Jim Rogers

c4 l83 and l98 engines (before 1987) have flat tappets. Recently a raging debate has developed as to whether today's motor oils, with their EPA-mandated lower levels of the anti-wear additive zinc (zddp), are capable of fully protecting flat tappet valve-trains. Searching the internet, one can find literally thousands of pages of debate on this issue. This is an unfortunate situation for owners of l83 and l98 engines who just want to perform the simple task of changing oil without taking a risk of causing premature wear and/or failure.

So I decided to do a little amateur research into the zddp issue. I have done a fairly extensive review of the literature; my job allows me access to peer-reviewed primary research papers, and many SAE and ASTM research reports can be found online. I could not find all of the SAE papers freely available online, so some had to be purchased at my own cost (at 24 bucks a pop-- hope you guys are appreciating this!).

I have completed my analysis of the literature and I believe that there is a clear answer to this question. There already is a large and informative thread on the c3 forum on this topic, but I thought it would be good to have a c4-specific version in order to help any of our members who, now or in the future, find themselves wrestling with this issue. So this post is designed to be a concise and definitive summary specifically for our community.

Executive Summary

Today's API SM/SN oils with zddp levels at 800ppm are just fine for your *stock* l83/l98 flat-tappet valvetrains (as well as all post-1986 roller-tappet l98 engines). If you have modified your valvetrain for high performance, you are well-advised to use oil with >1000ppm zddp. Even in the case of modification, unless your mods are extremely radical, there is no need for more than 1500 ppm zddp.

Details

There are a number of laboratory bench studies of zddp and metal wear (and I have read many of them!), but I believe the gold standard is probably actual engine testing. The standard test is the ASTM Sequence IIIG Engine Oil Test, and the most relevant part of that test is the Average Cam Plus Lifter Wear component.

Here is how the IIIG test is performed: They take a GM 3800 Series II V6 and retro-fit it with flat tappet lifters with 205 lb open pressure springs and 1.67:1 rocker arms. This results in a final static lifter load of 350 lbs (180,000 psi). They run that engine for 100 hours at 3600 rpm and an oil temperature of 302 degrees F. This is an extreme test intended to duplicate the stress of a pickup towing a loaded cattle trailer in the desert.

After the 100 hours, they measure (among other things) the average wear of the cam plus the lifter, and that wear must be less than 60 microns in order for an oil to pass the standard for API SM/SN/SL/SJ rating. As the table and graph on pages 36 and 37 of this research report show, ASTM reference oils 434 and 435 (both 800 ppm zddp) are able to pass this test with ease-- their average wear is 36 microns.

So that's the test, but one of the big questions about it is whether that test is applicable to our flat tappet c4 engines. The answer is-- yes. Both the l83 and l98 (in stock form) have 220 lb open pressure springs with 1.5:1 rocker arms for a total lifter load of 330 lbs-- less than the IIIG test engine. Furthermore, 305 degrees is a far higher temperature than the majority of Corvette owners will see even briefly, let alone for 100 straight hours. And 100 hours of 3600 rpm in the Sequence IIIG test is equivalent to driving my c4 (with a stock 700r4 transmission) at 125 mph continuously for 12,500 miles (with that 305 degree oil)-- this is more like hard racing conditions and these conditions are much more extreme than most stock Corvette owners will subject their engines to in the course of standard oil change intervals.

So, if anything, the l83 and early l98 engines have *lower* lifter loads than the IIIG test engine and the IIIG test parameters are far *more extreme* than the vast majority of Corvette owners will experience in practice. Therefore it is an inescapable conclusion that any oil that passes the IIIG test will definitely work in our (stock) engines.

So the bottom line is that 800 ppm SM/SN oil is definitely adequate to protect our stock flat tappets from undue wear.

So why is there such a controversy out there? There are a number of reasons (including manufacturing issues discussed below), but I would say the biggest problem comes when one modifies the valvetrain for high performance. A typical mod for the l98 is to replace the stock 1.5 rockers with 1.6's, which requires a stiffer spring. A common spring for this mod is the lt4 which has (I believe) 280 lbs open pressure. That's a total of 448 lbs of lifter load-- well above both the 330 lb stock value and the 350 lbs used in the IIIG tests.

