Change in oil additives?

[Roy S.]

[Kevin M.]

Re: Change in oil additives?

I'm sure Duke has mentioned this, I'm sure he'll let us know.

Kevin

[Bill Lacy]

Re: Change in oil additives?

Roy
I have been running Rotella T 15w40 in my 435 for about 3 years and have had no trouble? No trouble with it in my Duramax.P.S. still no driveline in St Louis? Bill

[Mike S.]

Re: Change in oil additives?

Duke has posted information about this several times. As a result, I switched to diesel grade oil in my '66 last year.

I believe it was the zinc additives that were dropped.

[Joe L.]

Re: Change in oil additives?

Roy-----

Basically, I think that you've gotten the straight story. However, modern S-prefix engine oils are rated for all gasoline engine service, INCLUDING engines with flat tappet cams, so I really hate to question the judgement of the manufacturers or the SAE and API. Those oils should work ok for all gasoline engines.

Notwithstanding the above, there are 2 factors here, for sure. First, camshaft break-in for a flat tappet camshaft is a VERY critical period in the life of the camshaft and the engine. GM has for many years recommended the use of EOS both during assembly and as an additive during engine break-in. I would not dream of perfoming initial engine operation and camshaft break-in without a can of EOS in the oil. I would do this even for roller cam engines.

The second factor is that the zinc-based, EP (extreme pressure) additives in modern oils have been reduced greatly. There's no question about that, even though the oils are still rated for all gasoline engine service. For older type engines, the loss of the zinc additives, regardless of what their function has been replaced by, is "not a good thing".

So, for older engines, especially those with flat tappet cams, I think that the use of a C prefix diesel engine oil might be a very good thing to do. These oils do have FAR higher concenrtrations of the zinc-based EP additives. They are also fully rated and approved for gasoline engines as they are dual-rated with the S-prefix gasoline engine oil rating. So, they are fully approved for use in any gasoline engine.

[John H.]

Re: Change in oil additives?

Roy, that's correct - the current passenger car oil formulations have backed out essentially all of the zinc anti-wear additive (ZDDP) they had in the past, as it poisons catalytic converters. Diesel oils meeting the API CI-4 spec (Shell Rotella, Mobil Delvac, etc.) have an additive package containing a high level of ZDDP, and are better for rubbing-wear surfaces.

[John H.]

Re: Change in oil additives?

Interesting trivia - my Chapter toured the GM Performance Build Center yesterday (where they hand-build the Corvette LS-7 and Cadillac supercharged Northstar engines), and they use "Lubrizol" exclusively as their assembly lube for every part in the engine. Lubrizol has been around for decades.

[Duke W.]

Re: Change in oil additives?

Subject has been discussed extensively (archives).

I recommend API CI-4 HD diesel engine oil for all vintage engines, and I'm even switching my "modern" (1988 MBZ, 1991 MR2) catalyst cars to CI-4.

Even if I had a new car, I would be concerned about the new SM spec oil. Catalysts are cheaper than major engine work, and new cars usually have very low oil consumption, so catalyst degradation due to the combustion byproducts of ZDDP, if any, will be slow.

GM EOS has a high dose of ZDDP, but it's only necessary for break-in if you use CI-4.

Duke

[Joe L.]

Re: Change in oil additives?

John------

Yes, it has. Also, I think that it's very possible that GM's EOS is Lubrizol or a Lubrizol-manufactured product in a GM-labeled can . Certainly, GM does not actually make this product and it has also been around for a LONG time.

[Michael H.]

Re: Change in oil additives?

Duke,

Can Cl-4 be mixed with conventional S motor oil? Just curious. I like the lighter weight available in conventional oil but would also like to get the benefits of the additive package you speak of in Cl-4. Reading your posts on oil for the last year or so has convinced me beyond doubt that I should at least have some of the additives mentioned.

I suppose the Cl-4 would be ok for the big block car but I would like to use a lighter viscosity in my SB car.

