Redline 5w20 vs 0w30 almost identical specs

[A_Harman]

Originally Posted By: chicagophil
so, for a car that originally spec'd 10w30 (in '99), with the manufacturer knowing many owners would use dino, it seems either Redline's 5w20 or 0w30 would be a better fit, given the 3.2-3.3 HTHS, than the 3.8 of the 5w30 and 10w30.

regarding this line:
Quote:
RL 5W-20 is heavier than RL's 0W-30 at all temperatures for two reasons; it has a higher HTHS of 3.3cP vs 3.2cP and a very much lower VI of only 145 vs 183 for RL's 0W-30


how significant is each tenth in cP? 3.3 vs 3.2 (vs 3.8)?

what is the implication of the large VI difference?


API specs require an HTHS of at least 2.9 for an oil to qualify as a 30-weight. As long as the oil is above that, it will be good to use where the manufacturer has specified a 30-weight. Higher HTHS is OK, but is directionally wrong if you are concerned about fuel economy. Also, API specs do not have upper limits for HTHS within the various viscosity grades.

 

[CATERHAM]

Originally Posted By: chicagophil
so, for a car that originally spec'd 10w30 (in '99), with the manufacturer knowing many owners would use dino, it seems either Redline's 5w20 or 0w30 would be a better fit, given the 3.2-3.3 HTHS, than the 3.8 of the 5w30 and 10w30.

regarding this line:
Quote:
RL 5W-20 is heavier than RL's 0W-30 at all temperatures for two reasons; it has a higher HTHS of 3.3cP vs 3.2cP and a very much lower VI of only 145 vs 183 for RL's 0W-30


how significant is each tenth in cP? 3.3 vs 3.2 (vs 3.8)?

what is the implication of the large VI difference?

HTHS viscosity correlates very closely with an engine's oil pressure at operating temperature. Each tenth cP will translate into a 3 to 5 psi OP difference. That's one reason why the HTHS vis is sometimes given to two decimal places.

RL's 5W-20 is an old formulation that pre-dates the development of their 0W-XX range of oils. A VI of 145 is very low for a multi-grade synthetic oil. A low VI simply means the oil is very thick when cold. RL 5W-20 is 30% thicker than RL 0W-30 at 32F and more so at lower temp's.

 

[dailydriver]

Originally Posted By: Ben99GT
Originally Posted By: CATERHAM
Ben, I recall you mentioning this before in another RL discussion, and IIRC it was a drag racing situation were the oil temp's are very low, often under 40C.


It was on a 2300+ HP 4.6 4V seeing 40+ lbs of turbocharged boost spinning 10,000 rpm. The timing chain was acting as an oil escalator causing oil to pile up in the right cylinder head. This issue was actually observed on the engine dyno, IIRC.


Yes, as he said, an engine which sees (or will see) low 6 to low 7 seconds of full boost/WOT use at a time, at very low oil temps.
Between the power/cooling gains from the thinner oil, and the 'escalator effect' you've described from using the heavier stuff, the builders would be stupid to use anything thicker for that application (given the proper bearing clearances/OP of course).