Motor Oil: Zinc and Other Myths

There's a lot of well-intended advice floating around about "zinc" in motor oil, including allegations that the latest (new car) oils are harmful to our old cars.

While I'm no expert on this, I am fortunate to have a good friend who IS just such an expert, as well as a member of our hobby. While he is, by nature, a modest individual that likes to stay out of the controversy, I felt it would be helpful to the collector car community to share some of my friend's knowledge on the subject. His attached document about various historic myths surrounding motor oil is both factual, as well as entertaining, and was written to respond to the numerous requests he receives on the topic. Note that it addresses the alleged "zinc issue" very well. (See attached PDF file)

By way of introduction, Mr. Robert Olree is one of the foremost experts on motor oil in the world. His careers at Ethyl Corporation and GM Research are marked with considerable recognition for his extensive contributions to the industry. Among his many technical publications is an SAE research paper (#2004-01-2986) entitled "How Much ZDP is Enough". Due to copyright restrictions, I cannot post this document, but it is available through SAE and most technical libraries (Universities, etc) can obtain it for you. Anyone interested in fact-over-fiction on the zinc topic should read it.

For those that want the bottom line, it is this:

1. Current modern (i.e. "new car") oils contain adequate "zinc" for protection of flat-tappet engines that are already broken-in.

2. Appropriate assembly lube should continue to be utilized on new cam & lifters to prevent scuffing during break-in. However, these assembly lubes (like GM Engine Oil Supplement & Assembly Lube) should NOT be used beyond break-in period (see #3 below)

3. Excessive "zinc" additives can actually cause excessive wear and should be avoided.

Engine Oil Mythology 2-2007.pdf

Very interesting article, I often wondered how true some of those claims yoo read about this subject. Thanks for sharing this information. I printed out the attachment and will read through it more carefully.

Greg,

Thanks for giving us this information. It may save problems with our older engines because of the addition of too much zinc causing unnecessary wear. I had considered using an zinc additive in my cars and now I know better.

Greg,

Can I get permission to reprint this article in our newsletter?

Thanks,

Greg,

Can I get permission to reprint this article in our newsletter?

Thanks,

Mark,

I don't think that would be a problem, but let me verify with Mr. Olree. I know he's sent it to a couple of car magazines that wanted comments from him.

I will also try to get a more concise (but brief) bio on him, so that the article will carry the appropriate credibility when published in your newsletter.

Greg

Here is the response from Shell Oil

Clifford,

With the introduction a couple of years ago of ILSAC specification GF-4

and API specification SM for gasoline-only engine oils, the amount of

phosphorous in the oil had to be reduced to prolong the life of

catalytic converters. Zinc-based anti-wear compounds, which also

contain phosphorous, were reduced as well. These zinc compounds work

well to protect flat tappet engines from excessive wear, so the modern

gasoline-only engine oils are not as effective in this regard as they

once were.

Diesel engine oils don't suffer from the same requirements to protect

catalytic converters, so the amount of zinc-based anti-wear additives

remains high. Products like Shell Rotella T Oils, which also carry API

S-series licenses for gasoline engines, have found favor for flat tappet

engines.

There has been a recent change to the API specification required for

oils used in 2007 big rig diesel engines to reduce particulate

emissions, API CJ-4. As a result, the zinc content in Shell Rotella T

Multigrade Oils has been reduced slightly from about 1400 ppm to about

1200 ppm. Even at these slightly decreased levels, Shell Rotella T

Multigrade Oils still have at least 50% more of these anti-wear

additives as most current gasoline-only engine oils. These levels of

zinc have historically offered good protection in flat tappet

applications.

Shell Rotella T Oil SAE 30 also contains about 1200 ppm zinc. Both the

SAE 30 and SAE 10W-30 grades would be most readily available from our

distributor network. Distributors may be found by using the locator at

http://www.shell.com/home/PlainPageServlet?FC=/rotella-en/html/iwgen/whe

re_to_buy/app_wheretobuy_distributors.html.

