ZDP & Flat Tappet N*

[Rich]

I know this ZDP issue has been discussed at some length here, and I've tried to absorb as much of the salient information as possible, but I still seem to finding conflicting information. I have a 1997 N* with 91K trouble free miles. I'm somewhat reluctant to switch to oils intended for diesel applications as some have suggested. I'm also not sure I want to add GM EOS to my fill as I've read that modern oils are rather complicated chemical formulations (which I'm sure they are) and simply adding something to the crankcase will not necessarilly have the desired effect.

I called several oil companies for their opinions. Mobil is a bit hush hush on the ZDP subject and won't really cite specifics, stating the information I'm requesting is proprietary. They then suggest I switch (from Mobil 1) to one of their diesel formulations to alleviate any concerns I might have. The fact that they don't come straig out and say there is nothing to worry about makes me worry. Quaker State/Pennzoil/Shell (same phone number for all) told me to use their Rotella product for diesels which still has the high levels of ZDP. Castrol actually pulled out some data sheets from GM as we spoke and then told me that GM recommends the use of SM grade 10W30 for use in 1996 and newer N* engines. The tech told me this was a recently published GM report. I wasn't aware of any valvetrain differences between pre and post 1996 N*'s.

Am I concerning myself with something I need not?

It's hard to imagine these oil companies marketing oils which will cause widespread cam failures in the field. Perhaps the problem is more apt to affect "vintage" vehicles as the Castrol tech initially indicated. When I said I was referring to a 1997 motor, the tech's concern seemed to lessen considerably. Perhaps the ZDP depletion issue is valid for older engine designs, but not for newer designs.

Sorry to beat a dead horse, but is this really a problem for post 1996 N*'s? Or for any N*'s for that matter?

[JimD]

This one is a judgement call Rich. I saved several of the posts by our former Guru on this subject and here is my interpretation of his comments.

API grades SL, SM contain the minimum levels of ZDP (zinc) as an anti-wear additive. The levels of ZDP have been reduced because ZDP can contaminate catalytic converters. The improvements in SL, SM oils include higher tolerance for temperature and friction modifiers to improve fuel economy. An engine designed to operate with SL, SM oils will have hardened wear surfaces and internal clearances compatible with the reduced levels of ZDP.

An engine designed and built when API grades SF, SG was the standard might not be placed at risk by using SL, SM oils. The Guru's words were "Older engines designed for the SF and SG oils that had more ZDP in them are not as well protected....". But he stopped short of saying 'do not use SM grade oil in a 93 Northstar'.

He did offer Rotella or adding a bit of GM OES as a viable oil alternative for 'older' engines. The problem as I see it is, where is the line between adding enough ZDP without adding more than the engine needs and run the risk of converter contamination.

I use Starburst 10W-30 in my '98 engine without worrying about it. I do not know when the oils at my local parts store became API grade SM so I don't know how many of my 154,xxx miles have been with reduced levels of ZDP.

Since I live south of I-20, I have no fear of using a heavier grade of oil; cold weather starts are not a concern of mine.

[KHE]

I can't find SL grade oil ANYWHERE. Even the Rotella 15W40 diesel oil is now SM rated... so, I've been adding 5 ozs of EOS at each oil change.

[Ranger]

I don't think it is anything to be too worried about. I use the SM oil in my wifes '96 Bonneville, but I believe it has roller lifters. Imagine the law suites if it would cause engine failures in older cars. They would not take that kind of a chance.

[Devin O'Conor]

I have been using Rotella T 10W30 ($8.88 per 4 quart jug at Wal-Mart) in my 1995 Northstar for the past 30,000 miles. I have been very happy with it. I never get the "Check Oil Level" message at all during my 3,000 mile oil change interval. I had one time when I had to have the oil changed in a garage that didn't have Rotella T and they put Maxlife in it. The "check oil level" showed up within 2,000 miles. Back to the Rotella T and it went back to the 3,000 miles without the message. I'll be sticking with the Rotella T. Also have it in a 97 Sunfire 2.2L and it works great and quiets the engine down.

