In the 70 owners manual there's a recommended oil viscosity chart. This one- Now, the way I read it is, from 20 degrees to 100 degrees and over, the recommended oils are 20w, 10w-30, 10w-40 and 20w-40. All are acceptable for this range of temperature. That's why there are commas. I was showing this to someone and he interpreted it completely different. He claims that as the temperature goes up, buick is recommending the heavier oil. So 10w-30 is not recommended for 100 degree Temps. How do you read this chart?
So from what it seems like the gentleman that you were speaking with sounds absolutely correct and very knowledgeable a I would think he is correct and that's how I also read it
Any way you look at it if you have consistant 80-100+ degrees 20W-40 or even 20W-50 would offer most protection. Talking to a guy at a car show with a nice 70 Electra few years ago and he said he runs 5W-30 all year round but had to turn the idle speed up to keep the oil light from coming on...... Heard a loud knock when he started it like spark knock....didn't ask him what octane he ran.....probably one of those who tries to save a little $$ by running like 89 instead of 93.
While they may all be acceptable for use in that temperature range, that does not mean you can disregard the ambient current temperature. Higher weight oils offer better protection in elevated temperatures, and you can infer that from the chart.
Thank you for reinforcing my point. 10w30 is listed as one of the acceptable oil viscosities. The protection of 10w30 doesn't end at 80 degrees and 20w50 takes over
It seems to me that in a factory configured car, this only really affect the warm up. You need to have oil that doesn't get too thick when cold so that when you start the car it can crank. Once the car reaches normal operating temps, the ambient temp isn't really meaningful? If the cooling system is working well and maintaining the operating temp of the engine at 195 (example), that should be it? I think you read the chart right, although the other gentleman's point isn't wrong either. With synthetic oils the cold start issue isn't as extreme (they don't get as stiff in the cold). I think 10-40 for summer driving seems ideal. (how many actually drive there cars in the cold these days?
No, but if you were living in the southwest where temperatures were consistently near and above triple digits, would you be using 20W, or 20W/40? Now consider what you told me Friday about not being too happy with your hot idle oil pressure. Same scenario, high temperatures, wouldn't you use the thicker oil? That's what the chart tells you to do. The arrow isn't just for temperature, it's for oil viscosity as well. Higher temperatures, higher viscosity.
Again, they listing a range of viscosities you can use for that temperature range. According to the chart, 10w30 is good for 0 degrees up to 100+. Its acceptable. If I were in Arizona, I'd probably run 20w50, yes as the Temps exceed 100 degrees on a regular basis.
Don't forget these motors had 195* thermostats in them if a/c equipt, so they ran at abt 200*. Most of us are now running 180's.
Remember too that most of our cars have lots of miles on them. Looser bearing clearances, weaker ring sealing, half clogged radiators making motor run warmer. So...they will appreciate a little thicker oil when hot. Less leaks too. I told a guy with a leaking rear main to switch from 10-30 to 20-50 and it almost completely stopped leak.
One other thing to mention. Look at the 3 rows in the above diagram. The second row has no arrow at either end. I would interpret that as recommending any of those oils, 10W, 5W-30, 10W-30, and 10W-40 for temperatures between 0*, and 60*. The first row has an arrowhead for temperatures increasing to 100*. The third row has a arrowhead for decreasing temperatures to -30*. The oils listed get thinner in the decreasing temperature direction, and thicker in the increasing temperature direction.
The way I see it that chart is 52 yrs old.... Today oil is totally different than yesteryears oils. So now ( today) I guess I'll not walk a mile for a camel. Reason we should know better.
For the record, every GS I've ever owned, I ran 10w30 with zero issues. If your bearing clearances are right, your timing case cover isn't worn and the pump is set up correctly, you can run 10w30 in 100 degree weather.
I’ve always run 10w40 but I live in the Southeast. I would think 10w30 is perfect for northern climates.
I agree, but you brought this up Friday. You aren't happy with your oil pressure. You have two choices try a thicker oil, or check/replace your timing cover. Maybe try the TA oil pump shim kit first.
I wouldn't put a ton of faith in "today's" oils....alot less antifriction additives (zinc, moly, barium, phosphorus) than "old" oils....due to cat converters not being able to handle them.....new is not always better. Today's engines have anti-friction (roller cam, roller lifters needle bearings, etc) built into them rather than relying on the oil.
Good point, but I don't think that would impact oil pressure. I wonder what oil Jason is using. Probably something with sufficient Zinc, like Valvoline VR-1.
