I thought I would share my experience with viscosity and synthetic oil brands. I am the second owner of the Lesabre (3.8 Series II) and purchased the car from family friend with only 39k on it. The car has been pampered all its life with the original owner keeping impeccable service records since he is as anal as I am about maintenance. Except for its factory fill, the car has been run on synthetics all its life. GM specifically emphasized in the owners manual that 10w30 was preferred and only indicates trying 5w30 below freezing range of temps. First owner used M 1. I first was using Napa Synthetic (Valvoline essentially) and both of those brands in 10w30 showed virtually no oil consumption over 5k OCIs. When winter came, I thought I would try the 5w30 but that was short lived. On startup, the engine emitted "rattling" sounds and even when warm, the car never sounded quite the same as on the 10w30. Mind you, I have not even heard of BITOG at the time and so I had no built in bias for or against 5w30 oils since my prior car (Honda) thrived on it. This issue with 5w30 happened with Napa Syn and the M1. When I switched over to PP and PPU, I have noted that I even get some oil consumption with that brand's 10w30.
I wonder if part of this issue is due to the relatively "ancient' origins of my engines design. Were tolerances a lot different from engines today? And if so, would that explain why the 3.8 seems to be happier on certain brands of 10w30? I guess I'm wondering if the avg. viscosity of 10w30 oils varies enough to cause what I sense is a lack of oil pressure (from the 5w30 oils) and that even some of my oil loss with 10w30's is due to lower viscosity from some synthetics like the PP? I have decided to try switching over to Castrol 10w30 HM Semi-syn to see how the 3.8 responds to what I hear is higher viscosity range. Has anyone else ever noted oil pressure issues (low) related to viscosity variances amongst oil brands? This car has never been abused and even though I'm not a senior citizen, I drive like one
I wonder if part of this issue is due to the relatively "ancient' origins of my engines design. Were tolerances a lot different from engines today? And if so, would that explain why the 3.8 seems to be happier on certain brands of 10w30? I guess I'm wondering if the avg. viscosity of 10w30 oils varies enough to cause what I sense is a lack of oil pressure (from the 5w30 oils) and that even some of my oil loss with 10w30's is due to lower viscosity from some synthetics like the PP? I have decided to try switching over to Castrol 10w30 HM Semi-syn to see how the 3.8 responds to what I hear is higher viscosity range. Has anyone else ever noted oil pressure issues (low) related to viscosity variances amongst oil brands? This car has never been abused and even though I'm not a senior citizen, I drive like one