[Jan Olsson]

Hi.

I would certainly use an oil in the SF or SG grades just because of the "right" amount od ZDP (ZDDP). That's what the engine is validated for, try something else than recommended and you'll be the one during the testing...

I once asked the Guru about just these things and though he didn't say it was bad, he said "not so good"...

Things might just work fine with a SL/SM or whatever but keep in mind that the amounts of ZDP has decreased from about 4% to 1/10 of that (if I remember correctly).

And now an example that might make sence to some of you? Here in Sweden when they stopped selling leaded fuel, the public recieved great info about that. The fuel then recieved Natrium as an addtive instead. Everything worked fine when they did that switch (regarding wear on cast iron seats/valves. But then suddenly they dropped the Natrium and you had unleaded fuel...Of course there was a bottle that spiked the fuel with Natrium to recieve extra protection for the seats/valves but there were absolutely no info that you could/should do that. For most owners of these particular cars everything was just fine, but the once driven hard got eccessive wear just due to the lack of the extra protection. Think about the ZDP (ZDDP) in the oil..makes sense no?

Also keep in mind that the oils of today are validated for newer engines that are constructed with the lower amount of ZDP (ZDDP) in mind.

You could use A 15W-40 diesel oil as the diesels need to have higher amounts of ZDP (ZDDP). The higher viscosity won't hurt anything (this is not the gospel for all engines, but with a Northstar or a 4.5/4.9 it's fine), just you're fuel milage a little bit.

I rather play safe than sorry...

[BodybyFisher]

Hi.

I would certainly use an oil in the SF or SG grades just because of the "right" amount od ZDP (ZDDP). That's what the engine is validated for, try something else than recommended and you'll be the one during the testing...

I once asked the Guru about just these things and though he didn't say it was bad, he said "not so good"...

Things might just work fine with a SL/SM or whatever but keep in mind that the amounts of ZDP has decreased from about 4% to 1/10 of that (if I remember correctly).

And now an example that might make sence to some of you? Here in Sweden when they stopped selling leaded fuel, the public recieved great info about that. The fuel then recieved Natrium as an addtive instead. Everything worked fine when they did that switch (regarding wear on cast iron seats/valves. But then suddenly they dropped the Natrium and you had unleaded fuel...Of course there was a bottle that spiked the fuel with Natrium to recieve extra protection for the seats/valves but there were absolutely no info that you could/should do that. For most owners of these particular cars everything was just fine, but the once driven hard got eccessive wear just due to the lack of the extra protection. Think about the ZDP (ZDDP) in the oil..makes sense no?

Also keep in mind that the oils of today are validated for newer engines that are constructed with the lower amount of ZDP (ZDDP) in mind.

You could use A 15W-40 diesel oil as the diesels need to have higher amounts of ZDP (ZDDP). The higher viscosity won't hurt anything (this is not the gospel for all engines, but with a Northstar or a 4.5/4.9 it's fine), just you're fuel milage a little bit.

I rather play safe than sorry...

I totally agree, I had started the previous thread on ZDDP

[Barry94]

I've been using "Diesel" engine oil in all my vehicles since 1968.

There have been many.

I've never had a failed CAT, or a failed engine in all that time.

I've been using it in the '94 STS since I purchased it, 10 years ago. The head bolt/ gasket failure I

don't attribute it to the type of oil used.

The oil consumption 10 years ago was about 1 liter / 2,500 km, now (at 200,000 km) it's about 1 liter / 5,000 km.

I use Exxon/Esso XD3 (since 1968), in the lawnmower and snow blower as well.

The subject of ZDP gets a lot of discussion on the Corvette sites as well.

Bottom line, in flat tappet engines, you need extra ZDP content, either by using diesel oils or adding EOS.

Barry

[KHE]

I've been using "Diesel" engine oil in all my vehicles since 1968.

There have been many.

I've never had a failed CAT, or a failed engine in all that time.

