Here we go.............
Thick is better
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Despite beating this topic to death I still find this interesting. Silicon is pretty much the only item on the analyses that is consistent with high wear metals.
I'm not gonna make it.........
from this discussion of viscosity, velocity and operating temperature on hydrodynamic lubrication
Any increase in viscosity results in increased operating temperatures, thus reducing the viscosity, and tends to have a neutral affect on film thickness.
Thicker may be better, given the same contamination level *AND* velocity *AND* operating temperature. Those are big ANDs.
See the guy with the Ferrari running 20W oil, seeing lower operating temperatures, which results in thicker film thickness (all other things being equal... the bulk temp might be lower, but localized temps may be higher in spots, which would be my concern, but if UOAs show good wear metal levels, then he wins!).
Any increase in viscosity results in increased operating temperatures, thus reducing the viscosity, and tends to have a neutral affect on film thickness.
Thicker may be better, given the same contamination level *AND* velocity *AND* operating temperature. Those are big ANDs.
See the guy with the Ferrari running 20W oil, seeing lower operating temperatures, which results in thicker film thickness (all other things being equal... the bulk temp might be lower, but localized temps may be higher in spots, which would be my concern, but if UOAs show good wear metal levels, then he wins!).
Don't miss quote the article.
"Thus an increase in viscosity tends to neutralize itself somewhat."
You can't definitely imply from the article that higher viscosity will automatically neutralize itself completely from the higher operating temp.
Well, I READ about the guy who has the Ferrari,and his claim about lower temps, but, you know something.....I have a sneaking suspicion that the Maranello engine guys spec'ed the oil they do for a reason. IMO there is more to an engine/lubricant system than just sump temps and wear metals in the oil.
tall paul try this link http://members.rennlist.com/oil/Motor Oil 101.htm it should cover the "and" bases too!
Did you see how fuel diluted his Ferari's oil sample was? It could be a ring sealing issue? The milage was also rather low on the sample and it is a hand built engine useing raceing technology and design. If I remember correctly it the sample did not have any track time on it either it was all around town driveing. It is really hard to coralaate the data for it as well as we have not seen any other UOA on his vechile running the approved viscosity. We also have not seen enough UOA on his engine type to really see if their is a patern or trend etc......Last I checked most engines use much lesser material, are mass produced, and do not have a power density any where near his Ferari.
It sounds like the problem is where is the "sweet spot" for thickness. If you're at a normal operating temp of around 100ºC, it sounds like it would be a 30 weight oil. If the temps stray well beyond that, a 40 or 50 weight oil will thin out to that "sweet spot".
How much would an oil cooler (oil to coolant heat exchanger) make a difference? As far as I can tell, their primary duty is to keep the oil temps from straying too far from coolant temps.
How much would an oil cooler (oil to coolant heat exchanger) make a difference? As far as I can tell, their primary duty is to keep the oil temps from straying too far from coolant temps.
This was also posted in the interesting articles ...
http://www.erc.wisc.edu/publications/thesis/thesis/thesis_Dembroski.html
Dembroski, Terry Joseph - MS
Piston Heat Transfer in An air-cooled Engine
Thermal energy flow within the piston of an air-cooled engine was investigated by measuring the heat flux in the engine cylinder liner in the region of travel of the piston rings. Engine sump oil temperature and oil viscosity were varied to change the piston ring heat flow by altering the oil film between the cylinder wall and piston ring. Engine load was varied to change heat flow into the piston. Also, the crankcase oil splash cooling of the piston was varied to change heat flow leaving the piston.
When sump oil temperature was reduced, more heat flowed to the cooler sump. Change in oil viscosity had little effect on the cylinder wall heat flow but increased cylinder wall temperature due to an increase in frictional heating with lower oil viscosity. It was thus determined that this change in heat flow was due to the change in sump oil temperature and was not due to a change in oil film characteristics.
A decrease in engine load decreased the average temperature and heat flux in the cylinder wall. The largest decrease in heat flux was on the exhaust side of the engine where the largest fraction of cylinder heat is convected to the external airflow. It was found that the change in heat flux caused by the decrease in engine load was likely due to a change in the piston ring pack heat flow.
For changes in the crankcase oil splash cooling of the piston, there were only small changes in average temperature and no changes in the heat flux. Although the piston was still believed to lose heat to the crankcase oil splash, its percentage of piston heat loss was too small to affect piston ring pack heat flow.