As far as I can tell, there is no standardized testing for this kind of high lifter load, and it is entirely possible (and probably likely) that 800 ppm zddp is not adequate for this type of application. For this type of high-load valvetrain, oil with >1000 ppm zddp is recommended. Furthermore, it appears that only extreme valvetrain parameters (>600 lbs load) require more than 1500 ppm. Using more zddp than necessary is not advised-- it can actually harm the engine by increasing wear.

So the final word is: 800 ppm zddp is adequate for our (stock) l83 and l98 flat-tappet engines, and there is no requirement to use any higher levels-- end of story.

So why should you believe my analysis over all the dire warnings you can read on the internet? It's true that I'm not an expert; and at this point I should say that what I've written here should be considered my personal analysis that I'm sharing (rather than a recommendation to anyone). But here are two reasons why my personal analysis might rise above the internet noise:

1. As I mention above, my job allows me access to scientific literature and I have actually read the papers that most are discussing on the basis of second hand knowledge.

2. Until I did this study, I was an advocate of the “800 ppm zddp is not enough” position in the debate. Not that I had any inside information, but the internet debate had me worried and I felt that one should err on the side of caution. Thus I had every incentive to skew the analysis, interpretation, and findings of the current analysis to show that my previous position was right. However, upon reading the available literature, I am now concluding that my previous position was incorrect; the fact that I am publicly acknowledging that should give some confidence that I have performed a fair and unbiased analysis.

However, if you don't trust me (and it is always possible that I'm wrong), you can read for yourself the technical details. If you wish to do so I have some recommendations to help you cut through the crap and get to the useful data and analysis. After having read the primary literature, I can recommend these reviews as having accurate summaries of that data and information:

1. This article is the best. The papers they cite are indeed the best ones (I've read all of them and more), the experts they consult are the most knowledgeable (in particular, Bob Olree-- GM Powertrain Fuels and Lubricants Group, really knows his stuff), and their interpretation of the data and information is spot on. [Of particular note, it also goes into the history of the entry and exit of various cam and flat-tappet manufactures in the market. Quality issues with various manufacturers probably was a large part of the problem, but I chose not to repeat all that history in this post; it's relevant, however, and you can get the details on that in the article.] You need only read that one article (read all six parts!) to be well-informed on the whole zddp issue.

2. This article is also comprehensive and, I believe, technically correct.

3. This exchange (see posts #1 and #8) is also very good. Both points of view are completely correct and supported by the data. Notice that the reason for their contradictory positions is the performance level-- as I discussed above.

4. This famous post and subsequent thread on the c3 forum is also correct in it's presentation of the problem. Again, notice that it's the level of performance that's critical-- stock is OK with 800 ppm, modified is likely not.

So as far as I'm concerned, this issue is resolved. So nothing more to say, right? Well, not quite...

For those that are interested in *marginally* better protection for your precious baby (that would include me!) or if you have modified your valvetrain in such a way that lifter load is increased, then there is a little bit more we can discuss.

Consider these facts:

1. If you look at the p. 37 of the chart I referenced above, you can see that the average value for cam+lifter wear for 800 ppm oil is 36 microns, well below the 60 micron pass limit. But the standard deviation is high; in some tests (e.g., reference oil 435), the values for one of the oils were near 50 microns which, while still a passing score, is getting close to the 60 micron pass limit.

2. In the same chart, reference oil 438 (currently designated 538) with 1024 ppm zddp only showed 20 microns of wear, and the standard deviation is low. So while 800 ppm oil is acceptable for long engine life, 1000 ppm is significantly better.

3. While the test shows that 800 ppm is within spec, note that the SM/SN standard is actually between 600 and 800 ppm. So it's possible that the SM/SN oil you're buying has as little as 600 ppm. There is also (normal) production variance, so actual additive values of any nominal 600-800 ppm oil could actually be less than 600ppm. In addition, zddp degrades as the oil life is used up-- so whatever level you start with will be lower as you drive. In other words, it's possible that the SM/SN oil your using is starting at 600ppm (or less) and ending below 300 ppm-- not good. So starting with >800 ppm will give you some cushion to mitigate that possible scenario.

