Packard Forum Index » V-8 (1955-56)

Shell Rotella T4 10W-30 should work fine in your application. It's a diesel oil which doesn't have the tight restrictions on the ZDDP of the modern oils sold for gasoline engines. It's a lot less expensive than the specialty oils and will work just as well.

I ran Rotella T4 10w-30 for years in my old cars. I think it's a perfectly good oil that will do everything you need it to. Samples that I sent off tested at something like 1000 ppm of zinc and 800 ppm of phosphorus.

I consider AMSOIL Z-Rod superior. I switched to it after Rotella became expensive and hard to find.

If synthetic oil is scary to you, then I recommend Penngrade 1 (formerly Brad Penn).

10w-30 is perfect for year-round use in most climates in the United States. Show cars that are only driven in the south in summer can use 10w-40 or 20w-40, but I wouldn't use anything thicker than that. Using thick oil to raise oil pressure is focusing too much on a number on a gauge and not on what the oil actually does in the engine.

Modern cars do the same thing. 10w-30 is not to imply that oil viscosity is constant. It means the viscosity when cold is equivalent to a 10 weight oil and when hot a 30 weight oil. The 10 weight oil cold has a higher viscosity than a 30 weight oil hot.

The rule of thumb is minimum 10 psi per 1000 rpm oil pressure. With the standard ratio the motor is turning around 2,500 rpm at 60 mph.

Some years ago I was selling my 1939 Cadillac 60 Special. These cars had the 346 cu. in. L-head V-8s. The car burned a lot of oil. To mitigate this high use I used a 20W-50 engine oil. One of the potential buyers had a Cadillac expert come and inspect the car for him. He lived out of the area. The inspector was an engine engineer for Caterpillar. He said using the heavy weight oil was a bad idea. He said the engine was not designed for such heavy viscosity oil. The problem was the effort the oil pump needed to circulate the oil. It put too much strain on components. Also, he said it would not cure the oil burning problem. This was due to worn rings. He also said it would not cure low oil pressure. Although, there was no problem with this. He was right. Reading Tim Cole's comments brought it all back. You can't fix problems without parts.