I've been using it in the '94 STS since I purchased it, 10 years ago. The head bolt/ gasket failure I

don't attribute it to the type of oil used.

The oil consumption 10 years ago was about 1 liter / 2,500 km, now (at 200,000 km) it's about 1 liter / 5,000 km.

I use Exxon/Esso XD3 (since 1968), in the lawnmower and snow blower as well.

The subject of ZDP gets a lot of discussion on the Corvette sites as well.

Bottom line, in flat tappet engines, you need extra ZDP content, either by using diesel oils or adding EOS.

Barry

I noticed that the latest Diesel oils are now rated SM..... to me, that means less ZDP.

[Rich]

I seem to have come across some additional information regarding the reduced levels of ZDDP. The API introduced the SJ standard for motor oils in 1996. This standard already mandated reduced levels of ZDDP. Manufacturers of 1996 and newer automobiles requiring API service grade SJ oils would have needed to certify that their flat tappet cam motors would be adequately protected using these then newer (SJ) ZDDP reduced motor oils. Perhaps the cams and tappets of 1996 and newer N*'s are hardened further than those of pre-1996 N*'s. Following is from www.lnengineering.com:

"In 1996, API introduced the API SJ classification to reduce these levels to 0.10% or less. The latest API SM standard for car oils calls for a zinc and phosphorus content less than 0.08% to reduce sulfur, carbon monoxide, and hydrocarbon emissions. As a result of this mandate, some motor oils now have as little as 0.05% zinc and phosphorus."

The levels of ZDDP in modern API grade SM motor oils are less, but not that much less than what was required by the older SJ grade required in 1996. Perhaps the current levels are fully adequate for 1996 and newer N*'s and maybe simply shortening drain intervals is all that's required for more than adequate protection.

Just a thought.

[Jan Olsson]

Here's a post you might consider?

From the other forum.

"You are correct in assuming that the later API grades such as SL or SM are "better" and , as such, supercede the earlier grades. That is conventional wisdom and is pretty much the case as one of the API requirements is that "improved" performance grades supercede prior grades and are always backwards compatible.

Having said that.....the current crop of oils "rated for gasoline engines" that are on the shelf in the most obvious locations in the stores are also "fuel economy" oils. Any oil with the ILSAC "starburst" symbol that says "for gasoline engines" is a bit of a hybrid....those oils meet the latest API performance specs, have the minimum allowable ZDP (to prevent catalyst contamination) and have friction modifiers in the oil for fuel economy improvement.

The difference is that the API specs just relate to the oil's performance as tested on gasoline engines. API specs have nothing to do with friction modifiers or MINIMUM ZDP levels. The API specs just have minimum performance specifications based on actual engine testing.

Understand that the API performance specs have a lot of requirements besides just "wear protection". Most all of the improvement in the latest grades is in the area of temperature protection. The latest oils will still perform at hotter and hotter engine temperatures. So they are "better" in that the older oils might start to oxidize and give up around 290 degrees F and the latest oils will still function well at 310 or 315 degrees F. They are not "better" in that they give more wear protection.....they just have better high temperature resistence, among other things.

More modern, current production engines are designed to run with the minimum ZDP oils and friction modified oils. Clearances are changed, designs are changed to add roller followers everywhere that are not ZDP dependent for preventing wear, wear surfaces are hardened where necessary, etc.....

Older engines designed for the SF and SG oils that had more ZDP in them are not as well protected against ZDP depleted oils.

So...technically the older engines should be OK with the new SM oils since the SM oils "technically" supercede the older oils and are backwards compatible. But the newer oils probably are " barely" adequate in terms of anti-wear additives such as ZDP. If the engine is perfect inside it will likely be fine. But if the engine is marginal for wear the ZDP depleted oil MIGHT cause a problem and accelerate wear. Certainly you would not want to use the newer ZDP reduced oils for long change intervals in the older engines.

An older 93 Northstar, for instance, has 32 rubbing element tappets (flat tappets) that require much more ZDP for protection against wear than the 2000 and later Northstars with roller tappets.

