Any advatages in using original GM 6041-M oil
 

Are there any advantages in using original GM 6041-M spec engine oil in my 71?
I found a company in Germany that produces engine oils for classic cars that conform to original specifications?
Here is the link to manufacturer:
https://www.rektol-klassik.de/produc...C.html&Liter=5

If the engine in your '71 is the original engine, or one that is similar to the original engine, it has what's known as a "flat tappet" camshaft, as opposed to a "roller" camshaft. The interface between the bottoms of the "flat" lifters (tappets), is an area of high friction. The oils originally used in these engines was fortified with a Zinc Phosphorous additive (ZDPP), in order to provide adequate lubrication at the cam/lifter interface. This isn't an issue with newer cars, as most cars manufactured after 1987-88, have had roller camshafts.

A few years ago, the US's environmental protection people decided that this oil additive contributed to the shortening of the useful life of catalytic converters. They also felt that there weren't enough cars on the road any longer, that needed the protection of the ZDPP additive. Personally, I think that's a load of BS, as there are still a LOT of older cars on the road. Nonetheless, they required the American oil suppliers to cut back/eliminate on the amount of ZDPP they put in the motor oils of today. While that will be more or less OK for current engines, it is definitely NOT OK for older engines. The lack of the zinc additive will drastically shorten the life of your camshaft, as well as circulate all of that ground up metal through your engine.

The short answer is that you should use a gasoline oil with the proper amount of ZDDP additive. There are many gasoline oils sold here that have the proper amount of ZDDP. I would use one of them and skip buying one from Germany.

Thanks! I live in Europe and buying from Germany is easy and shipping is like $15! Amsoil z-rod is twice the price!

Two separate responses to your question.
1) I do not, and no one who has yet responded has any real knowledge of the properties of motor oils required in the EU and can only provide an opinion.
2) Having said that, there has been a great deal of progress (most of it very beneficial - see discussion of zinc phosphate above for a minus) made in the last 40-50 years (since 1971). I suggest you take advantage of this progress, and use a modern oil with the requisite amount of zinc phosphate. Unless your engine is on the ragged edge of needing a rebuild (new gaskets and seals, etc) it will cause your engine no harm and may help with reduced friction/wear.

FWIW - continue to use the viscosity recommended. Also, some owners recommend against synthetic oils in higher mileage engines - they claim it penetrates into very small spaces and causes oil leaks (Many others have not experienced this). I would be on the safe side and continue to use petroleum derived oils.

Use 10w-30 as per owners manual? Although the owners manual suggest using other viscosity for higher or lower temperature climates.
I like to use 10w-40 as in the summer it gets quite hot wherre I live.

Short answer is "No." Modern oils are much better than what was specified 40 years ago. And counter to most folks perspective, full synthetic oils are SO MUCH better at minimizing wear and maximizing engine life, we would be fools not to use them. That said, most full synthetics do not come with enough zinc for high performance solid lifter, flat-tappet cam engines, so you would need some additive. But, if you have a stock hydraulic lifter engine and don't run the poop out of it all the time, full synthetics off the shelf are perfectly fine.

P.S. More leaks occur when you switch to full synthetic oils because the molecular size of synthetic oil is much smaller than for organic oils. If the seals are worn enough, synthetics will leak sooner. But, it's just letting you know that the seals are worn and need to be replaced.