Superposition was evaluated for sump oil temperature and engine load as well as sump oil temperature and oil viscosity. In both cases, significant error was found with the linear superposition assumption. Linear superposition was assumed not to hold for these complex heat flows.
http://www.erc.wisc.edu/publications/thesis/thesis/thesis_Dembroski.html
Dembroski, Terry Joseph - MS
Piston Heat Transfer in An air-cooled Engine
Thermal energy flow within the piston of an air-cooled engine was investigated by measuring the heat flux in the engine cylinder liner in the region of travel of the piston rings. Engine sump oil temperature and oil viscosity were varied to change the piston ring heat flow by altering the oil film between the cylinder wall and piston ring. Engine load was varied to change heat flow into the piston. Also, the crankcase oil splash cooling of the piston was varied to change heat flow leaving the piston.
When sump oil temperature was reduced, more heat flowed to the cooler sump. Change in oil viscosity had little effect on the cylinder wall heat flow but increased cylinder wall temperature due to an increase in frictional heating with lower oil viscosity. It was thus determined that this change in heat flow was due to the change in sump oil temperature and was not due to a change in oil film characteristics.
A decrease in engine load decreased the average temperature and heat flux in the cylinder wall. The largest decrease in heat flux was on the exhaust side of the engine where the largest fraction of cylinder heat is convected to the external airflow. It was found that the change in heat flux caused by the decrease in engine load was likely due to a change in the piston ring pack heat flow.
For changes in the crankcase oil splash cooling of the piston, there were only small changes in average temperature and no changes in the heat flux. Although the piston was still believed to lose heat to the crankcase oil splash, its percentage of piston heat loss was too small to affect piston ring pack heat flow.
Superposition was evaluated for sump oil temperature and engine load as well as sump oil temperature and oil viscosity. In both cases, significant error was found with the linear superposition assumption. Linear superposition was assumed not to hold for these complex heat flows.
If friction is what creates more heat on the cylinder wall (duh I guess :^) then as others have stated all along you need to look at more than just viscosity, as friction modifiers, oil base, etc. will also have an impact on friction, heat, and assumed wear.
With marginal lubrication an oil with a heavy anti-wear additive level will probably tend to do better than others, which I guess is why HDEOs seem to do so well, syntheic or dino.
With marginal lubrication an oil with a heavy anti-wear additive level will probably tend to do better than others, which I guess is why HDEOs seem to do so well, syntheic or dino.
I might note that one can increase the viscocity of an oil by using it at a lower temperature!
The weight of the oil is not a direct indicator of the viscocity of an oil! However, weight, viscocity index, and temperature can be used to compute the actual viscocity!
TallPaul,you may be right here,to an extent.
It is most likely that an engine with high miles will have some oil dilution due to wear,even though the oil level may seem to be constant.
The constant oil level may be due to fuel in the oil.
A high mileage engine may run well and not show any evidence of smoke but there may be some.
A high mileage engine will most likely have wear,while the wear may still be withing the limits that are acceptable,there is still wear.
This wear may effect different engines in different ways,even the same kind of engine may be affected in differnt ways.
A thicker oil will help to counter any oil dilution and will also help to fill any voids that may be caused by normal wear and tear in an engine.
So,thicker or higher viscosity may be a good thing,especially in an older well kept engine.
It is most likely that an engine with high miles will have some oil dilution due to wear,even though the oil level may seem to be constant.
The constant oil level may be due to fuel in the oil.
A high mileage engine may run well and not show any evidence of smoke but there may be some.
A high mileage engine will most likely have wear,while the wear may still be withing the limits that are acceptable,there is still wear.
This wear may effect different engines in different ways,even the same kind of engine may be affected in differnt ways.
A thicker oil will help to counter any oil dilution and will also help to fill any voids that may be caused by normal wear and tear in an engine.
So,thicker or higher viscosity may be a good thing,especially in an older well kept engine.
You said it yourself... never saw track time... only driven around town... I am guessing (yes, guessing) that that engine rarely was brought up to operating temperature while driving. You could be running D1 and still get high fuel dilution under similar circumstances.
And yes, we don't know what UOAs with approved oil weights in that engine will return... yet. But you have to admit, that guy has big'uns for taking a leap of faith and running 20W oil in that engine! And we're learning from his experimentation, always a plus in my book.
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