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Great data - though you should probably note the bike you were using for standards and testing as the smallblocks and CARCs differ in certain recommendations and, I'm assuming may therefore differ on internal operating conditions.Of course, I think smallblock recs vary too by model/year.EDIT - ok, I pulled up some data that might help clarify.CARC, 2TB smallblock Breva 750/Nevada,V7C/R, 1TB Smallblock (I, II, and III), V9, V85, Cali 1100 (hydro and flat tappet) and Cali 1400:Engine Oil: all spec 10/60 (except hydro Cali 1100 which was 5/40, and flat tappet Cali 1100 could also use 20-50) 10/60 is the same as my carc but guess they realised the hydraulic tappets only work well with thinner 5/40 oil at least in first few minutes. So they decided to sacrifice some protection for a quiet bike that customers don't take back to the workshop claiming it's noisy!Transmission Oil (Gearbox in MG speak):* 80/90 - 2TB smallblock (Breva/Nevada, and presumably V7C/R), and Cali 1100 I can see small blocks not needing quite as heavy oil but not sure why Cali 1100 wouldn't unless they're logic is it's not driven as hard, ie on freeway at 55mph lol...?* 85/90 (GL-5) - CARC (B11 shop manual and 2006 Tech bulletin), V7 Mk I, and Cali 1400 I guess for v7 mk1 they just played safe before deciding on 80W90 later??* 75/90 (GL-5) - V7 III (and presumably II, I don't have a manual), V9 I think lower power, higher internal gear speed => thinner oil is ok* 75/140 (GL-5) - V85 I would say that this style of bike might be doing anything from pottering to the shops to very high load / high temp off roading. To cover all possibilities without need to suggest multiple specs they just filled it with a modern very wide multigrade for simplicity (it's not as expensive as it once was either)* 85/140 - CARC (B11 owner's manual) - presumably this is wrong, superseded by 2006 Tech Bulletin Yep that seems to be the caseFinal Drive Oil (Transmission in MG speak):* 80/90 (GL-4) - CARC (B11 workshop manual), Cali 1100 and Cali 1400* 85/140 (GL-4 or GL-5) - CARC (B11 owner's manual but presumably wrong per tech bulletin), 2TB smallblock (Breva 750/Nevada/V7C/R [presumably]), 1TB smallblock (V7 I, II [presumably], and III, V9) This one's more of a puzzle: yes breva spec is wrong, but why would a small block need heavier oil here... are the gears a larger pitch (coarser) perhaps? Whatever it is I would assume they're running a bit hotter than the CARC bikes do.* 75/140 (GL-5) - V85 See v85 point above: grade for very wide range of expected usesNOTE: I'm personally too removed from the CARCs now. I haven't had one in more than half a decade and I only have old tech data on the B11 so maybe someone could check/correct what I've posted here for that. I also found a discrepancy in the little information I actually have (Workshop vs Owner's manual contradict each other). Hell both of those publications are old enough that they actually have the engine oil a 5-40 and not the 10-60 to which the tech bulletin later updated the recommendation.EDIT to EDIT - OK, I added the tech bulletin stuff too.
Hi Kev. Thanks for the extra info, very interesting (to a madman like me), I have added my model now. Also, see my guesses at what the differences below mean. Cheers
My CARC Oil (2009 Stelvio) has never got any hotter than around 40°C/104°F (I have a Temp Sensor in the Fill/Level Plug).That was in ambient temps of around 24°C/75°F, and riding fairly 'briskly'.I'll move the Sensor to the Gearbox at some point soon, just out of curiosity.
Engine Oil: all spec 10/60 (except hydro Cali 1100 which was 5/40, and flat tappet Cali 1100 could also use 20-50) 10/60 is the same as my carc but guess they realised the hydraulic tappets only work well with thinner 5/40 oil at least in first few minutes. So they decided to sacrifice some protection for a quiet bike that customers don't take back to the workshop claiming it's noisy!If you're not familiar with the hydro debacle they had multiple recalls as the camshafts and lifters failed. I can't begin to guess at their logic, I just know the last recall seemed to do the trick, but by then the concept had such a black eye they gave up and went back to flat tappets (and eventually experience new failures with them a decade later on the 8Vs before going to roller rockers).
