This topic has always bothered me. I know the previous owner used conventional Quaker State 10w-30 in my car for years. Based on many recommendations from this site, I started using Valvoline VR1 20w-50, but longed for Mobil 1 since I use it in all my other cars. I wrote Mobil 1 and they provided the following information, which may have confused me more. I purchased Mobil 1 High Mileage 10w-30 synthetic due to the zinc levels and their recommendation, but haven't used it yet. Sorry for the choppiness of the cut and paste. Hopefully it makes sense without my questions included. I'd also love to hear your opinions.
Mobil guys:<<<<For a pre-1980 era engine, one of our criteria is usually to focus on oils with 1000 parts per million of zinc or better, to take good care of a flat tappet camshaft. We've got several oils that fit this profile. One of the most common viscosity recommendations for that time frame is going to be a 10W-30, but a 5W-30 would offer a little better protection during a cold start up.
Everything in the Mobil 1 High Mileage line has been specifically designed with a zinc content of 1100ppm. They are also designed to help clean sludge deposits that might impede flow through small oil passages. Finally, if you're running vintage style seals and gaskets, Mobil 1 High Mileage has seal conditioners that can help prevent leaks.
https://mobiloil.com/en/motor-oils/mobil-1/mobil-1-high-mileageFor most of these motors, for normal street use, we can go with a 30 weight at operating temperature. If you are in a hotter part of the country, I might recommend a 40. Likewise, if you're going to hotrod this car, or have done a rebuild that is little more "aggressive" than stock, we might still lean towards a 40. If we need to handle extra heat, my Mobil 1 Turbo Diesel Truck 5W-40 is a great alternative, with a zinc content of 1250ppm. It's been API rated for gas engines as well as diesel.
https://mobiloil.com/en/motor-oils/mobil-1/mobil-1-turbo-diesel-truck#5W-40 Thank you for choosing Mobil,
If the car runs hot enough for a 50, the Mobil 1 15W-50 is definitely an option. It also has our highest zinc content (1300 ppm) without jumping into a "track use only" racing oil. I have, however, seen cases of customers running a 50 in an engine better suited to a 30, with poor results. If you're not generating enough heat to justify a 50, your engine has to work harder circulating a heavier oil. In extreme cases, you can wind up pumping oil to the top end of the motor faster than it can drain back out. If you try the 15W-50, I would keep an eye out for oil coming out of a valve cover overflow. If that starts to occur, I would recommend stepping back down to a 40.
On the rebuilt engines or those with a new set of heads, we're still going to recommend an elevated zinc level if you're staying with a vintage style flat tappet cam shaft. If a rebuild involves an upgrade to a roller cam, we can look at dialing back the zinc content a little.
Thank you for choosing Mobil, >>>>
