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Oil Viscosity and Grades


Weegie
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Just a short note I'll update the thread later with some more detail hopefully.

Perhaps this is known by many but it wasn't to me until I actually started to look at the data

My HiCam runs hot, to up my pressure I've installed a Griso spring in the Relief valve as the original tends to partially open and rob the system of pressure. This is a big improvement but because the engine easily overheats in traffic and tends to run pretty hot in free air, around 105-110 (I still need to double check these figures), when in traffic it'll drop pressure at idle with temps around 120-130C and 5-10psi, which brings on the oil pressure warn and is a tad toasty anyway.

The downside of the Griso spring is high starting pressure, 85psi idle and I need to wait until 60-65C where the pressure drops quite a bit, I think due to the cooler coming into play. This gives higher RPM, 3k and above, in the 80s.

To counter this I thought go from my 15/50 oil to a 10/60, lower cold pressure and higher running pressure right? That isn't the case when you look at the data sheets, using a couple of Motul spec sheets for a 15/50 and a 10/60, the oil pressure at 40C with the 10/60 is higher by quite a bit at 160 CSt vs 115.7CSt for the 15/50.

Using a far from accurate viscosity estimator based on Walther's equation (really only applicable for Newtonian fluids and mineral oils) I'm roughly estimating that the 10/60 will, more or less, give an equivalent pressure at 10-15C lower temp than the 15/50. So if my pressure X at temp Y running the 15/50 with the 10/60 the pressure X will now be at temp X-10.

Pie in the sky right now as I know the equation isn't accurate, especially if it's extrapolated or even interpolated with large deviations from the actual measured data given by the spec sheet. So it will be interesting to try a 10/60 to see what the pressures actually are, if they are too high I can drop a shim out the PRV.

From the running data and pressures I have already the cold pressures hopefully won't be a problem as looking at a 10C difference when the engine's cold, only moves the pressure around 2 psi or so, prior to the cooler chiming in. When it's hot though it makes a far larger difference as the pressure drops off a cliff using the 15/50 when temp gets between 110-120C. If the 10/60 would hold it to an equivalent engine temp of 100-110 then it might solve the problem.

The effect the 10/60 will have on the engine cooling is a total unknown.

One more thing is my currrent 15/50 at 40C is less viscous than a 10/50 due to the lower viscosity index. The point being don't assume because the Winter number is lower the oil will necessarily be thinner at cold temps that typically a bike is started at, I'm thinking 15C and above as a rule for us fair weather wimps, you really need to look at the viscosity numbers.

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20W/50 @paulnaz, that said remember when it was made most of the more exotic multigrades were not not available and the more modern engines have a 10/60 as the recommended grade.

There are also quite a few HiCam owners running the 10/60 as well to boost pressure at higher temps.

The HiCams are strange, some people have engines that run cold and others toasty hot and nobody AFAIK has any idea why (I certainly don't)

John

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Some live in cold areas, some live in hot.  Some open the throttle, some do not.

 

 

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1 hour ago, 68C said:

Some live in cold areas, some live in hot.  Some open the throttle, some do not.

 

 

Some live in cold areas,

some live in hot. 

Some open the throttle,

some do not.

Is there a second verse? :whistle::sun:

 

 

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    37 minutes ago, Chuck said:

    Oil oil oil

    Can't do with out it

    Oil oil oil

    It's misunderstood...

     

     

    Back to you, Docc.. :rasta:

    Oil oil oil

    Can't do with out it

    Oil oil oil

    It's misunderstood...

    Pretty sure that is actually the chorus . . . ;)

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    10 minutes ago, Chuck said:

    Well, yeah.. I did get ahead a bit.

    The bassman is not allowed to do that . . . .  B)

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    All I know is that I wanted a Royal Oilyfield, aka Oily Enfield 750 Interceptor (chrome tank) in 1970. Having never purchased one, I stand acquitted of any contribution to the 1973 oil crisis. 

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    13 hours ago, 68C said:

    Some live in cold areas, some live in hot.  Some open the throttle, some do not.

     

     

    Realize you're joking but that's not necessarily the case. Phil told me about a guy in Germany who actually blocked off his cooler because the bike ran too cold and Germany has, if anything higher summer temps than here in not so balmy Jockland. Other guys in the US run Centauros at ambients that would cook my engine and yet don't seem to have a problem.

    Another point is that above 3k RPM my 1100 Sporti and the HiCam don't appear to make significantly higher pressures. Why I don't know, logic tells you pressure should rise with RPM but after 3k or so it doesn't appear to increase significantly. It isn't always the PRV coming into play at high temps when the overall pressure is lower increasing the revs above 3k doesn't make any great difference to the oil pressure. I've yet to wring its neck to 8k, but between 3 and 5k I only see 2-3 psi difference.

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    I assume that is because oil pumps don't pump pressure, they pump flow. It is only resistance to that flow that creates pressure. With no resistance to flow there is no pressure. At higher rpms the resistance to oil flow likely goes down, while flow is going up at the same rate, due to increased motion of the various internal parts like the crank and rods.

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    6 minutes ago, GuzziMoto said:

    I assume that is because oil pumps don't pump pressure, they pump flow. It is only resistance to that flow that creates pressure. With no resistance to flow there is no pressure. At higher rpms the resistance to oil flow likely goes down, while flow is going up at the same rate, due to increased motion of the various internal parts like the crank and rods.

    Great explanation..............the oil pump is a positive displacement pump and any pump will produce will produce either pressure, flow or a mixture of both dependent on conditions downstream of the pump.

    I was stuck in the belief that the downstream restrictions were fixed but I suppose their not dependent on leak off from the components, which will rise with RPM, the leakge rate or restriction must alter at approximately the same rate as the pump flowrate rises holding pressure more or less at a fixed value.

    Thanks for that :thumbsup:

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