Have any of you tried it in an older muscle car engine? Pre 70's cars?

I've got a '73 Cadillac CoupeDeVille I use every day. I've run Mobil 1 15-50 in it during the summer and Mobil 1 10-30EP during the winter for about the last 5 years. I ran the 15-50 year round up until about 5 years ago.

I just changed the oil to the TDT 5-40 for this winter instead of the 10-30EP. It has a higher ZDDP level for old cars and 10-30 EP that had more ZDDP is becoming unavailable. I'll see how it works. I don't do UOA's.

I've been doing a lot of short trip use in the cold weather recently and the 15-50 stank to high heaven when I changed it after only 2500 miles. It NEVER did that with the long trips I used it for most of the 13 years. I'll see what happens with the 5-40. It is low on ZDDP at 1000ppm for older cars but the Caddy motors have notoriously weak valve springs so it shouldn't be a problem.

For an old muscle car? I'd have to wonder about the ZDDP levels of Mobil 1 5-40 TDT. I think they would be way low. I may even add some ZDP to my oil tommorrow.