conditions are taken to the cold end of the spectrum.

Take an engine at minus 30 F, using SAE 30 oil and time the interval required from start-up until oil is flowing from the last camshaft bearing onto the lobe. Truly frightening! We had to shut down research engines because the camshaft bearings were screaming, smoke rising and still no oil. Use a "10" weight or "10W-30" and the oil delivers to the bearings & lobes quite quickly but not to be compared to a "5" or better a "0" base weight oil. Smoke still eminates from some camshaft bearings during cold start with "10" base weight oils. Oil pressure is always at or above the oil pressure relief valve setting so high pressure is present but no lubrication is ocurring at the camshaft bearings with the thicker oil but quite good to excellent lubrication by the 5 and 0 oils, all-be-it at lower oil pressure.

Another example would be a Kawasaki KLR650 engine which is a very robust design which is well represented on the roads. Check oil pressure on a KLR and it will be seen that a typical cold start at 50 or 60 F with recommended oil viscosity base weight indicates 80+ PSI of oil pressure at the test port. OK, so if high pressure equals lubrication then the conditions should be ideal, right?

Test a KLR engine with recommended oil (same oil or any other base weight within the recommended range) which is warmed up and running down the highway and oil pressure is in the 10 PSI range which is normal for this engine. Pull the cover and the oil fly-off from the valve train is like a fire hose. These engines endure for large mileages in tough conditions and the maker chooses to use these design parameters so....

In short, no oil flow produces maximum oil pressure but no lubrication. Run an oil base weight which actually provides sufficient oil flow to the required areas and forget the silly heavy oil stuff!

When choosing oil weight, one will almost certainly wish to use a multi-grade oil which has a wider viscosity range than that of a single viscosity oil. In fact, motorcycle manufacturers never recommend a single viscosity oil (i.e. SAE 30) but always a multi-grade (i.e. 10W-40) oil in order to provide for sufficient oil flow when cold but in order to maintain sufficient oil pressure when hot.

OK, so if oil pressure doesn't lubricate, why do we need oil pressure at all?

Let's consider the KLR650 as it is fairly fresh in my memory from some research conducted a few years ago. The engine has 80 PSI oil pressure when cold and around 10 PSI when normally warmed up so 10 PSI is all the pressure which is "needed" if we believe that moving parts are actually supported by a pressurized oil cushion as do some people. Silly, but let's keep that in the equation because it actually relates to what is needed but is a misunderstanding.

That engine has a relatively open and short oil flow passage from oil pump to crankshaft main and connecting rod bearings but a long and quite small diameter oil flow passage to the upper cylinder head and the camshaft bearings & lobes. These areas are critical to low oil supply because they lack rolling elements and sliding friction quickly suffers from low oil supply.

Why have the oil pump limited to a bit over 80 PSI when less than 10 PSI supplies sufficient oil to the top end?

OK, the problem is that the oil is thick at cooler temperatures and so doesn't flow as easily and so requires much more pressure/push to move it through the passages at sufficient flow rate in order to supply the top end. Using 10W-40 oil and timing the oil pressure reduction against temperature reveals that it takes a significant interval before the oil warms enough that the oil pressure drops off to near 10 PSI. Using 0W-40 and the oil pressure drops quite quickly.

Check oil flow to the top end and both are throwing lots of oil but the 0W-40 is a real fire hose, even when cold. Don't even try that in your garage! (VBG)

In short, it takes high oil pressure to make the oil flow to the top end when cold and Kawasaki have figured out that they need such a high oil pump relief valve setting to provide the pressure needed to move the available oil wieght through the passages when cold. The limitations are the conditions under which the bike is likely to be operating combined with the oil which is likely to be chosen. A fact of life is that people don't bother to check and respect the recommended oil viscosity recommendations. If Kawasaki had a problem with KLR650 engines seizing or wearing out camshafts due to thick oil and cold operating conditions, they would receive bad publicity rather than having the blame laid at the feet of the users who behave foolishly.

They have determined that a very high oil pressure relief valve setting (nearly double that of typical automobile pressures) is required to supply the required oil to the top end when people use a heavy oil.

What should we do when selecting oil, according to "Norm"?

Simple, IMO, instead of choosing the heaviest oil available as though we were operating a Harley on the Los Vegas strip, we should consult the recommended oil viscosity recommendations from the bike maker and then use the high number (i.e. use the "40" from the "10W-40" number) as our reference. Choose a "somethingW-40" as the oil rather than a "10W-2,000" as people seem to like to do. Look at the recommended range numbers for the temperature in which we will be operating the bike and choose the lower viscosity base oil so choose 10W-40 rather than 20W-50, or 20W-40. Then, recognize that some oil advances have been made since 1979.

We should, IMO, choose a 5W-40 oil in preference to a 10W-40 if we are using a high end oil such as a synthetic. The "5" will flow more during start-up and get oil to the top end faster than will a "10".

I use 0W-40 in my ST1100 during this time of year because it flows more oil and quicker oil flow.

OK, here's another issue: air cooled versus liquid cooled. Liquid cooled engines tend to have a more stable operating temperature so require less consideration in terms of oil range, correct? Not always.

Put some temperature sensors onto some motorcycle engines and operate the bike and you will learn some very interesting lessons.

Check out some of the KLR650 groups and search for "Bill Watson" and for "Jeff Saline" posts as both have done some extensive work in terms of operating conditions which mirror and expand on much of the work we did in research. I did a couple of thousand posts to the DSN_KLR650 group, some of which relate to these questions.

Hope some of this was useful to someone. Sorry if it sounds "short" and "cranky" but some aspects of technical just hit me that way. Don't mean to offend anyone....just worn down but trying to address the same issues for so long because I see issues affecting many people.

Norm

[robdsuzuki]

Thank you both. Good read. I appreciate it.

[Steve]

Thanks, Norm, well-written.

Goes along with my feelings exactly. Just because you have pressure, does not mean you are lubricating.

Just one thing confuses me, though.

Don't even try that in your garage! (VBG)

Some of us old farts don't do "texting lingo". What the heck is VBG?

.

[robdsuzuki]

I think it means Very Big Grin. rob.

[Steve]

I think it means Very Big Grin. rob.

Well, then, type "Very Big Grin".

If you're too lazy to use all the keys on the keyboard, hit the smiley icon on the right.

If it had come at the end of his well-written post, I could understand that he might have been getting tired, but he still typed a LOT after that, so ...


.

[Rover]

Thanks for taking the time to post this Norm.

[1_v8_merc]

Who cares, it's from the 80's.....it'll run on kool-aid and canola oil.

There's my expert advice!

[FiremanBob]

Thanks for putting up that valuable post, Norm. It would be a great sticky.

[Dogma]

... if we believe that moving parts are actually supported by a pressurized oil cushion as do some people. Silly, but let's keep that in the equation because it actually relates to what is needed but is a misunderstanding.
...

Can you amplify on this one remark?

[Nessism]

For any of you guys worried about using 15W-40 diesel oil now, Suzuki's oil chart (in the service and owners manuals) indicates 15W oil is good down to approximately 7 degrees F, which is damn cold to be riding a motorcycle. In addition to Suzuki allowing this oil, the GS shim and bucket valve train is ultra durable and contains a valve pocket what holds oil for the cam and cam bearings during start up, so even if the oil is slow to reach the cams, there is always a supply of oil waiting there. The 16V engines are more susceptible to top end oiling issues so I'd be more concern with using thick oil if riding one of those bikes, compared to the two valve per cylinder engine bikes. Regardless of Suzuki's allowance though, using an oil like Rotella's 5W-40 is a good idea if you like doing polar bear riding in the frigid cold. I just hope the Suzuki charging system is up to powering that heated riding suit.

[rustybronco]

Take an engine at minus 30 F, using SAE 30 oil and time the interval required from start-up until oil is flowing from the last camshaft bearing onto the lobe.

Sorry but I'm not insane enough to attempt it. although I do have a good friend who works in the dyno lab at Ford. maybe he's tried something similar on one of His RTT* engine tests.

*run 'till termination

[1948man]

Thanks Norm. With your knowledge and your 2 valve 850's forgiving design, your GS should run forever. I've got a couple of gallon jugs of Rotella 5w-40 calling me.

[Normk]

Many people believe that the pressurized oil creates a sort of ring or ballon which supports the rotating component. What actually occurs is that an oil film is maintained between the two surfaces which endures for a period dependent on the film's ability to resist penetration.

Pressure fed connecting rods, for example, fare no better than do splash lubricated in terms of oil film preservation.

When loading is sufficient to expel the oil, the remaining boundary film provided by EP (extreme pressure) additives are compelled to save the day.

Sorry but having to be cryptic because only one hand for typing. Other hand engaged in scratching an insistent small rabbit.

The mention of cold weather riding may bring out some interesting stories. Two old friends used to like to ride (X6 Hustler & torsion spring CB450) around in the snow, especially in following the snow plows.

It will be interesting to see how those 4 stroke, turbo'd snowmobiles fare.

Norm
Norm

Can you amplify on this one remark?