Thank you for your interest in Shell Rotella Products!

Regards,

Edward Calcote

Staff Chemist, Shell Lubricants US Technical Information Center

http://www.rotella.com/

Yes, but Rotella oils are not available in the 20W50 weight that most earlier high performance engines should really use. The 15W40 weight comes close, but for extended use (like touring) there could be definite loss of both oil and lubrication.

Meanwhile most non-partisan sources agree that ZDDP levels have not yet been reduced enough to impact normal (non-break-in) engine wear in nearly all flat tappet engines except for extreme high-performance motors.

So which risk are you willing to take?:confused:

I do NOT recall any OEM's recommending 20W-50 for their engines, other than some particular BMW engines which are something like 10W-60. When most of the vintage engines we might have were built, 10W-40 and 10W-30 were more likely choices. Still, I have used GTX20W-50 in two of my cars (over the years) with no problems . . . other than one of them feeling "doggy" until I changed to 10W-40 (which had very similar throttle response as normal 30-weight oil). In the earlier 1970s, use of 20W-50 was mentioned, but with the same temperature range as normal 30-weight oils.

To me, the real operational difference between 15W-40 and 20W-50 or 10W-40 would be minor, IF there was a desire to have 20W-50 oil in a time of lowered zddp additives (when the diesel CJ-4 oils still had more of it). With the 15W-40 oil having slightly better low-temp pumpability than 20W-50, using 15W-40 would get things lubed quicker on a cold start (the reason for the 0W-30 oils).

There have been some orientations about the additives in diesel-spec oil not being "correct" for a gasoline engine use. To me, they are better. Diesels produce soot which can find its way into the oil, plus fuel dilution from blow-by past the rings. Think of soot being the equivalent of "dirt" in a gas engine, plus the combustion gas inclusions. In other words, what a diesel oil might have to deal with on a normal basis in a diesel engine are not that prevalent in a gasoline engine, so things should work better. It seems that those who advise against using a motor oil originally designed for diesel use (with gasoline engine approvals, too) are trying to sell a product or additive to add to SM-rated gasoline engine motor oil--by observation.

If you look at some of the Shell Rotella T ads for the later CJ-4 over the prior CI-4 oils, the CI-4 oils didn't do quite as good of a job with internal oil pan cleanliness as the newer CJ-4 Rotella T did.

Now, the information from Shell mentions the "dino" Rotella T 15W-40, but there is also a synthetic Rotella T 5W-40 also, with similar zddp levels.

Thanks for posting that information, Straight Eight! Highly informative!

NTX5467

I do NOT recall any OEM's recommending 20W-50 for their engines, other than some particular BMW engines which are something like 10W-60......

My TR6 engine, which is hardly an exotic motor (2.5L straight six, pushrods, etc,), was designed to use 20W-50. It is the only weight of oil recommended for temperatures above 30 degrees F by British Leyland. I think virtually all British sports car engines are similarly recommended.

My TR6 engine, which is hardly an exotic motor (2.5L straight six, pushrods, etc,), was designed to use 20W-50. It is the only weight of oil recommended for temperatures above 30 degrees F by British Leyland. I think virtually all British sports car engines are similarly recommended.

Is that recommended for the time it's in the shop, or on the road? ;)

Sorry Dave, but somebody had to take that shot at British cars.

My little bit of research on B-L TR6s and motor oil did reveal that almost everybody uses Castrol 20W-50 in them. One poster mentioned that he did go to 10W-40, but the oil pressure at idle was 15psi, compared to 40psi with the 20W-50. I also found a recommendation from Penrite for 10W-60 in older British cars.

I could not find an owners manual to look at, just posts from people that use 20W-50 in their Brit cars.

One poster mentioned that oil leaks might be more prevalent with 10W-40 than 20W-50. Using 10W-40 would let more of those low-tech horses get to the flywheel, even if it might leak a little more!

Regards,

NTX5467