4. If you have a high performance flat-tappet valvetrain, you almost certainly need >1000 ppm oil, and if you have a high performance roller-tappet valvetrain you might want the same because of the possibility of the rollers “skating.”

So while it's not necessary, it's also not unreasonable that some c4 owners (both flat- and roller-tappet) would want to use higher zddp oil; for reasons 1-3, I personally am still inclined to use >1000 ppm oil in my 1985's. It will cut the (already acceptable) tappet wear in half, meaning I won't be as close to the limit, plus there is an extra cushion to ensure that there is enough zddp over the entire use cycle of the oil. Since it's not difficult or expensive to get >1000 ppm oil, I say there's no reason not to use it.

So how will I get >1000 ppm oil? It's easy:

Option 1 (Cheap and Easy): Mobil 1 High Mileage is an API SL oil, so it is allowed (and VOA's show it actually has) 1100 ppm zddp and it comes in the required 10w-30 weight. Because it's an API SL rated oil, that means it's the most current spec oil for engines built before 2004. So technically speaking, if one was to follow the absolute spec oil for our engines, it would be this one. While current today, I expect SL will become obsolete in the near future (as all old standards have) and disappear. What to do then? See the next options.

Option 2 (Cheap and Not Too Difficult): You can mix your own. Using a oil mix calculator, you can see that mixing 3 quarts of Mobil 1 20w-50 (a 1300 ppm oil-- oils above 10w-40 are exempt from zddp standards) with 2 quarts of Mobil 1 5w-20 (900 ppm) will yield 5 quarts of 10w-30 (actually 9.43w-28.24-- which is *very* close) oil with 1140 ppm zddp. Perfect! Other desired viscosities can be created using different ratios. And, btw, it is confirmed by Mobil 1 engineers (see here and the fourth post here) that this sort of mixing is not at all prohibited and will work as well as either one individually.

Option 3 (More Expensive and Not as Convenient): Buy a boutique oil (Amsoil, Driven, Brad Penn, etc.). This post is regularly updated with information as to what's available.

Finally, there are some options that I personally have rejected based on my study:

Rejected Option 1: Using diesel (“C” series) oil in a gasoline engine for its higher zddp levels. This is an iffy proposition due to inherent differences in temperatures and operating conditions for these two very different types of engines. In publication SAE 860373 (sorry no link-- I bought this from the SAE and it's copyright protected), Figures 7a and 7b show that diesels are not as sensitive to detergent formulations, are well-protected with only primary zddp (i.e., the less effective kind), and do not need secondary zddp for adequate protection. All this is different in gasoline engines.

Rejected Option 2: Adding zddp additives to 800 ppm oil to increase the level. I believe that zddp additives are questionable. As evidence of this, in publication SAE 860373 (again, no link), Figures 5 and 6 show that the ability of 800ppm zddp to provide protection is highly dependent on the detergent package used. Depending on the detergent formulation, 800ppm oil can pass the Rocker Arm Distress Rating test with scores of 0, 5.6, or 6.9 (Pass Limit = 10), or fail it with ratings of 29, 30.6, 44,4, or 62.5! That's right-- detergent makeup can allow the same 800ppm oil to either pass the test by 50%, or fail it by six times the limit! Big difference! So adding an additive might work to improve your oil, but it might make it worse-- possibly much worse. Unless you know the exact composition of the additive package in your starting oil and the exact chemical composition of the zddp additive you're adding, I believe you're just gambling by simply dumping in a zddp additive.

