Got zinc?

[Duke W.]

Re: i still use mobil 1 in the C-6

What does the API label on the bottle say?

If it's for a modern four-stroke cycle diesel it should be CI-4.

Duke

[Duke W.]

Re: Duke when you change to Cl-4

The base stocks for spark and diesel engine oil are similar as are the additives. The difference is that diesel oils have a higher concentration of critical detegent, dispersant, anti-wear (ZDDP), and anti-corrosion additives than API SH oils designed for modern spark ignition engines.

It's not like changing from IAT to OAT antfreeze, where you should do a complete system flush to purge out all the inorganic antifreeze additives.

To switch to CI-4 you just fill it up with CI-4 at the next oil change.

The commonly available 15W-40 CI-4 oils are suitable for cold starts down to about 10F. For colder weather different grades are available. Mineral oil based Chevron Delo 400 is available in 10W, 20, 30, 40, 50, 10W-30, and 15W-40.

Synthetic based Delo 400 is available in 0W-30 and 5W-40. The only difference is sythethic base stock versus mineral oil. The additive package is essentially the same. Synthetic base CI-4 is worthwhile if you start the engine in sub-zero weather and have high mileage accumulation between changes, but for typical vintage Corvette use - mild weather cold starts and annual oil changes with no more than about 5000 miles accumulated annually, the mineral oil version is more than adequate.

Most mineral oil-based motor oils actually have some synthetic bases blended in to meet current anti-oxidation requirements.

If you want to use another brand of CI-4 - Shell Rotella, Mobil Delvac, or whatever, just google to the manufacturers' sites and get the spec sheets as I did for Chevron Delo 400.

Duke

[Duke W.]

Re: i still use mobil 1 in the C-6

I would consider using a synthetic base CI-4 like Chevron Delo 0w-30 or 5W-40.

I have some studies of engine particle generation, and the conclusion is that once an engine is broken in, there is very little particle generation until end of life. The implication was that changing the filter every oil change is uncecessary, however in the case of extended drain intervals I would change the filter with every change, but not more frequently.

One of the problems that I have with synthetic SH oils is that they have about the same additive concentration as mineral base, and since these additives are consumed with use, you have much less additive concentration during the second half of the extended drain interval, say 5-10K miles.

It's probably not an issue with synthetic CI-4 since you are starting out with more additive concentration.

For my driving situations and climate, annual oil/filter changes (less than 5K miles maximum accumulation) with 15W-40 CI-4 is ideal. I've sometimes only accumulated a few hundred miles annually and have been tempted to NOT change the filter, but they're cheap (and I have a big supply), and if you don't change the filter, you don't purge that half-quart of old oil that it contains.

Another option would be to remove the filter, empty it, and reinstall, but two of my cars have "upside down" oil filters and the only way to remove them without spilling is to puncture the top of the case so the oil inside drains down to the pan.

Duke

[Duke W.]

Re: Got zinc?

The concentration of ZDDP in spark ignition motor oils has been reduced over the years, so if you compare the specified zinc concentrations of CI-4 oils with SM, CI-4 wins, usually by a substantial margin.

Motor oils need more zinc to pass CI-4 tests, but I believe there is a limit on zinc concentration for SM (the catalyst degradation concern), and some oils may not need any zinc to pass the SM test. Conversely, most SMs will probably not pass the CI-4 wear test, due to no ZDDP or low ZDDP concentration.

That's why you probably won't see the SM spec on oils that are primarily designed for diesels, but they do meet SL.

Remember that modern spark ignition motor oils are designed for modern engines almost all have O2 sensors and three-way catalysts, and most sliding surfaces in the valvetrain have been replaced with rolling surfaces.

There is no current motor oil specification that specifically applies to vintage, carbureted, non-catalyst engines with lots of sliding surfaces, so it's up to us to look at modern oils and decide what is best for vintage engines.

Duke

[John L.]

Re: Thanks Duke, Great Info *NM*

[Kevin M.]

Re: Got zinc?

Remember this one.

Kevin