It was 5W-20 when it first appeared. I don't know why they stopped selling that weight other than the difficulty at the time getting anyone to accept a 20 weight oil. 10W-40 oils were very popular then...
[ November 29, 2003, 10:44 PM: Message edited by: jsharp ]
Back in the 1970's many people thought that 10W-40 was like water and a proper oil was 20W-50. A 5W-20 motor oil must have been really tough to sell. It didn't help that the first version of Mobil 1 5W-20 caused major leaks! If I remember the story correctly Mobil 1 5W-20 when it was first released did not have any esters added for seal swell. I believe it was made-up of PAO and a carrie oil for the additives. Latter the formula was changed to a much easier to sell 5W-30 with proper seal swell characteristics that didn't cause leaks.
I imagine that it is very rare to find an original can of Mobil 1 in good condition.
[ November 30, 2003, 01:44 AM: Message edited by: Sin City ]
I understand that a lot of the early synthetics caused a lot of cam failures as well. I know a few older guys that won't touch a synthetic oil because it cost them a lot of money in failures in the past. I think Smokey and Vizard both mention this in some of thier older articals.