[Duke W.]

Re: Change in oil additives?

Mixing is not a problem, CI-4 with S-rated, and most synthetic bases are compatible with most mineral oil bases.

In fact, most conventional mineral oil bases need a small does of synthetic to meet the current oxidation requirements.

The additives in all motor oils are essentially the same "stuff". It's just that CI-4 has some additives, like ZDDP, in greater concentration. I believe some of the new SM oils have NO ZDDP, which is not good for a vintage engine.

The common 15W-40 CI-4s are okay for cold starts down to 10F, and should be fine for year round driving in mild climates or the normal driving season if you store your Corvette during the coldest winter months.

Duke

[Michael H.]

Re: Change in oil additives?

Thanks Duke. That's exactly what I needed to know. The 66 BB will get a full load of Rotella. I may mix 50/50 in the 63.

I questioned most of the discussion on this oil last year but I'm now 100% convinced that you are on the money with this. Old habits are difficult to change.

[mike mccagh]

Re: Change in oil additives?

john, duke, joe, mike: when you guys mention the Zinc "poisons" the cats, does the end product of the contamination actually reduce exhaust flow thru the cats or does the Zinc simply render the catalyst impotent? I've been running Esso diesel oil in all my vehicle since the mid 70's, most of which lack cats, but i worry about our LT5's that do have cats. i've heard of cases of the left cat becoming blocked to the point of heating and destroying the left head on a LT5. I recently "lost" the contents of the cats on the 61 Farm Use vette as it's been exposed to some pretty hash usage during motorsport activities and i didn't want to risk cookiing a LT5 head.Loosing the contents is a relatily easy chore. mike

[Duke W.]

Re: Change in oil additives?

I think it's a combination of both chemical poisioning and actual mechanical blockage. The substrate matrix can also fail due to thermal fatigue, but this is purely a thermal-mechanical failure not related to combustion byproducts.

ZDDP combustion byproducts can also foul spark plugs, which is why GM only recommends EOS for engine breakin.

The problems would obviously be exacerbated by high oil consumption, so if oil consumption is "low" - say a quart in no more than 2K miles, I don't think the extra ZDDP in CI-4 is going to cause any problems - at least in the short run.

Catalysts all degrade from age - thermal cycles, oil additive byproducts, and some other issues. Excess richness from inoperative O2 sensors can render catalysts ineffective, but correcting the rich condition and some good thermal cycles will usually bring them back to life. Catalyst aging is a complicated issue with multiple issues in varying degree that are not fully understood, but, like I said, if oil consumption is not high, I don't think ZDDP is going to harm the catalyst anytime soon.

Duke

[Joe L.]

Re: Change in oil additives?

mike-----

I think that the main effect of the zinc is a reduction in the effectiveness of the converter rather than physical plugging. Plus, I really don't think that the zinc is as "bad an actor" in this regard as we might be lead to believe. I think it's more a case of many modern engines not really needing the EP additives and the fact that they produce some converter degradation. So, "conventional wisdom" probably dictates their elimination or reduction in mass-market oils.

Keep in mind, though, as I previously mentioned: the current diesel oils ARE dual-rated for both diesel and gasoline engine service. So, they are fully approved for use in all gasoline engines, including those with catalytic converters. The problem is that most of these oils that are widely available are sold only in the popular viscosities for the "diesel guys". These are not approved for modern gasoline engines and, obviously, would be a problem for someone with an engine under warranty. I do understand, though, that these diesel oils are available in 10W-30 weight if you look for/order it. In this case, the oil would be fully approved for use in modern gasoline engines since it would have both an S-prefix service rating as well as an approved viscosity.

The catalytic converters on an LT5 might not be as easy to "lose the contents of" as one might think. These are a MONOLITHIC type converter, as are most modern converters. You can't just "pour the beads" out of them. You would have to cut open the converter, extract the monolithic element, and weld the converter back up again.