BB 1970 Changing to syntetic oil

[Markus 38206]

What's the opinion of you experts regarding change to full-syntetic oil for a completely rebuild engine 454 from 1970? I have heard it would be good to start after rebuild with mineral oil and then change after about 2000 miles to syntetic one. It's a high performance engine (max rpm 7000)and therefore syntetic high quality oil (like mobil 1) seams as a good choice to me. What do you think?

[Michael W.]

Re: BB 1970 Changing to syntetic oil

Empirical evidence infers that it might someday prove to be just as good as dino oil.

You'll gain little or nothing over standard type oils, so why bother?

[Terry F.]

Re: BB 1970 Changing to syntetic oil

In theory, it should be superior to standard motor oils. I don't know what evidence you are talking about though.

[Chas Kingston]

Re: BB 1970 Changing to syntetic oil

Back in the mid-70s, when I was a crewman on a Can-Am car, out car owner was having an engine overhauled at the factory. He had them dyno-test it twice; once with Mobil 1; the other time with Valvoline Racing Oil. The dyno results were identical.

Ol' Geezer

[Richard D.]

Re: BB 1970 Changing to syntetic oil

Would not hurt, and after all, how much extra is it gonna cost assuming you're going to do one change per year or so?

If you run into an overheat situation, it would protect your engine better than petro based.

Rich

[Duke W.]

Re: BB 1970 Changing to syntetic oil

You should check the archives as there is a lot of discussion on this subject.

The best motor oil for vintage engines is HD diesel engine oil, API service catergory CI-4.

The reasons and been put forth and discussed a zillion times.

Duke

[Terry F.]

Re: BB 1970 Changing to syntetic oil

I forgot the technical terminology, but because synthetic motor oil has more uniformity of the size and shape of the molecular structures I believe it forms a stronger hydrodynamic wedge when pumped under pressure between two moving surfaces. Because of the consistancy of molecular size and shape it takes on other characteristics as well which are favorable to engine wear. But, they also have a lot of similarities to standard motor oil. If you are the type of person that does not keep there car for more than 3 to 5 years, you would probably never benefit from using synthetic. Synthetics are shown to be more stable over time with heat cycles and temperature extremes so they outlast conventional oils. Just my 2 cents.

[Michael W.]

Re: BB 1970 Changing to syntetic oil

That's one of the dozens of nice theories that circulate, but my 25 years of real life experience in the aerospace industry helping monitor a fleet of 40K+ engines from cradle to grave says there's no difference.

Got any real life proof to back up your theories?

I guess the synthetic oil legend is much like UFOs or Big Foot. There's thousands that either claim it's true, or just want to believe that it's true but can never quite come up with the goods.

And no, I don't flip my cars every three-five years. My 'newest' car is a 1993. I was going to trade it in this summer when it hits 250,000 Km, but it's still running like new, so I won't bother.

[Duke W.]

Re: BB 1970 Changing to syntetic oil

It's utterly amazing that my SWC ran its 115K mile first life in the sixties and seventies on the "heavy duty" detergent type 10W-30 oils of that era, and when I tore it down the crankshaft miked right in the middle of the OE dimension range and the bearings showed no visible wear. There was three to five thou taper at the tops of the cylinder bores, but no other significant wear of any kind including the ol' Duntov cam lobes.

Modern mineral oil based API SL motor oils for spark ignition engines are better in terms of both oxidation resistance and additive package, and the mineral oil based CI-4 HD diesel engine oils are better than the modern SL oils and vastly better than the detergent motor oils from the sixties.

Synthetics are great for extended oil intervals, especially if the car has an oil monitoring system like modern Corvette that will let you go up to 15K miles, but keep in mind that GM still requires that the oil be changed annually to maintain warranty coverage, regardless of mileage. Synthetics are also great if you have to start your engine at 20 below zero or lower because some blends (5W-30 and 0W-40) have a lower pour point than mineral oil based motor oils.

