Hi,
The old 194 in my 64 Chevelle was well worn, leaky, a little smokey, and generally tired.
In an attempt to prolong it's stay in the car I tried twice to change from 10W40 to 20W50 Castrol (original GTX)
Both times the valve train seemed to go nuts, clacking noises from seemingly all the lifters and valves.
Dumping the oil and going back to the 10W40 would fix it.
I never really understood what the problem was.

Couldn't be collapsed lifters?
Lifters pumped up and stuck?
Anyone have an idea on what was going wrong?

Thanks

what is your oil pressure with the 10w40?

While the bottom end ( rings, bearings) can be loose with wear. And also the valve guides/ non existent seals. The lifters are very precise and do not wear much. Those tight tolerances probably do not want to pass thru that thick oil to the upper valve train thru the lifters.
Maybe try a 5w40 syn. Beware, it may leak more than conventional oil.

Hi,
The crude gauge in the Super Sports went from 0-60, so it must have been around 30psi, higher when cold, lower when warm.

Never put a real gauge on it so don't know what the actual pressure was.

I'm guessing it was a lifter related problem.

I pulled the engine and I'm putting a warmed over 250 in its place.
Not like I'm going to put the 194 back in the car to try and figure it out.

Just something that came to mind in case it happens again. Though I don't have any more 20-50 at my house.

I have run 20-50 in mine and never had issues, So has to be some sort of under lying issue ( Pick up screen, is first to come to mind. )

I saved the 194 in case anyone ever knocks on my door looking for a real deal 64 Chevelle SS with OEM 194 and PG!

Could be something wrong in the pan or pump, maybe this summer I'll have a look.

Thanks

I tried a similar thing in my 1991 Jeep with 4.0. It has just over 200k and I wanted to run a little thicker oil in it. I went with Rotella 15w40 and it didn't like it. I have ran 10w30 and 10w40 with no problems, but it does not like the 15w40. I just wanted something thicker for the bottom end, the valve train is fine.

When the motor is up to temperature, only the number after the W matters

I have always found discussions about motor oils spirited - yet at the same time plagued with misconceptions - especially with regard to hobbyist engines where the benefits of multi-grades and "long life" oil change intervals are largely irrelevant.

Is a 10 weight base stock fortified with 40 weight Viscosity Modifiers the same as straight 40?

Is a 15 weight base stock fortified with 40 weight Viscosity Modifiers the same as straight 40?

The multi-viscosity grades were created to allow for flow at freezing and even subzero temperature winter starts.

What hobby car is being pressed into service on a -10F morning to go to the office/shop?

In my mind Viscosity Modifiers are simply a compromise for winter driving - without the need to change out the crankcase contents. Absent the need for cold starts - base 20W, 30W or 40W (without modifiers) is the best choice for certain antique engines.

So the number on the left does matter.

A "cold start" occurs every time the engine is started... even in Saudi Arabia.
No 212 degree (post-W temperature rating) ambient temperature exists.

here is pretty good video on oils.