If you want to be sure your engine has the best wear protection you can do two things. One, use one of the non-"gasoline engine" oils such as the diesel Rotella or Delvac or Delo oils. Those oils have much more anti-wear protection since they are also certified for diesel use. The other thing you can do is to spike the oil you are using with extra ZDP by adding a pint or quart of GM EOS (General Motors Engine Oil Supplement). The EOS is available at any GM parts counter and is sold as an assembly lube. It is basically plain motor oil with a high concentration of ZDP that will fortify any crankcase fill with the extra ZDP desired for more anti-wear protection. It is the only oil "additive" I would ever recommend as it is specifically designed for this purpose.

If you look at the container of Rotella/Delvac/Delo oil you will see in the fine print that it meets all the API diesel performance specs (combinations of the letters CC and CD, etc.) AND it meets the latest gasoline API performance specs such as SL or SM. Now look at the ILSAC "for gasoline engine" oil across the isle in the autoparts store. Read the fine print. It meets the API gasoline SM specs but does NOT meet any of the diesel performance specs. The diesel specific oil is a much "better" product in terms of wear protection if your engine needs it. Diesels have a much greater need for anti-wear protection due to the soot and combustion byproduct contamination of the oil due to the high compression and high cylinder pressures of the diesel engine, so the oils for diesels have to be much better.

I would recommend the Rotella/Delvac/Delo oils for the 93-99 Northstars, personally. The latest ILSAC fuel economy oils are getting very low in ZDP concentration. Fine with the newest engines on the road but not so fine for a 93 Northstar.

You can get the Rotella/Delvac/Delo oils in 10W30 for your engine but they are much harder to find. Check a truck stop or large equipment supplier. If all you can find is the 15W40 version of the Rotella/Delvac/Delo that is fine in the 93 Northstar. The oil is not that much thicker to hurt anything unless you live in the far north and need to cold start at -40.

The other option is to use one of the "severe service" oils marketed by Mobil that are designed for longer change intervals and marketed as such. If you read those bottles you will notice that they also do NOT meet the ILSAC "for gasoline engine" use as they do not have the ILSAC starburst symbol. That is because those oils designed specifically for longer change intervals also have more ZDP in them that excedes the amount allowed for the ILSAC starburst designation.

I would recommend the conventional diesel Rotella/Delvac/Delo oils. I personally use the Delvac (Mobil) in most everything around the house."

[Barry94]

I noticed that the latest Diesel oils are now rated SM..... to me, that means less ZDP.

Here is some additional information posted by Duke Williams on the NCRS site.

"That label is VERY confusing. SM is listed which means it must meet the phosphorous limitation in the SM spec, which limits Zn to about .08 percent, where CI-4s in the past had about 0.12% percent Zn.

The surrogate for ZDDP concentration has traditionally been Zn, but API chose to limit P rather than Zn. I not sure why, but it could be that there are some other additive components that include P. For a given level of ZDDP most oils have Zn and P analyses in the same ballpark.

I've never run across a CI-4 that was labeled SM, but most are labeled SL. Maybe this blend is older stock as API did not allow use of the CJ-4 service category until last October. The use of SM was allowed in late 2005.

Both C and S category oils are now using a boron-based addtive to augment the lower ZDDP concentration. This allows them to pass the anti-wear tests with lower ZDDP, but I don't think these boron-based additives are proven yet in real world service. Only engine teardown and analysis of high mileage accumulation fleets in the next few years will prove their worth in the real world.

Notwithstanding all the above technical and administrative details, the oil you refer to is perfectly okay to use.

It will take some time to sort out all these details. The good news is that if these new HD engine oils are labeled SM, it's okay to use them in new cars without worrying about either catalyst degradation or excess wear.

If newer C-type oils meet SM, that's okay, especially for late model car owners. But it DOES NOT MEAN that an oil labeled only SM meets a C-type spec, so for vintage cars, don't use an oil that does not carry either CJ-4 or CI-4 spec and ignore the accompanying S-specs.

Duke "