ok I haven't been here in a while. but I'm back for a minute.
I went to an auction a few weeks ago, and among one of the lots I bought were a dozen bottles of unopened 10w40. I run that weight oil in all of my vehicles (newest/ 99 Dakota, 3.9, just bought 2 weeks ago) otherwise I have a 96 Dakota/ 318 and 78 Plymouth Sport Fury 318 (this one just turned 54k original miles) so I bought the lot. 6 quarts of Valvoline, the other 6 were Pennzoil.
I was needing to go buy some oil anyways, and it was cheaper than buying 1 qt at the gas station for all 12 quarts.
I put 5 qts (Valvoline) in the 99 Dakota (1st oil change under my watch) and 5 qts Pennzoil in the Fury. The oil looked fine, no separation, anything like that. The Fury has been parked for a year and 1/2, been started and warmed up a handful of times in that span, been driving the snot out of it lately 70 miles a day (hit a deer with the 99 last week, had to order parts and had to get to work) That car is 3 years on its last oil change, probably 2500 miles max. (yeah I know, bad move) Its been in a garage for the offseasons, has hardly been wet since I have owned it. I bought the car 12 years ago with 38k orig miles on it, I am 2nd owner.
Anyways as I was pouring the Pennzoil into the Fury I noticed an auxiliary smaller label on the bottles; 3 of them offered a chance to win a brand new 1989 Cadillac. the other 2 bottles said to enter to win a brand new 1987 Wrangler... Yikes, I knew it was old but not THAT old. Now that the 99 is back together, the Fury will again go to being a "weekend car".
What harm can I do to it by running that oil in it for the rest of this season? I don't anticipate putting more than ~1000 more miles on it before it will again be parked for the winter.