Rejected Option 3: Cheap, generic brand oil. While often made by major manufacturers, VOA's often show that they are basically made from “leftover” bases with minimum (and sometimes lower than allowed) amounts of additives (for example, see page 14 here). These products are made to a price point and there is a decent probability that corners have been cut to meet it. It's possible that there are cheap oils out there that are good, but it's more likely that the cheap brands start with no more than 600 ppm zddp, and corner cutting could mean there's actually less. You really have have no way of knowing which quality you're getting. These cheap oils are good enough for a car you don't care about or won't keep for long, but I wouldn't put it in a classic Corvette that I planned to keep. Checking prices at my Walmart, the cheapest oil they sell is only $2/quart less than the Mobil 1 options listed above. No way I'm taking a risk with my Corvette to save a total of 10 bucks on once a year (at most) oil changes.

So there you have it-- flat-tappet c4 owners, fear not! The evidence is pretty solid that modern 800 ppm zddp oil will keep your engine happy throughout your entire life, and it's not difficult to find or create 1100 ppm oil that will keep those tappets in great shape many years (and miles) from now when your great-grandkids own it!

BBNJKen

Please admins, this has "Stickie" written all over it!

JrRifleCoach

Too much conjecture. Nicely written and formatted though.

Jim Rogers

Yes-- some conjecture on my part, but that conjecture is based on and supported by a published (and cited) SAE report.

cv67

Inclined to agree
Stock type cams rarely if ever go flat,when they do its usually many yrs and miles down the road
Imo where problems pop up are the trendy "fast or extreme" ramps that have more shearing action. Add more valvespring, perhaps a slight loss of valve control, not so great quality aftermarket cores and you see another premature failure posted, even on rollers.

GM could have easily put more aggressive cams in these and made more power theres a reason (warranty) they didnt. Plus they know we cant keep our hands out of things and probably will muck with it anyway

Seems theres a line between picking up the valvetrain events and still building some reliability into it. On my current solid roller the ramps are anything but extreme....3 yrs and 0 loss of spring pressure lifters are in great shape. Not many miles, but still....

Opinions may vary.

JrRifleCoach

Just saying, remove the conjecture (opinions) and let your empirical evidence stand on its own.
You give a great view on an old topic that few have devoted this much effort towards.
Its a great post.
Thanks for your effort.

GREGGPENN

I'm not sure this was as much an issue of conjecture as phrasing. Considering what was conveyed, I thought it was pretty clear and well-written. I really enjoyed reading it!

As for additives being questionable, it was obvious he meant their results -- when combined with oils at random. By using additives, you may or may not improve on the prior protective qualities of oil. I've read this myself before. It is supposed to be good writing style to clearly state where you are heading with your details and conclusion.

GREGGPENN

With what? ZDDP is or isn't necessary? Or that it should be used at all? Or that it's use should be analyzed?

Seems like you're saying you aren't worried about it's use/presence.

I think...

bogus

I think Ron's agreement was a general one to the topic...

much like my thoughts.

I was surprised to learn that mixing different oil weights actually creates an average.

cv67

Im saying its important but huge levels not needed, ash and other ingredients have a play in there too. I dont hesitate to grab a qt of house brand stuff if Im a qt low and in a rush just dont see how thats going to wreck a motor.
Basically dont lose sleep over it lol.

Tommycourt

What about engines that already have high mileage on them. I am sure GM was using all new componets when they did the assembly and testing. High mileage vehicles (100K+) already have existing wear and perhaps their tolerances are marginal. Is that taken into consideration? Also on my dipstick it reads to use 5W-30 oil. Would that also be taken into consideration? I do not doubt your analysis nor your facts but I think there may be more variables taken into consideration as we don't drive in a test lab. I live in Az where when you die and go to H*** you want to take a jacket cuz it's a cooler climate.
Tommy

36Volt

Cool write up. Data is there, I don't mind the conclusionary narrative.
Personally, the worst flat cam/valve train wear I ever seen was the late 70's early 80's Chev small block FLAT CAM SYNDROME. Dealt with 100s of them.
I know oils have come a long way. Personally (I have 13 cars some as long a 35 years) I use only shale based oils and my engines have some serious miles on them and cams are usually not that bad when I refresh one, (usually 150-180,000 miles) My 77 Vette have 5 flat lobes when I got it, one was nearly round (no lift) could tell had paraffin based oil in this engine. paraffin is the WORST to heat tank out, ALL THAT CRUST ARGH!
I do not find as much concern with levels of zinc as engineers to oils are not ignoring the protection requirements, just doing it a different way.

