5w-20 again!
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
Originally posted by 2fords2
Why is CF an advantage? I've never paid attention to diesel specs before when picking auto oil.
Why is CF an advantage? I've never paid attention to diesel specs before when picking auto oil.
A little-considered advantage of 5W-20 over 5W-30 dino is the smaller "viscosity spread", meaning that fewer polymers are added to thicken the oil at operating temperature and possibly oxidize or otherwise breakdown. If I were to go thicker in summer, it would be 10W-30 for that reason. The "W" rating is cold-cranking viscosity measured at -20 to -35 degrees C for the different weights. Unfortunately, our trucks do not have oil temperature guages. Coolant and oil temperatures do not necessarily correlate.
Jim
Senior User
Joined: Jan 2001
Posts: 416
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What ever happened to straight weight oils? A 5/20 or 30 weight oil is just a 5 weight oil with a bunch of addatives to make it think it is a 20/30 weight oil but eventually these addatives break down and you end up with dirty 5 weight oil. I use a straight weight 20 in the winter and 30 in the summer and I have 356,000km on the motor now. Straight weight oils will get thinner with age and heat and whatever gasoline that gets by the rings but not as bad as a multi grade oil. And what is with a "0" weight oil! Water is "0" weight for crying out loud. Not much lubrication there I would imagine, in the oil that is.
Post Fiend
Joined: Jun 2001
Posts: 5,228
Likes: 5
From: Running Springs CA
I still use straight weight in air cooled engines because that is what is specified in the manual. 30 for the VW and 50 for the Cessna. Those engines are built with "loose" clearances and do contaminate the oil with a lot of blowby. These engines do not even have oil filters.
Modern EFI car and light truck engines, particularly those with hydraulic lifter overhead cams, are a different animal. Startup oil flow is more important and blowby is minimal.
Modern oil chemistry is also vastly improved from decades ago, allowing for more stable multigrades. Oil analysis has shown that the breakdown is minimal for synthetics and the modern Group II dino's. Straight grades still use Group I chemistry. I still believe that a minimum viscosity "spread" is best for dino, accounting for the operating climate.
Jim
Modern EFI car and light truck engines, particularly those with hydraulic lifter overhead cams, are a different animal. Startup oil flow is more important and blowby is minimal.
Modern oil chemistry is also vastly improved from decades ago, allowing for more stable multigrades. Oil analysis has shown that the breakdown is minimal for synthetics and the modern Group II dino's. Straight grades still use Group I chemistry. I still believe that a minimum viscosity "spread" is best for dino, accounting for the operating climate.
Jim
