Originally Posted By: gfh77665
I noticed you didn't answer why we have multi-vis oils in the first place...
I'll answer that. It's for fuel economy during warm up. It's for easier cranking in extreme cold temperatures in passenger vehicles. It's to protect oil pumps from grenading from excessive internal pressure when some yahoo starts his car with the pedal to the floor mid-winter and bounces it off the redline to heat it up. It's so that manufacturers that sell cars can reduce variences in fuel economy between the short-tripper in Alaska and the 100-mile commuter. Straight weight oil may drag more in extreme cold temperatures, that marginally affects fuel econ for a short time, but the oil film still will not shear like a VII-laden multivis, which is why I believe it offers still better protection, even on cold starts.
Originally Posted By: fsskier
Cold Start/Cold wear: I am suprised so many think that lubrication occurs just because there is oil pressure.
Yes, the bearings have oil. They had oil all night, and receive pressure immediately. The cylinder walls only get what flys off the rod bearings, and the tiny little squirter hold on the top of the rod big end. Rod bearings typically having .002 inch of clearance, nearly no 30 W oil flows through them cold.
You're using older engine designs as an example. Many cars now days have under-piston oil squirters affixed to the bottom of the cylinder, usually fed by a main oil gallery. Even if they rely on holes drilled into the rod big end or passive splashing, then thats just another escape for the cold 30wt to flow through, thus qualifying flow through the bearing. Most engines use pistons with oil holes drilled into the oil control ring groove, allowing yet enough route for oil to transport itself between the cylinderwall and piston skirt. I also don't believe that a cold 30wt would be stagnant in front of so much pressure. What matters is that the film is there, the film is more durable and doesnt need to be replaced through flow as badly as a multivis might need to be. If there is excessive friction at the bearing due to low flow (which still isnt likely), then the heat generated would have the 30wt locally warmed up where it can more easily pass the bearing clearance and be replaced by more shear stable, thick oil for the process to repeat. But we're not talking about slack wax here, I think you may be exaggerating the cold flow characteristics of monogrades.
Quote:
Try loosening up the top of your oil bottle .002 and filling your crankcase with cold oil.
Try generating 60psi, even 5psi in the bottle without it exploding.
Quote:
Similarly MANY seconds elapse between each drop of oil flying off the rod bearing to possibly fly unto the cylinder wall, but more likely flying downward, sideways, or perhaps straight up into the center of the piston.
I don't believe we can reduce the flow to "drops" in the running engine, especially drops so infrequent that seconds pass between them. This is what I mean by 'you may be exaggerating'.
Quote:
Now, imagine that same bearing when hot or thin oil is flowing, a virtual shower of oil flys onto the wall and the piston is hydroplaning with virtually no wear.
that's hydrodynamic loobrikation
Quote:
When GM was switching from 10W40 to 5W30 in the early 80's
they published (in the SAE journal) the results of their multi million dollar lubrication studym they claimed that this change alone would increase engine life nearly 30 percent, assuming a 5 degree F start.
Ford, in an attempt to save money, started not putting the extra drill hole in the rod bearing (big end) from 1974 to 1977. As our older Bitogers know, this resulted in massive failures in the northern states of extreme cylinder wall wear, motors shot by 30-40 k miles. Among my small work group Ford paid for:
two Pinto 2300 CC motors, 1 Maverick 200 Cu in 6 and one Lincoln Continental. Make note that all these engines would have had oil pressure immediately, and the owners that had gauges noticed that they had LESS PRESSURE after the new rods were installed.
PRESSURE IS NOT FLOW!!!!!!
And not every engine is a poorly designed Ford engine from the 70's cranking over in 5*F on 1970's oil! Not to mention, monogrades of today are significantly 'cleaner' compared to the oils of yore. The synthetic monogrades that meet SAE multivis specs are even better!
Quote:
This problem did not occur in the southern states. Now look at the curves above and tell me why we would want such thick oil at colder temperatures??? Then why not run straight 80 W when hot if so much pressure is good and flow is not important??
No one said pressure = flow, although it is a common misconception. When I described cold starting and the time it takes to generate oil pressure, I specifically said "back pressure". Backpressure doesnt indicate flow, but it does indicate the motivation behind the oil.
Engines today have far more efficient oil pumps with higher capacity bypass systems and decently regulated relief pressure. This is why they can run on a variety of oil viscosities with a variety of flow characteristics. On cold engine parts, flow isnt as critical as there is no heat to carry away. If there is heat to carry away, then the oil is no longer cold and viscous. However the quality of the existing film is critical. Monogrades, even when cold will not shear, you know? One viscosity will never be the "fits all" viscosity.
