I rounded up a few references regarding oil at start-up and thin oil usage.
Also, make a note that the collection of oil related articles from this year’s SAE congress will be available as publication SP-1967. Order it. The following are from earlier papers:
From Physical Processes Associated with Low Temperature Mineral Oil Rheology: Why the Gelation Index Is not Necessarily a Relative Measure of Gelation, Webber et al:
A high viscosity may lead to engine failure because of inadequate lubricant supply. One failure mechanism is from air-binding (? related to cavitation?) and another is from limited or low flow. Wax crystal formation and oil thickening occurs at much higher temperatures than gelation. Borderline pumping temperatures are much lower than air binding temperature related engine failures.
(We often look only at the pour point thinking that operation above this is safe. What we see here is that problems occur at temperatures more often encountered.)
Low Temperature Oil Pumpability in Emission Controlled Diesel Engines, Mc Geehan et al:
At 4 F it took 100 seconds to get up to pressure at the camshaft using a 15W-40 oil, 60 seconds for a 10W-30 oil and 40 seconds for a 5W-40 synthetic oil. The others was mineral oils, all were SJ rated. The final pressure was 10 PSI higher for the synthetic, “thinner” oil. The sequence was 500 RPM x 5 sec., then start, then idle at 1,200 RPM. The 15W-40 oil had zero pressure at the camshaft for 90 sec. The oil only took 8 sec. to get pressure into the main oil gallery. (? 1 - 2 sec to show pressure at the oil filter where the sender is usually located). The oil flow deficiency is from oil vortex formation in the pump and gelation.
(If we extrapolate that the oil is half as thick at 40 F then according to some people you should get 1/2 the time lapses as recorded in this study. Also, if the oil is moving this slow (impossible according to the constant volume pump theory) then it would continue to flow this slow and only gradually increase flow as the engine oil temperature increases with operation. Even though the pressure is there we can see the flow must be slow. No flow, no lube.)
Similar data was found in: The effects of Crankcase Oil Viscosity on Engine Friction at Low Temperatures, Cockbill et al.
The Use of Low Viscosity Oils to Improve Fuel Economy in LD Diesel Engines, Bennett et al:
The thinner oils had less friction, better gas mileage. Going from a mineral 5W-20 (7.62, 42, 2.6 - 100 C, 40 C, HTHS) to a synthetic (8.95, 46, 2.7) oil gave 1 percent better gas mileage at a steady state 90 Km/h. There was over a 3 percent improvement over a 10W-30 mineral oil (11.8, 77, 3.4).
Fuel Efficient Lubricant Formulations for Passenger Cars or HD Trucks, Benard et al:
Friction using a 50 wt oil decreased with less engine speed. Boundary lubrication is negligible. This is confirmed by the lack of effectiveness of friction modifiers.
With a 20 wt oil friction decreases with increasing speed. Friction modifiers have an important role. Hydrodynamic lubrication increases with increasing engine speed.
In an additive test, friction was tested using a 10W-30 mineral base oil without friction modifiers. 1 percent molybdenum dithiocarbamate increased friction 0.5 percent in one oil and decreased friction 5 percent in another oil. This is secondary to interaction with other additives in the base oil. When using 0.05 percent molybdenum dithiophosphate the friction decreased 8 percent. There was a 9 percent friction reduction adding 1 percent fatty acid C18 ester. (We see the effects of friction modifiers. It is clear you cannot just mix them together. One must look at the whole package to gain benefit with modifiers. Thicker oils gain little with the addition of friction modifiers. Are thick oils with a lot of modifiers just for marketing?)
Engine Oil Pumpability Study in a HD Diesel Truck Engine, Neveu et al:
This basically was a similar test at 5 F to the first test paper I reviewed, similar results. Additional information was taken. They showed that the oil filter was bypassed with all oils for up to 150 seconds with the thickest 15W-40 oil. This was because of the relief valve opening from excessive oil pressures through the filter, as if the filter was clogged with particulates. (The dirty oil on the bottom of the sump gets picked up first and run through the engine without filtration. I always wondered if oil bypassed the filter on start-up.) They recommended a better SAE test correlation for oils reaching wear prone areas as the upper engine in cool, rather then cold testing. More testing at realistic cool start-up weather needs to be studied.
aehaas
Also, make a note that the collection of oil related articles from this year’s SAE congress will be available as publication SP-1967. Order it. The following are from earlier papers:
From Physical Processes Associated with Low Temperature Mineral Oil Rheology: Why the Gelation Index Is not Necessarily a Relative Measure of Gelation, Webber et al:
A high viscosity may lead to engine failure because of inadequate lubricant supply. One failure mechanism is from air-binding (? related to cavitation?) and another is from limited or low flow. Wax crystal formation and oil thickening occurs at much higher temperatures than gelation. Borderline pumping temperatures are much lower than air binding temperature related engine failures.
(We often look only at the pour point thinking that operation above this is safe. What we see here is that problems occur at temperatures more often encountered.)
Low Temperature Oil Pumpability in Emission Controlled Diesel Engines, Mc Geehan et al:
At 4 F it took 100 seconds to get up to pressure at the camshaft using a 15W-40 oil, 60 seconds for a 10W-30 oil and 40 seconds for a 5W-40 synthetic oil. The others was mineral oils, all were SJ rated. The final pressure was 10 PSI higher for the synthetic, “thinner” oil. The sequence was 500 RPM x 5 sec., then start, then idle at 1,200 RPM. The 15W-40 oil had zero pressure at the camshaft for 90 sec. The oil only took 8 sec. to get pressure into the main oil gallery. (? 1 - 2 sec to show pressure at the oil filter where the sender is usually located). The oil flow deficiency is from oil vortex formation in the pump and gelation.
(If we extrapolate that the oil is half as thick at 40 F then according to some people you should get 1/2 the time lapses as recorded in this study. Also, if the oil is moving this slow (impossible according to the constant volume pump theory) then it would continue to flow this slow and only gradually increase flow as the engine oil temperature increases with operation. Even though the pressure is there we can see the flow must be slow. No flow, no lube.)
Similar data was found in: The effects of Crankcase Oil Viscosity on Engine Friction at Low Temperatures, Cockbill et al.
The Use of Low Viscosity Oils to Improve Fuel Economy in LD Diesel Engines, Bennett et al:
The thinner oils had less friction, better gas mileage. Going from a mineral 5W-20 (7.62, 42, 2.6 - 100 C, 40 C, HTHS) to a synthetic (8.95, 46, 2.7) oil gave 1 percent better gas mileage at a steady state 90 Km/h. There was over a 3 percent improvement over a 10W-30 mineral oil (11.8, 77, 3.4).
Fuel Efficient Lubricant Formulations for Passenger Cars or HD Trucks, Benard et al:
Friction using a 50 wt oil decreased with less engine speed. Boundary lubrication is negligible. This is confirmed by the lack of effectiveness of friction modifiers.
With a 20 wt oil friction decreases with increasing speed. Friction modifiers have an important role. Hydrodynamic lubrication increases with increasing engine speed.
In an additive test, friction was tested using a 10W-30 mineral base oil without friction modifiers. 1 percent molybdenum dithiocarbamate increased friction 0.5 percent in one oil and decreased friction 5 percent in another oil. This is secondary to interaction with other additives in the base oil. When using 0.05 percent molybdenum dithiophosphate the friction decreased 8 percent. There was a 9 percent friction reduction adding 1 percent fatty acid C18 ester. (We see the effects of friction modifiers. It is clear you cannot just mix them together. One must look at the whole package to gain benefit with modifiers. Thicker oils gain little with the addition of friction modifiers. Are thick oils with a lot of modifiers just for marketing?)
Engine Oil Pumpability Study in a HD Diesel Truck Engine, Neveu et al:
This basically was a similar test at 5 F to the first test paper I reviewed, similar results. Additional information was taken. They showed that the oil filter was bypassed with all oils for up to 150 seconds with the thickest 15W-40 oil. This was because of the relief valve opening from excessive oil pressures through the filter, as if the filter was clogged with particulates. (The dirty oil on the bottom of the sump gets picked up first and run through the engine without filtration. I always wondered if oil bypassed the filter on start-up.) They recommended a better SAE test correlation for oils reaching wear prone areas as the upper engine in cool, rather then cold testing. More testing at realistic cool start-up weather needs to be studied.
aehaas
