Hey scotty,
I have a 1986 f150 with a 300 straight six carbureted engine. I know from a few youtubers that do old car revivals that some cars/trucks needed a zinc additive in the oil to protect the "Flat tappet" camshaft. Do i need this additive in this truck oil or is conventional 10w-30 good enough for it?
Also, if the engine is warmed up and idling and the pressure gets down to around 15psi, can i put in conventional 10w-40 or something else to make the idling oil pressure higher? (At cold start it's at 50psi)
There are a lot of opinions on the zinc/ZDDP issue. It certainly can't hurt to use an additive or use a specialty zinc-rich oil. Many say that if the cam is long broken in and the engine is not a high-performance job (that is, it has bog-standard valve springs and does not have a high-lift cam) that it is not necessary, particularly if not subject to heavy-duty use.
So it comes down to a judgement call. For what it's worth I have not done anything special for my older flat-tappet vehicles and not had any problems.
I don't know what the oil pressure spec is for that engine but the general rule of thumb for old-school pushrod engines is a minimum hot pressure of 10 psi per 1000 rpm. What's the oil pressure at speed? You might want to verify the oil pressure with a mechanical gauge if you're using a built-in dash gauge.
Hmm oki i'll take a few tests on the zinc additive, and see what turns out best.
For the oil, the dash guage never worked so i installed an old-school mechanical guage. At cold start idle (i'm guessing 700 rpm i don't have a tach), it shows around 50psi, (reving it, it stays the same), but gradually, when the engine warms up fully, the pressure drops down to around 15psi, but when i rev it or when i'm driving it down the road, the oil guage acts like a tachometer, so when it's at 15psi, and i rev it, it goes up to like 40psi, but when it's idling again it drops down. Is it something i should be worried about?
You could check your pressure against the factory specs but going by the old rule-of-thumb you're in safe territory.