I noticed you didn't answer why we have multi-vis oils in the first place...
I'll answer that. It's for fuel economy during warm up. It's for easier cranking in extreme cold temperatures in passenger vehicles. It's to protect oil pumps from grenading from excessive internal pressure when some yahoo starts his car with the pedal to the floor mid-winter and bounces it off the redline to heat it up. It's so that manufacturers that sell cars can reduce variences in fuel economy between the short-tripper in Alaska and the 100-mile commuter. Straight weight oil may drag more in extreme cold temperatures, that marginally affects fuel econ for a short time, but the oil film still will not shear like a VII-laden multivis, which is why I believe it offers still better protection, even on cold starts.
Originally Posted By: fsskier
Cold Start/Cold wear: I am suprised so many think that lubrication occurs just because there is oil pressure.
Yes, the bearings have oil. They had oil all night, and receive pressure immediately. The cylinder walls only get what flys off the rod bearings, and the tiny little squirter hold on the top of the rod big end. Rod bearings typically having .002 inch of clearance, nearly no 30 W oil flows through them cold.
You're using older engine designs as an example. Many cars now days have under-piston oil squirters affixed to the bottom of the cylinder, usually fed by a main oil gallery. Even if they rely on holes drilled into the rod big end or passive splashing, then thats just another escape for the cold 30wt to flow through, thus qualifying flow through the bearing. Most engines use pistons with oil holes drilled into the oil control ring groove, allowing yet enough route for oil to transport itself between the cylinderwall and piston skirt. I also don't believe that a cold 30wt would be stagnant in front of so much pressure. What matters is that the film is there, the film is more durable and doesnt need to be replaced through flow as badly as a multivis might need to be. If there is excessive friction at the bearing due to low flow (which still isnt likely), then the heat generated would have the 30wt locally warmed up where it can more easily pass the bearing clearance and be replaced by more shear stable, thick oil for the process to repeat. But we're not talking about slack wax here, I think you may be exaggerating the cold flow characteristics of monogrades.
Quote:
Try loosening up the top of your oil bottle .002 and filling your crankcase with cold oil.
Try generating 60psi, even 5psi in the bottle without it exploding.
Quote:
Similarly MANY seconds elapse between each drop of oil flying off the rod bearing to possibly fly unto the cylinder wall, but more likely flying downward, sideways, or perhaps straight up into the center of the piston.
I don't believe we can reduce the flow to "drops" in the running engine, especially drops so infrequent that seconds pass between them. This is what I mean by 'you may be exaggerating'.
Quote:
Now, imagine that same bearing when hot or thin oil is flowing, a virtual shower of oil flys onto the wall and the piston is hydroplaning with virtually no wear.
that's hydrodynamic loobrikation
Quote:
When GM was switching from 10W40 to 5W30 in the early 80's
they published (in the SAE journal) the results of their multi million dollar lubrication studym they claimed that this change alone would increase engine life nearly 30 percent, assuming a 5 degree F start.
Ford, in an attempt to save money, started not putting the extra drill hole in the rod bearing (big end) from 1974 to 1977. As our older Bitogers know, this resulted in massive failures in the northern states of extreme cylinder wall wear, motors shot by 30-40 k miles. Among my small work group Ford paid for:
two Pinto 2300 CC motors, 1 Maverick 200 Cu in 6 and one Lincoln Continental. Make note that all these engines would have had oil pressure immediately, and the owners that had gauges noticed that they had LESS PRESSURE after the new rods were installed.
PRESSURE IS NOT FLOW!!!!!!
And not every engine is a poorly designed Ford engine from the 70's cranking over in 5*F on 1970's oil! Not to mention, monogrades of today are significantly 'cleaner' compared to the oils of yore. The synthetic monogrades that meet SAE multivis specs are even better!
Quote:
This problem did not occur in the southern states. Now look at the curves above and tell me why we would want such thick oil at colder temperatures??? Then why not run straight 80 W when hot if so much pressure is good and flow is not important??
No one said pressure = flow, although it is a common misconception. When I described cold starting and the time it takes to generate oil pressure, I specifically said "back pressure". Backpressure doesnt indicate flow, but it does indicate the motivation behind the oil.
Engines today have far more efficient oil pumps with higher capacity bypass systems and decently regulated relief pressure. This is why they can run on a variety of oil viscosities with a variety of flow characteristics. On cold engine parts, flow isnt as critical as there is no heat to carry away. If there is heat to carry away, then the oil is no longer cold and viscous. However the quality of the existing film is critical. Monogrades, even when cold will not shear, you know? One viscosity will never be the "fits all" viscosity.
