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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 7000+ rpm 351-4V &4R70W
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, 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.  
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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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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 11-June-2023 at 8:19PM
I guess I should update this. My Walmart doesn't have the Castrol classic car oil anymore. [shrug emoji]

I'm currently running 15W40 diesel oil I got at Costco. I did install a pressure gauge, and I'm getting just under 80 psi at cold start, ~20 at warm idle, and ~50 at 70 mph (2600 RPM). I'm not worried about low oil pressure now. I also torqued the oil pan bolts to 11 ft-lbs and that seems to have stopped the dripping there. I even found a "Tite-Reach" chain drive extension for my 1/4-inch-drive sockets so I could tighten the bolts that the crossmember blocks access to.

I also replaced 15 of the 16 unbrella valve seals last night. They were all gone. The only reason I didn't replace all 16 is because I can't get my spring compressor onto the exhaust valve spring on cylinder 4 because the air conditioner box is in the way. I'm debating whether to cut the star wheel off the tool so I can get it on the spring and then see if I can turn it with vice grips or something, or whether to leave it be since it's an exhaust valve instead of intake. Thoughts? Not sure if cutting the star wheel off the tool would even guarantee success.
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 Rockatansky Quote  Post ReplyReply Direct Link To This Post Posted: 12-June-2023 at 3:59PM
would pulling the motor mount bolt out and jacking the engine get you enough angle for the spring compressor to fit?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Inkara1 Quote  Post ReplyReply Direct Link To This Post Posted: 12-June-2023 at 10:51PM
I actually have good news to report for this. I got the star wheel removed, and that extra clearance, combined with the slight bend in the tool my $12 Harbor Freight spring compressor developed in use, meant I could get it to fit on the spring with the shaft the star wheel used to be on just touching the a/c box. Then I used my old robo-grip pliers to turn the screw on the compressor. Now all 16 valves have new seals. Really looking forward to lowering my oil consumption significantly.

Unhooking the passenger-side motor mount and jacking up the engine would have been the next thing to try, but I'm glad I could save that step.
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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