3300 (LG7) Buick Fireball V6 Engine...
I recently acquired a nice old 1993 Olds Ciera S which has a Buick 3.3L V-6 engine. Having run a 1996 Ciera SL until it disintegrated from body rust, I figured the retired Ciera SL would provide a variety of usable spare parts to keep the Ciera S going. There are considerable differences between these two vehicles although a lot of parts are interchangeable.
My first surprise was that the Buick motor explicitly called for 10W-30 API service spec rating SG motor oil. The Ciera SL was not explicit on service rating but called for 5W-30 with the API starburst on the container.
The Ciera SL just had SAE 10W-30 on the oil filler cap but the Ciera S with the Buick 3.3L had SAE 10W-30 and API service SG on the oil filler cap.
Looking in the operators manual, the 3.3L motor was said to be ok with 5W-30 if ambient temperature was below 60 degrees F.
Looking all over the internet, I got the impression that the difference between OW-30, 5W-30, and 10W-30 was quite little. Amsoil claimed that their 5W-30 was 59.5 and 11.7 centistokes at 40 degrees C and 100 degrees C respectively and that their 10W-30 was 66.1 and 11.7.
Thus at operating temperature, both Amsoil oils had the same kinematic viscosity but at lower temperatures the 5W-30 had better flow. I didn't get into the sheer comparisons but they may be a big deal at low temperatures although getting the oil to flow regardless of sheer could beat that argument.
Further reading pointed out that the most recent API rated oils with SN service ratings may not be good for older engines with flat tappet camshafts as opposed to roller cams since the SN rated oils may have less ZDDP anti-scuff additive (zinc dialkyl dithio phosphate) which could lead to cam/lifter scuffing trouble.
Since this Buick 3.3 L motor is standard and with no modifications, I am wondering if going to 5W-30 API SN service rating oil is reasonable since I don't beat the crap out of the car and am a hyper-miler driver attempting to squeeze ever MPG possible out of each fill up?
Any comments or insight would be appreciated. I have never experienced a lubrication related problem on any car I have owned and I drive them to extinction which generally means that the body falls away to the extent that repair of any sort is futile. The engines and non-structural mechanical parts have always gone to the salvage yard in great shape as far as I know.