Oh no! more oil questioss

[frank mccracken]

I am convinced in my little mind that I NEED to use Mobil 1 synthetic oil but thanks to this board I understand the need for the additives in deisel oil. Talking to the Mobil 1 tech line I am informed that synthetic "Delvac 5w40" is exactly the same as "5w40 turbo deisel truck". The regular 5w40 is not available in my area but the Delvac is but it seems much more expensive. I checked the archives and was not able to find if this has been discussed. If it has could someone please provide me with a link?

[lyndon sharpton]

Re: Oh no! more oil questioss

just use the Mobil Delvac 1300.

[Duke W.]

Re: Oh no! more oil questioss

The PRIMARY advantage of synthetic base stock is greater resistance to oxidation, so a synthetic base is appropriate for engines that run VERY HIGH oil temperature or is suitable for extended drain intervals.

A second advantage is wider viscosity range with little or no VI improvers, which tend to break down with temperature/time.

Within the same viscosity range and operating temperartures, synthetics are NOT "more slippery" and WILL NOT reduce internal engine friction. Those are MYTHS!

So a synthetic base CI-4 ends up at 5W-40 and is suitable for ambient cold starts down to about -20F, where a mineral oil base stock ends up at 15W-40 and is only suitable down to +10F cold starts.

Most vintage Corvette engines don't run excessively high normal oil temperature, and since most vintage Corvette owners don't usually do cold starts below 10F and don't see high annual mileage accumulation, there is no benefit from the additional cost of synthetic base oils, and an annual oil change with a mineral based 15W-40 CI-4 oil provides the best protection at the lowest cost.

One other tidbit is that the current oxidation requirements for CI-4 oil cannot be met with only refined mineral oil stocks, so the basic "non-synthetic" CI-4 oils have some synthetics blended in to pass the oxidation tests, and this also reduces or eliminates the need for VI improver to gain their multiviscosity ratings.

Duke

[Paul L.]

OK Since We are Re-visiting

The additive thing. Can a dose of GM EOS with regualar modern non-synthetic oil replace the zinc deficiency?

[Duke W.]

Re: OK Since We are Re-visiting

EOS is not cheap, and GM only recommends it for engine breakin.

My question to you is: Why not just use CI-4, which has plenty of ZDDP, instead of screwing around with additives and SM oil?

Duke

[Dennis B.]

Re: OK Since We are Re-visiting

Duke,

You continue to show the utmost patience with people and this topic. I get the message. Lead on Duke, lead on.

[Duke W.]

It ain't rocket science...

There are three requirements for a motor oil.

First. Select a viscosity range that is suitable for the anticipated range of cold start temperatures that you expect over the time period that the oil will be in the sump. Owners' manuals and service manuals have charts, which makes this selection almost a no-brainer.

Second. Select an oil with an additive package that is suitable for the engine. The additive package is BY FAR more important than base stock because all modern base stocks are good. Vintage engines have more sliding surfaces than modern engines, and because some additives, including the very important ZDDP antiwear additive, have been reduced in current spark ignition engine oils (there is concern that combustion byproducts may degrade catalysts), API SM oil is NOT the best of available choices for vintage engines. Modern spark ignition engine oils are designed for MODERN, not vintage, engines.

But it so happens that no such additive limitations exist in the diesel world (at least for now, but change may be on the horizon). A modern CI-4 oil designed for modern diesel engines is BEST for vintage spark ignition engines because current diesel engine oils have a greater concentration or detergents, dispersants, anti-corrosion, and anti-wear additives than modern spark ignition engine oils.

Third. Choose a base stock that is suitable for your driving environment. High oil temperatures (like road racing without an oil cooler) or extended change intervals benefit from the higher oxidation resistance of synthetics. Or if you like to winter in Fairbanks and summer in Miami, a synthetic 5W-40 CI-4 would be a good year round choice, and it should have enough service life to make the round trip up and back on the AlCan highway. Such a wide viscosity range is not possible with mineral based oils without the addition of excess VI improver, which breaks down with use.

For the rest of our vintage cars, a mineral oil based 15W-40 CI-4 is suitable for cold starts down to about 10F and ambient temperature to 100+ and has a service life of 5000-7500 miles or one year, whichever comes first.

If you want to learn more about API service categories for motor oil, go to:

www.api.org Click in your garage...

Duke

[frank mccracken]

Re: Oh no! more oil questions

Thanks AGAIN fella's. I like the synthetics pourability at colder temps and at startup. Plus I like the extended oil change intervals, sometimes I don't change my oil when I should after lots of miles in the summer. I'm goin' with the delvac synthetic. Just makin' sure I'm using the best oil within those parameters.