Since most vintage Corvettes only see a few hundred to the few thousand miles annually - usually in mild to warm weather - an annual oil change with a CI-4 oil will give you the best detergent and dispersant package, along with the best protection against wear and corrosion due to their high dose of anti-wear and anti corrosion additives than any SL oil regardless of the base - synthetic or mineral oil

It's interesting how in all these endless arguments about synthetic versus mineral oil you almost NEVER hear any discussion about additive packages in the various types of oil. This is the most important issue but 99 out of 100 or maybe even 999 out of 1000 are clueless.

Duke

[Duke W.]

PS

I want to emphasize the lack of wear on the crankshaft and bearings of my engine. These are areas that are subject to full hydrodynamic lubrication under all operating conditions except maybe starting. The bottom line is that virtually any oil will provide adequate hydrodynamic lubrication. Vegtable oil will do the job, but it won't last long because it oxidizes more rapidly than any modern motor oil.

The problem areas are always were you have "boundary lubrication". This occurs at the top of the cylinders when the rings slow, come to a full stop, and reverse, and this is why you nearly always see taper at the top of a bore, even though everything else might show virtually no wear.

Cam lobes can also be subject to boundary lubrication, especially if the engine has high force valve springs.

It's the boundary lubrication problem areas where the HD diesel engine oils will pay dividends with their increased concentration of ZDDP. This chemical goes into action when there is metal to metal contact and will reduce the incidencce of bore taper and piston/wall scuffing.

Finally, since most of our freshly rebuilt engines will likely never "wear out" due to use, long term corrosion becomes an issue, and the richer corrosion inhibitor package in the CI-4 oils (diesel blowby is much more corrosive than gasoline engine blowby) will provide better long term protection against the effects of corrosion.

Duke

[Terry F.]

Re: PS

From what I have read, I think the big advantage of a synthetic would probably be the interval change period. Also, there may be some greater flow characteristics at low temps. From what I have read, most wear occurs at start up when acidic gases and chemicals hit the bare metal surface, not from friction. I was surprised to find that out. My understanding is that better oils can absorb these chemicals more effectively. It is also my understanding that better oils keep dirt suspended in the oil without depositing it on the metal surfaces in the form of varnish, etc. Oils that have a narrow viscosity range 10w30 versu 10w40 tend to be less volitile when subjected to increased temperature and hold up longer. Synthetics have been shown to hold up superiorly in temperature extremes and break down slower. But, that may be something that most engines under normal operating conditions never fully benefit from. The idea of using diesel engine oil in an older style engine does sound good because they come with the extra detergent package and wear package. The reason they need that is because diesel fuel is less refined compared to gasoline. As a result, the oil accumulates the residues from combustion much faster. Just my understanding of things, not an engineer or anything. Just trying to add to the discussion. Thanks, Terry

[Dick W.]

Re: BB 1970 Changing to syntetic oil

My two cents worth:D Synthetic is wonderful, but an older big block does not have the modern sealing components in place to keep the oil in the engine. Synthetic will invent a place to leak. An I always say that a Chevrolet V-8 that does not leak oil has no oil in it...:D

[Duke W.]

Re: PS

Terry - everthing you mentioned except for oxidation resistance (higher oxidation resistance increases the potential change interval) and low temperature flow characteristics are a function of the additive package, not the base stock.

That's why I keep harping about additive packages as the key characteristic of a motor oil, not the bast stock. Most of us only drive our vintage Corvettes a few hundred to a few thousand miles per year, so the longer potential life of synthetics is of little value because we should change the oil any least one a year regardless of mileage, and I don't think any of us start start our Corvettes in sub-zero weather.

Duke

[Terry F.]

Re: PS

Thanks for the information Duke. Best regards to everyone, Terry

[Joe L.]

Re: BB 1970 Changing to syntetic oil

Mike------

I thought that aircraft turbine engines used synthetic oil exclusively.