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Castrol GTX Classic 20W50 high zinc oil?

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Inkara1 View Drop Down
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    Posted: 04-October-2022 at 5:33AM
My local Walmart now carries Castrol GTX Classic oil that advertises high zinc content (1,400 ppm max). It's available in quart bottles or a 5-quart jug for about $25. Only thing is it only comes in 20W50. Any thoughts on using that weight? The same Walmart carries Motorcraft diesel oil in 10W30 and 10W40 weights. An analysis I found online for the 10W30 says 1,206 ppm of zinc. Thoughts?

Car variables to help with decision: I live in the high desert of California to give an idea of the weather conditions. The engine is a 1972 351C that started as 2V but had the intake swapped to 4V. It has 91K miles, but I don't know the rebuild history if any. I did find a lot of pieces of valve stem seals when I pulled the valve covers. It went through 1.5-2 quarts of oil in a ~250-mile trip, but I don't know how much of that leaked out, how much went through the valve guides, how much if any went past the rings, etc. I don't know what my oil pressure is other than it's enough to turn off the idiot light.
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72 RS 351 Quote  Post ReplyReply Direct Link To This Post Posted: 04-October-2022 at 6:45AM
Finding a suitable old type of oil with the proper amount of zinc etc, for the flat tappet cams and lifters is difficult, and likely they are going away more as time passes. I plan to use a full top brand synthetic, with an additive for my one flat tappet cam 351C. That would be the easiest source for good oil, and keep the cam and lifters healthy. Changing to a roller cam and lifters will eliminate the need for any special old type oils.
Don
73 Ranchero Sport "72 front end", floor shift/console, planning EFI 7000rpm 351-4V &4R70W
73 Ranchero GT 351C-4V 3.70 gears for sale later.
92 Lincoln Mark VII SE, OBDII 347/4R70W
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 72FordGTS Quote  Post ReplyReply Direct Link To This Post Posted: 04-October-2022 at 1:34PM
That's a lot of oil consumption. It might be worthwhile to put a mechanical oil pressure gauge on the engine to see where it is at. 20W50 is way thicker than what these engines should use if healthy. If you want higher zinc for a flat tappet cam, Shell Rotella is a good alternative. You can get it in 10W30 or 15W40. I would think in CA climate and with your oil consumption the 15W40 might be the better option.  
Vince

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Post Options Post Options   Thanks (0) Thanks(0)   Quote aquartlow Quote  Post ReplyReply Direct Link To This Post Posted: 04-October-2022 at 1:56PM
Another "good" alternative for higher zinc content is: Valvoline VR1 Racing 20W-50 Conventional Motor Oil 1 QT - Walmart.com
 
Valvoline VR1 Racing 20W-50 Conventional Motor Oil 1 QT
www.supermotors.net/22468
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 05-October-2022 at 12:32PM
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