Switching motor oil from synthetic to conventional

[rayra]

I think the only real relevance of the 'synthetic vs normal' oil question is regarding how hard the motor is run, for how long, and how precision a machine it is in the first place. A high-rpm small-liter turbo-charged racetrack motor, synthetic all the way. An old domestic V-8 putting down a trail, no need for it.

 

[Longrange308]

I personally have always run synthetic, unless Im breaking in a new engine. I use either Amsoil or Pennsoil Synthetic Platinum, and run it for a full year. 10k-12k miles later, it is drained and replenished. Blackstone indicates no issues and after doing filter dissections, I have never found anything worrisome.

You can do conventional oil changes every 3k, but you aren't saving money.

and FWIW, a lot of oils out there are blended from synthetic and conventional base oils. They work just fine, and you should have no issues blending, mixing or swapping between synthetic and conventional.

 

[RocKrawler]

Synthetic is better at cleaning, and is thinner.

Nope. Viscosity is equal between conventional and synthetic, 30 weight is 30 weight. One is not "thinner" than another IN THE SAME VISCOSITY. So although they MAKE the oil in thinner viscosities, (such as a range beginning in a zero weight) 10/30 synthetic is the same as 10/30 conventional viscosity wise.

From Marlin Davis, Car Craft Magazine Engine Editor:

Because a synthetic oil is chemically produced, there are no contaminants in the oil. By contrast, conventional oils contain small amounts of sulfur, wax, and asphaltic material that can promote detonation as well as varnish and sludge buildup. With no wax, synthetics will flow at much lower temperatures than conventional oils. In fact, synthetic oils are now available with viscosity ratings as low as 0W-30, as in Mobil 1's new Tri-Synthetic blend or Castrol Formula SLX. These oils flow more than seven times faster than a conventional 5W-30 motor oil during initial start-up, yet at normal operating temperatures act like a regular Grade 30 oil.

An 0W-30 synthetic oil is capable of pumping easily at -62 degrees F and flowing at even lower temperatures. Conventional oils are essentially frozen solid at that temperature, so there's simply no conventional equivalent to this new grade. There are 5W-30 conventional and synthetic oils, but even here, the synthetic has a real-world advantage: Mobil 1's 5W-30 will pump at -58-degrees F, compared to about -35-degrees F for a conventional oil.



Read more: http://www.hotrod.com/how-to/engine/synthetic-vs-conventional-oil/#ixzz3b9tXK09I
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[153624]

Some of you will read that article and scoff to yourselves who really cares about those kinds of temperatures....... I Do!!! It routinely gets that cold where I live and work in northern Canada. Not in the arctic by any means but -40c at times every winter.

In the past I have run 0w40 all year round. Or have changed up to 5w40 sometimes in the summer.

The difference 0w40 makes at those temps is literally the difference between starting your engine and not having it turn over at all.

 

[Stumpalump]

Oil companies have oil engineering labs. The guys with the white coats. I figured out a way to call them directly instead of talking to a marketing team so I called most of them a few years ago. It took me a few days to pick their brains. I won't proclaim I'm an expert but after talking to them you can and should take these few points to the bank. Two stroke oils and even tc3 water cooled outboard engine oil are backwards compatible for air cooled engines or basically all two stroke oil is good for all two strokes today. In older engines like 4.0 Jeeps or anything with a flat tapped cam you have one best choice 15w50 synthetic. Year round, for any engine below the arctic circle. Once you drop to the minus 40's and such you run 15w50 with a quart or two of 0w30 mixed in. Dino oil sucks but if you also like bias ply tires then as everybody knows buy one of the blends for diesel trucks. A good reason diesel or synthetic oil is better zink. They put more zink in diesel oils and in synthetic. They can legally put more in synthetic because the change interval is allowed to be extended. Zink gets used up so the more you start with the longer you can run it. That's the bottom line on zink. The amount of zink is regulated by big brother. Reason enough to buy diesel or synthetic but the best reason is that if you blow a radiator hose, don't notice an over heat condition or run low on oil the synthetic will protect way longer. So if there is one best reason it's to prevent failure in an abnormal condition. Newer engines spec thin oil for gas mileage. Run synthetic oil rated for the highest outside temps in your owners manual year round. I'll leave it at that. PM me if you want numbers for the labs and can be creative enough to get info out of them with BS or intelligence.

 

[JPsLC]

Stump, the offer to call the labs is tempting due to the possible entertainment value it offers, but I don't have the time. Maybe in the future.

I had decided to stick with synthetic oil for the reasons given by all who commented (thanks again!), and statements in the article RocKrawler posted affirm my decision, i.e., Because a synthetic oil is chemically produced, there are no contaminants in the oil, ...synthetics will flow at much lower temperatures than conventional oils. ...these oils flow more than seven times faster than a conventional 5W-30 motor oil during initial start-up.

I firmly believe the 4.0L in my Jeep still runs great and doesn't burn oil at 265,000 miles because I always allowed it to get to operating temperature before driving it hard and bringing the rpm's up for highway driving (who cares that it has the 0331 cast head and exhaust manifold that both should have cracked before it left the lot). This could have been easier and happened faster using a synthetic oil, but it obviously works with an understanding of what the conventional oil and old motor need.