Proper oil for older engine

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Jul 15, 2022
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Tomball, TX
Hello new member here. Got a new to me 1980 Chevrolet pickup with a 350 V8 and only 44k miles on it. I understand this is a flat tappet engine and the oils in it’s heyday had enough phosphorus to protect the cam. However oils today have significantly less...the practical solution is to use a high zinc oil such as Amsoil 10w40 or Mobil 1 0w40, BUT this truck also has its factory catalytic converter which I don’t want to ruin either. Currently running Mobil 1 extended performance, but I’m worried about that flat tappet cam becoming worn while trying to keep the converter happy.. What do you guys suggest? And no I really don’t want to run that Castrol 20w50 “Classic” oil as a 20w50 is too thick.
 

Chad98

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The sooner you plug up that old pellet style cat and replace it with a free flowing one the better.

I’ve actually done that, was recommended by the muffler shop when I had the flow master exhaust put on
 
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Apple Valley, California
That era Chevy engines either ate cams or they didn't. It was a metallurgy problem no oil will fix. If you are worried that it's burning oil and will poison the cat with a higher zddp oil you don't have much choice but to run what's on the shelf.
 
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I would think that even a modern oil would have enough zinc to keep that stock camshaft happy, but that's my opinion. Having said that, you could try blending 3 qts conventional oil (10w30 or 10w40) with 2 qts HDEO (Diesel rated 10w30, 15w40). That would probably bump the zinc up to 1980 levels.
 
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Motorcycle oils have higher zinc levels, but also have to protect cat converters. Plenty of motorcycle oils available in 10w-30 weight.
 
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Flat tappet 350 truck motor only need extra ZDDP if you have an aftermarket high lift cam and stiff valve springs. Any modern off the shelf oil will be more than fine, generally the only cams you find wiped out on old OHV small blocks happened because the cam wasn't properly induction hardened at the factory and no oil will fix that.
 

FCD

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Have always used the latest API oil in my 60's designed flat tappet tractor engine in my '93 F150. Previous (original) owner did the sane. Modern anti-wear additives has replaced ZDDP.
No they haven't all engine oils still have Zddp for a reason, no real replacement has been found for it, it can be partially replaced by Boron for example, but not entirely.

Although it is true not all flat tappet engines need a huge Zddp level, your tractor or that 93 F150 or OP's truck have relatively mild flat tappet cams, which can probably get by fine with 900-1000ppm.

However if you have a more aggressive cam with more lift / stiff valve springs, an oil with a high Zddp level is still a good idea if you want to be protected against lobe wear.
 
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No they haven't all engine oils still have Zddp for a reason, no real replacement has been found for it, it can be partially replaced by Boron for example, but not entirely.

Although it is true not all flat tappet engines need a huge Zddp level, your tractor or that 93 F150 or OP's truck have relatively mild flat tappet cams, which can probably get by fine with 900-1000ppm.

However if you have a more aggressive cam with more lift / stiff valve springs, an oil with a high Zddp level is still a good idea if you want to be protected against lobe wear.
You see my point?
 

OVERKILL

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Hello new member here. Got a new to me 1980 Chevrolet pickup with a 350 V8 and only 44k miles on it. I understand this is a flat tappet engine and the oils in it’s heyday had enough phosphorus to protect the cam. However oils today have significantly less...the practical solution is to use a high zinc oil such as Amsoil 10w40 or Mobil 1 0w40, BUT this truck also has its factory catalytic converter which I don’t want to ruin either. Currently running Mobil 1 extended performance, but I’m worried about that flat tappet cam becoming worn while trying to keep the converter happy.. What do you guys suggest? And no I really don’t want to run that Castrol 20w50 “Classic” oil as a 20w50 is too thick.
Phosphorous has been all over the map, even back before it was restricted, many oils didn't have high levels, it was a bit of a gamble depending on what you purchased. If you want something with higher levels of AW additives (higher ZDDP) you can't go wrong with a full-SAPS Euro oil like M1 0W-40 which is better than anything that existed when that truck was new.
 
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Rotella T4/5, Valvoline Blue, or Motorcraft (all diesel formulations) 10w30, 15w40 if it burns quite a bit. Those have enough zinc, with more appropriate additives for daily use and cleaning up/keeping the engine clean than "classic" or "racing" oils. Cheaper and, in most places, easier to find as well. I'm currently using Mobil1 0w40 in my '85 big block C30 and am satisfied with it, too. If I can still get it at Walmart prices when it's time for the next oil change, I may run it again and do a UOA out of curiosity.
 

wlk

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I run a 5qt jug of Quaker State High Mileage 10w40 syn blend with a bottle of Schaeffer Moly EP in my 93 C1500 5.7l and it is great. Probably equals a 50 to low 60 weight, did the math once, think is was 15-16ish cst at 100c. but can't remember exactly. Have ran it for a while but will be switching to QSFS 5w40, Walmart sale, w the Moly EP for a while as I bought a bunch of it. I was running 5w30 but was burning oil, now consumption is way down. Once my stash of 5w40 is gone I will go back to the QS HM blend, great oil for the price. Last summer I ran 5w40 Rotella t6 and it was fine too. Run any 5w40/10w40 synthetic or blend and you'll be fine. Mobil has the 10w50 and Castrol GTX HM has a 20w50 which will work too esp if hauling or towing w it.
 
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