Hi All, I've searched to try to find this here, and I bet it is, but i just cant find it. SO....
At start up and cool engine, I get about 30 psi. When I get it up around 2500 rpm, I get about 50psi. But after I drive for a while( maybe 25 minutes) when I come to a stoplight, I drop to about 5-10 psi at 850-ish rpm. I get back up to 40-50 when I accelerate hard again to 2500. That feels scary to me, but is that normal? Fresh oil, new filter.
'68 400HO Coupe, 4 spd, 259 interior, Windward Blue. My other car's a Johnson 15 outboard on a '61 Starcraft rowboat... Just sayin'.
Pontiac recommended that the HO engines use straight 30W in the summer.
Summer '69 Mr. Goodwrench pointed out that footnote in my '68 Owner's Manual when I told them I was using 10W30 during a warranty visit. After 51 years, I cannot remember if the Service Manager underlined that in the book or if I did.
That’s real similar to what my 68 400 HO’s oil pressure runs. After mine was good and hot it would drop to about 10psi maybe even a hair less when idling around that 800-850 rpm, I adjusted the idle so it’s up around like 900-950 rpm and just that little extra keeps it up around 15psi. I’ve always run Driven HR 10w-30 and the last oil change I decided to try the Driven HR 10w-40 and I actually might switch back to the 10w-30. For the first 10-15 min with the 40w it actually gets up around like 75-80psi if you get the rpms up there, once it’s good and hot it settles in at about 60-65psi at cruising speed and about 20psi idling around that 900 rpm range.
I was always told an old stand by is 10psi for every 1000 rpm, if that’s the case 10psi should be plenty idling at 850 psi.🤷🏼♂️
"Pontiac recommended that the HO engines use straight 30W in the summer." MEANING WHAT... 0W-30?
sorry about the caps...
Not sure I understand your comment but this is what I've used for decades in my 400HO, straight 30W as noted in the Owner's Manual, not a multiviscosity oil: (Plus, now I add 4 oz of ZDDP to replace the zinc that has been removed from the oil of the 60's-80's)
I wouldn’t worry about it too much if I were you. My first car was a 1982 firebird, and when warmed up its oil pressure was less than five pounds. I worried quite a bit when I discovered this, but I ultimately drove it another 50,000 miles before I sold it. The car still ran great. The oil pressure situation never gave me any problems. It was still getting oil—albeit not as much as I would have preferred.
When there are two numbers it is multi viscosity oil. It has an additive so that when it heats up it acts like a higher viscosity oil. Something about cross linking of the polymer chains that increases the viscosity when it heats up. So 10W-30 acts like a 10 weight oil when cold but a 30 weight oil when hot. 30 weight oil is always 30 weight. So when it is cold it is too viscous which is not good for the engine. Multi weight oils are a great invention and should always be used in my opinion. The only place that straight 30 weight oils should be used are in small engines which run really hot and can break down multi weight oil and you don't run them in the winter anyway.