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30 Closed Cab PU · 10-06-2019, 10:42 AM

From my reading and understanding and my opinion

Zinc was not originally (late 20s/early 30s) an additive in oil. Zinc was added when higher compression motors were developed that revved /ran at much higher RPMs, which required much stiffer valve springs to prevent valve float. The Zinc was added as an anti-wear agent.

I do use T4 Rotella diesel oil. It is relatively inexpensive, available almost everywhere, has some zinc. Even though my opinion is Zinc is not needed, what the heck should not hurt anything. Lots of A people use Rotella, and have not seen/heard complaints. It may not be the "best" oil, but is a decent oil, and I change frequently, at 500 miles. I am a big believer on stock Model A motors without an oil filter, frequently changing oil is more important than what type of oil is used. If running an oil filter and extending oil change intervals, the type of oil used may have some effect.

I have read that overuse of Zinc Additives causes changes in metal that causes it to become brittle like. So more Zinc than recommended is not better. So if adding you need to know how much is in the oil you are using, and add only an appropriate amount.

As far as the amount of Zinc in Rotella, I am confused, but it does have some. I am unsure, but lean towards Mike's info in post 14. I've seen info online and in forums that support that the amount has been reduced, and other info that contradicts saying it has the required amounts.

I've also seen discussion about detergent vs. non detergent oil The detergent is not like a soap/thinner, it only acts to keep contaminants suspended in the oil until it can be drained. It does not break up existing sludge into globs. On the other hand the non-detergent oil some contamination stays suspended, and some settles. I suspect that in the day part of occasional maintenance was to drop the oil pan and open the valve access cover and clean out the sludge. Something the average owner who did his own oil changes most likely did not do.

So which is better on stock motors/no oil filter? Detergent oil which keeps all contamination suspended in the oil and going through the moving parts (EX - Babbitts) of the motor but keeps surfaces free of sludge, or non- detergent oil which may keep some contamination out of the oil but requires periodic dropping of the oil pan and opening the valve access cover for cleaning?

Choices seem to be running an oil filter, or frequent oil changes.

Since I am lazy, I prefer detergent oil with frequent oil changes since I do not run an oil filter. I also prefer detergent oil since it is multi weight which aids in reducing wear on the motor until the motor is warmed up.

10-06-2019, 10:42 AM	#16
30 Closed Cab PU Senior Member Join Date: Aug 2018 Posts: 2,332	Re: ROTELLA 15W 40 Oil From my reading and understanding and my opinion Zinc was not originally (late 20s/early 30s) an additive in oil. Zinc was added when higher compression motors were developed that revved /ran at much higher RPMs, which required much stiffer valve springs to prevent valve float. The Zinc was added as an anti-wear agent. I do use T4 Rotella diesel oil. It is relatively inexpensive, available almost everywhere, has some zinc. Even though my opinion is Zinc is not needed, what the heck should not hurt anything. Lots of A people use Rotella, and have not seen/heard complaints. It may not be the "best" oil, but is a decent oil, and I change frequently, at 500 miles. I am a big believer on stock Model A motors without an oil filter, frequently changing oil is more important than what type of oil is used. If running an oil filter and extending oil change intervals, the type of oil used may have some effect. I have read that overuse of Zinc Additives causes changes in metal that causes it to become brittle like. So more Zinc than recommended is not better. So if adding you need to know how much is in the oil you are using, and add only an appropriate amount. As far as the amount of Zinc in Rotella, I am confused, but it does have some. I am unsure, but lean towards Mike's info in post 14. I've seen info online and in forums that support that the amount has been reduced, and other info that contradicts saying it has the required amounts. I've also seen discussion about detergent vs. non detergent oil The detergent is not like a soap/thinner, it only acts to keep contaminants suspended in the oil until it can be drained. It does not break up existing sludge into globs. On the other hand the non-detergent oil some contamination stays suspended, and some settles. I suspect that in the day part of occasional maintenance was to drop the oil pan and open the valve access cover and clean out the sludge. Something the average owner who did his own oil changes most likely did not do. So which is better on stock motors/no oil filter? Detergent oil which keeps all contamination suspended in the oil and going through the moving parts (EX - Babbitts) of the motor but keeps surfaces free of sludge, or non- detergent oil which may keep some contamination out of the oil but requires periodic dropping of the oil pan and opening the valve access cover for cleaning? Choices seem to be running an oil filter, or frequent oil changes. Since I am lazy, I prefer detergent oil with frequent oil changes since I do not run an oil filter. I also prefer detergent oil since it is multi weight which aids in reducing wear on the motor until the motor is warmed up.