As far as the engine is concerned, the older bikes quote a 20/50 I'm running a 15/50 full synth in an LM 1000, Sport 1100 and a HiCam engine. The difference in oil temp and pressures in these bikes is markedly different. The HiCam is the problem child and runs in clear air 20C ambient, around 110C, sump temp and overheats in traffic PDQ, pressure also starts to drop through the floor. When I say overheat sump temps 120-130C. I'm upping to a 10/60, as many who run HiCams do and overfill the sump by around 10-15 mm above the max level, but that's another story. IMHO factory specs are to be used where no data exists to prove otherwise, but shouldn't be regarded as set in stone, if you've got data that suggests a possibly better alternateThanks for the information though it's nice to see somebody take a step by step logical approach to the issue and narrow down alternatives in a logical manner, appreciate the data
I've got a point to make, so bear with me while I go over some things. Oil varies in viscosity with temperature- the hotter the oil, the lower the viscosity. But it's important to note that this change is not linear with temperature.The red curve below shows viscosity vs temperature for 10W60 engine oil, and gear oil has the same hyperbolic curve. It isn't hyperbolic but exponential gives a reasonable fit. So what I did was plot a straight line between data points on a *log plot*, hence my interpolations are on an exponential plot- so no, they are not linear. See here for log-linear viscosity plot and how it is fairly straight (i.e. exponential) from 40 to 100 C https://www.engineeringtoolbox.com/dynamic-viscosity-motor-oils-d_1759.html The second point I want to make is that the operating temperature of the engine, transmission and rear wheel drive varies directly with the daily ambient temperature. In other words, if your engine's operating temperature is 90C today at an ambient 20C, the engine temperature will be 95C when the temperature hits 25C tomorrow . Same story for the transmission and rear wheel drive. Hmmmm, I need to do a bit of thermodynamics on that 😊 I think you’re right according to convective heat formula (heat energy proportional to change in temp of object and air flow) but I think it may be more complex than that… will have a think! But yes on first though it seems my 45 deg C shaft in ambient temp of 20 may run at 65 deg C in ambient temp of 40 deg C... not 100% sure tbh Now, let's look at the right portion of the red curve. This part of the curve looks almost flat, doesn't it? This shows that the viscosity at about 100C doesn't vary much with a change in temperature. So for an engine at operating temperature, a change in ambient temperature is not going to affect the viscosity much. (Yes, the oil will breakdown more quickly at higher temperatures, but that's another discussion.)I've plotted *real* data as an exponential function - it does change viscosity. It looks like it doesn't because you're looking at a linear-linear plot and it's hard to see. As an example, from 90 to 100 C the viscosity of high quality Motul fully synth 10W60 changes from about 30 to 20 mm/s^2 (this will be more for mineral). That's not bad or wrong or something to worry about, it's just interesting... You think 10 mm/s^2 change in viscosity is a smaller value compared to the change at the cooler end. And you're right. But as a percentage change in viscosity it is quite large, i.e. decrease of 33% from 90 to 90100 deg C. If you sit at the lights on tickover for a long time on a hot day and your engine oil gets hotter and hotter with no air flow to take the heat away and the oil light comes on: that's why, lower and lower viscosityBut it's a different story for the left side of the graph. Viscosity varies wildly at cooler temps. Note how the graph shows a viscosity of 450 at 20C (room temperature.), 275 at 30C, 175 at 40C, about 100 at 50C, and 75 at 60C! These are all "operating temperatures " of the rear wheel drive, depending on the climate and season you are riding in. Even with the owners using the same brand of oil, the rear wheel drive of a Florida Guzzi consistently sees an oil that has a fraction of the viscosity of a rear wheel drive in rainy, cool England. I beg to differ (not done full calculations though so happy to be persuaded!). I reckon the oil operating temp after say 20 miles of riding will be similar whether ambient temp of 5 deg or 40 deg C (typical extremes of riding temps). Yes hotter in Florida, cooler in England. But I bet my house a bike ridden at 40 C and one ridden at 0 C will not have 40 C difference in shaft or engine temperature as your logic has it above - that's instinctively wrong but according to simple convection theory it is right... surely is more complicated than that no? BTW, the change only *looks* larger at lower temperature. Do the maths and you'll see it is just a trick of the exponential (approx.) curve - plot it as log-linear and it's much clearer! Conclusion: For the rear wheel drive, oil type is not that critical folks. These rear drives are designed to tolerate a huge variation in oil viscosity. Add moly* and you can use any of the oils mentioned in the OP's list. Remember folks, see the passage I posted from BMW Getrag engineers in the last paragraph of my post regarding their view of replacing 90 with 75W90... if you always ride in cold climate, yes can use 75W if you want, if you usually ride in mild climate just stick to the spec. And if you thrash it is hot climate maybe go more viscous...... i think * Or ensure your choice of oil has moly.
What evidence do we have that if you ride normally and change the oil somewhat regularly, that these viscosity variations make a practical difference?
Interesting thread. And yes, I follow the Owner’s Manual and run the recommended 85-90 oil in the gear box of my V7 smallblock (which is a lot harder to find than 80-90).Here’s my concern with this analysis. The starting premise is that Guzzi makes recommendations in the manual which are the conclusions of deep technical analysis and thus the Baseline Platonic Truth. What possible reason do we have to believe this is some profound truth, given we know that the spec can vary over time, that Guzzi has botched the spec with the hydro debacle, and given that oil companies pay off manufacturers to recommend their products?What evidence do we have that if you ride normally and change the oil somewhat regularly, that these viscosity variations make a practical difference?For most people, there is no practical difference between a gearbox that can last “only” 150,000 miles on the “wrong” oil but 300,000 miles on the “right” oil. Why? Because they junk the bike well before 20,000 miles. I suspect the biggest factor for longevity is probably regular oil changes to remove water contamination and metal shards. And I bet it matters a lot that some people shift smoothly and accelerate smoothly and thus keep their gears happy, whereas other bang on the box and otherwise torture it. I’d certainly be interested in data from, say, a bike rental fleet that showed a real world difference just based on gear oil viscosity differences. Maybe the old moly recommendation is part of that data? But my understanding is that the GL5 spec obviated the need for moly. What would happen to gears that didn’t get the moly treatment? And did any of that have anything to do with viscosity?
Since were are on gear oil.GL4 or 5. Did I read right that a rear drive is specifying GL4? I thought that went away with the Loop 4 speed gearbox?EP (Extreme Pressure) additives? I was reading the manual for my '62 F100 about what oil to use in the gearbox, rear drive and steering box. I had read/heard somewhere that it was 20wt motor oil in the gearbox. I wanted to make sure what it needed. It said to use 90wt gear oil NO EP ADDITIVES or 50wt motor oil in the gearbox and I think rear drive as well. I looked at my jugs of 85/90 GL4 and GL5. GL4 has the EP, the GL5 did not say it on the label. Maybe GL5 has EP additives built into the formula, not an additive?Why would Ford specify NO EP in a 4 speed granny 1st gearbox??Tom
What I do not understand is how Redline MT-90 fully synthetic gear oil can be substituted for motor oil, but I read that somewhere...
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