Silver96ce

Jim, thanks for the research and write-up. It was a good read. Over the last few years I've wondered about the claims about ZDDP (I have an '67 Mustang that I am hoping to do a full restomod in a few years). It seems that the issue is more hype to create sales of additives rather than actual need for increased ZDDP. I thank you and my wallet will thank you when I actually get around to working on the old car.

Tom400CFI

I agree. That was some of the best reading I've had on this forum in a long time. Great presentation, fantastic documentation....strong work there and a real contribution, I feel. I second the suggestion to make is a sticky. That was good quality reading.

JackDidley

Cliffes notes ??

Geardo

Like 36 volt said, small block Chevy's are notorious for cam wear

Jim Rogers

Yep-- I'd say you're correct on all points.

You're welcome. All data requires analysis and interpretation-- that's different from "opinion." Unless there were specific experiments done to address all points, it's required (and normal) to make some inferences based on the data.

I wanted to address the zddp additive question, but found no direct testing so I made inferences (similar, but different from conjecture) about that question based on the data I found. That inference was based on the empirical evidence and, I believe, was correctly made.

Glad you liked it Gregg. As far as the additive question, I believe it was clear: I did not find direct testing, but there was plenty of other testing (e.g., the cited detergent testing) that indirectly indicates that zddp additives are questionable. Note that the conclusion of "questionable" is not as conclusive, but that's because it's based on inference. I think it's appropriate as written.

I was surprised as well-- did not know that until I did this study. Note that it's not an exact arithmetic average (it comes out a little lower) thus necessitating the use of the cited calculator.

Agree with all those points.

No tests can be standardized to take into account all factors. The process of the ASTM Sequence IIIG test development was quite long and there were many, many rejected drafts. The part of the test I focused on (ACLW) did not address viscosity or high mileage engines; it was designed only to test for the ability of oil to protect a valvetrain from wear. Your questions are different (and beyond) what they were testing and what my post is addressing (i.e., is 800 ppm zddp oil adequate in a c4 engine?).

I have read about the history of Chevy "soft cams" but, due to length. decided to leave that out. Agree that oil engineers know what they're doing. Until I did this study it was a question in my mind-- engineers may know what they're doing, but are the EPA mandates such that it's impossible for them to create an oil that meets the mandate and offers enough protection? I conclude that the answer is that they can and have.

You're welcome-- glad you liked it and glad it will help you.

An Executive Summary was included for those that just wanted the answer I came up with and were not interested in the details of how I came up with that answer.


I have read that but did not include that aspect in my analysis due to length. That's right-- what I posted was actually edited for length!

Glad that you, in particular, liked it. And the best part-- it totally proves that your were right and I was wrong in our previous discussion! Bet you've never debated anyone that went to so much trouble to prove that *you* were right!

As far as your comment in the other thread:

It's true that this study cost me some cash, but I didn't mind. I'm always working on my '85's, but I don't post here much because a quick search of the archives always gives me the answers to any question I have.

While I have some experience working on cars, I don't consider myself to be any kind of guru so I usually don't feel qualified to contribute to the forum.

So when I saw that I had the opportunity to actually contribute something of value, I jumped on it and didn't hesitate to pay for any articles I needed.

I would be incredibly honored if this thread became a sticky-- I would feel that I actually did something to re-pay this community for all the help they've given me over the years.

hcbph

Quite an impressive writeup, I learned something from it. Thank you for your time and work in creating this.

C409

..... Thanks for re-iterating the obvious ... your presentation is about 15 years late ... How many of you buy extended warranties on things just because or just in case ? ... I believe I will continue to supplement the blood of my engine , regardless of the conjecture "discovered" here ......... Just because AND just in case ! .....

JackDidley

That works. I have a motor on the stand with a solid lifter, flat tappet cam. It will probably get a roller before it goes back in a car.