Exactly 25W50 according to the J300 viscosity tables can pump down to -15C and can crank down to -10C. That makes it a suitable winter oil for me. Not that I would. But it makes my 15W40 seem like a walk in the park for cold starting.Before I decided to try the 25W50 in my SBC I was surprised to find the rated temperature range for this oil was from -15 oC.
I will never start at a lower temperature than 15 o C, so it's well above the rated range.
This is a special application, so probably outside the discussion here but is a bit relevant when a 25W is considered good for 'mild' winters.
Was that 25W50 you referred to Castrol Edge? That's only one that I know of. I assume you have a worked V8.
Edit: Don't worry I see you answered my question earlier
" I use the 25W oil in a race 355 SBC I blue printed myself. It has bearing clearances and oil pump to suit, and I drilled the lifter galley plugs 30 thou for timing chain squirters to quickly bleed the oil gallery of air pockets.
I use Castrol Edge 25W50 for the valvetrain, which is stout."
Last edited: