Oil viscosity
 

What viscosity is suggested for older engines, like my 73 450sl with 112,000 miles. I was using 20-50 dino, but a few days ago switched to 5-30 Mobil 1; this is what the mechanic suggested. I've noticed Valvoline markets an oil, non-synthetic, specifically for higher mileage engines (also, they market a similar ATF); does anyone have any experience with these products?

Also, the engine was slightly leaking before the change, and I think its leaking a very little bit more now. I had my heads retourqued today and I'll see how it goes.

There are lots of factors to consider. I run the lightest weight that I can for my local climate, while still maintaining adequate oil pressure. My manual says that .3 bar at idle is acceptable, although I have more pressure than that.

Here is my reasoning:

Heavier oil causes more drag on the rotating assembly, using more gas and robbing power.

Lighter oil flows through the bearings more quickly, carrying away heat and constantly providing cooler, freshly flitered oil to the bearings.

If the oil leak is bad and it bothers you, just fix the leak. I wouldn't play with viscosity to mask over a bad gasket.

BTW, I don't consider your car to be high miles. It's just getting started...

Check the owner's manual for the proper weight. I doubt it will recommend 5W-30. Generally speaking, European cars call for the thick stuff. My neighbor's '91 Audi 100 calls for 15W-40 or 15W-50. For both of my Benzes the owner's manual says a good year-round oil would be 10W-40.