Originally Posted By: tig1
Originally Posted By: Merkava_4
I'll answer the question: Going down a grade is bad because it gives you no room for shearing like the thicker grade does. 5w30 can shear down to a 20 grade, but what's 5W-20 gonna do ?
I used Mobil 1 5w20 in the late seventies in engines calling for 10-40. No problems.
But we've covered, over, and over, and over again that eh original Mobil 1 5W20 was created using zero in the way of VMs, and before the days when HTHS was included in J300...it's HTHS was likely 2.9 (like Redline's offerings, built the same way)...and it was running against 10W40s, which back in the day were a dog of an oil, and when J300 FINALLY included HTHS minimums, they were put at 2.9 also (and some of them didn't even make THAT, in having to make it the minimum).
To infer that a modern ILSAC 5W20 (2.6HTHS) could replace a modern 10W40 (3.5HTHS) using 40 year old marketting as evidence is a bit of a long bow to draw (I get slammed is an SAE paper that I present here is older than 10 years).
Originally Posted By: Merkava_4
I'll answer the question: Going down a grade is bad because it gives you no room for shearing like the thicker grade does. 5w30 can shear down to a 20 grade, but what's 5W-20 gonna do ?
I used Mobil 1 5w20 in the late seventies in engines calling for 10-40. No problems.
But we've covered, over, and over, and over again that eh original Mobil 1 5W20 was created using zero in the way of VMs, and before the days when HTHS was included in J300...it's HTHS was likely 2.9 (like Redline's offerings, built the same way)...and it was running against 10W40s, which back in the day were a dog of an oil, and when J300 FINALLY included HTHS minimums, they were put at 2.9 also (and some of them didn't even make THAT, in having to make it the minimum).
To infer that a modern ILSAC 5W20 (2.6HTHS) could replace a modern 10W40 (3.5HTHS) using 40 year old marketting as evidence is a bit of a long bow to draw (I get slammed is an SAE paper that I present here is older than 10 years).
