*ATTENTION SHOPS!* What oil do you use & recommend???
05-12-2011, 08:03 PM
#61
That is true. My engine builder told me to try 20-50 and that if the oil pressure was between 85-100psi at wide open throttle to go down to 10-40. With the turbo and 7k rpms its just under 80psi which means im good. Things get really hot in my engine bay so the oil thins out once its warmed up. At initial start up im between 55-60 at 1krpm...so I have to drive easy(which I do anyways) for at least 10 min until everything warms up.
05-12-2011, 08:37 PM
#62
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Aldo, idk if it has been mentioned but a few people in this thread and throughout the net keep suggesting different initial values... 0-30 and 5-30 refer to the viscosity while the engine is cold and how much oil will flow through a given orifice at a given temperature. Changing to a 0-30 just means more oil will flow faster to the engine during warm up, but that oil will not be as "thick".
Also, the larger a gap between the low and high viscosity the faster an oil will break down and thin out. A 0-40 has a 40 point gap between low and high and is VERY subject to thermal breakdown, whereas a 15-40 not soo much. The basic idea is that the oil will end up somewhere in the middle of the range between the warm/cold temps after a time. This fact is soo true that a lot of people use a strait SAE30 or 40 weight oil and just dont drive till their car is warmed up, helping them guard against thermal breakdown.
As for the relationship between bearing clearances and viscosity, not initial but engine operating temp viscosity. The larger the clearance the thicker the oil you want. It is also related to operating temp in the same way, hotter and thicker. While a larger clearance promotes more engine life, it also has a bad effect on bearing wear while cold. Using too large a gap can cause you to chew up bearings more while the engine is warming up. So you can increase the performance/reliability of your engine by making the clearances slightly larger, but it will require that you warm up your car fully before driving or picking the correct split grade motor oil.
This is only a sampling of why this subject is far too complex to iron it down to which oil is best... to be totally honest even your turbo has a specific oil that may be best for the shaft bearing clearances and that may or may not be the same as your engine. I've blown a turbo bearing by changing the oil to 15-50 from 15-40. So haphazardly guessing at the correct oil for your build based on what someone else used/uses is not the best way to go.
As stated before the basic rule is +10PSI per 1000RPM when warmed up fully. So if you find your PSI below 80 at 7k RPM, you may want to up the viscosity a step until you get the correct pressure. And again, the larger gap between initial and operating temp viscosity the greater the chance of thermal breakdown making that 0w40 actually a SAE20 over time. BEST option for the life of the engine is a straight SAE grade oil with the viscosity needed to keep the pressure/flow up at engine operating conditions. But to do that you would need to let the car warm up every time you use it. Aside from that you want to use the smallest gap between actual and warm up viscosity you can based on where you live and how long it takes for the car to warm up.
Also, the larger a gap between the low and high viscosity the faster an oil will break down and thin out. A 0-40 has a 40 point gap between low and high and is VERY subject to thermal breakdown, whereas a 15-40 not soo much. The basic idea is that the oil will end up somewhere in the middle of the range between the warm/cold temps after a time. This fact is soo true that a lot of people use a strait SAE30 or 40 weight oil and just dont drive till their car is warmed up, helping them guard against thermal breakdown.
As for the relationship between bearing clearances and viscosity, not initial but engine operating temp viscosity. The larger the clearance the thicker the oil you want. It is also related to operating temp in the same way, hotter and thicker. While a larger clearance promotes more engine life, it also has a bad effect on bearing wear while cold. Using too large a gap can cause you to chew up bearings more while the engine is warming up. So you can increase the performance/reliability of your engine by making the clearances slightly larger, but it will require that you warm up your car fully before driving or picking the correct split grade motor oil.
This is only a sampling of why this subject is far too complex to iron it down to which oil is best... to be totally honest even your turbo has a specific oil that may be best for the shaft bearing clearances and that may or may not be the same as your engine. I've blown a turbo bearing by changing the oil to 15-50 from 15-40. So haphazardly guessing at the correct oil for your build based on what someone else used/uses is not the best way to go.
As stated before the basic rule is +10PSI per 1000RPM when warmed up fully. So if you find your PSI below 80 at 7k RPM, you may want to up the viscosity a step until you get the correct pressure. And again, the larger gap between initial and operating temp viscosity the greater the chance of thermal breakdown making that 0w40 actually a SAE20 over time. BEST option for the life of the engine is a straight SAE grade oil with the viscosity needed to keep the pressure/flow up at engine operating conditions. But to do that you would need to let the car warm up every time you use it. Aside from that you want to use the smallest gap between actual and warm up viscosity you can based on where you live and how long it takes for the car to warm up.
Last edited by kingkai; 05-12-2011 at 08:46 PM. Reason: Put something in wrong paragraph
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