From natural to Synthetic, and back again. . .

[y0ne]

I've recently had my oil changed and decided to give synthetic a try. My truck has 70k miles. I came home and researched, and found that it may not be necessary for me to run synthetic, since I don't tow and drive hard much. Is it bad to switch them up over and over?

 

I've also read that going from natural to synthetic after 50k will cause the lubrication built up from natural oil to 'flake' or get scrubbed off and will deposit in filters and valves. Anybody heard of or confirm any of that?

 

THANKS CHEVY BOYS! I appreciate all you help!

[blue2kzr2]

I put 30,000+ miles on my old truck after switching to synthetic. Had 80,000 miles on it at the time. I only got one little leak that was easily and inexpensively repaired. I didn't switch back, and I plan on switching this truck over to Mobil one as soon as it's due for a change, will have 65,000 on it then.

[03Bowtie]

I switched over to Mobil 1 yesterday and at the Pep Boys where I bought the oil, the guy was very adamant about telling me that once I switch, I can't go back to dino oil. So I guess your answer is no, but I'd like to have an in-depth answer as to why. Anyone?

[01Burb]

The wife has a Volvo S60 Turbo that has had synthetic since 500 miles. The dealer put in dino oil by mistake last oil change and offered to take it out and replace it with synthetic. I was stuck for time and spoke to the head mechanic who informed me that it will not harm the car and gave me a coupon for a free oil change next time around.

 

The car only has 20K on it and is well within warranty so if it goes bang I'm covered. I feel the mechanic would have insisted in changing it out if it was a no-no.

 

Maybe a higher mileage vehicle would be different.

[RyanZ71]

I just switched over from Valvoline 10W30 to Mobil-1 Synthetic 10W30 2 weeks ago at my last oil change. My 99 has 82,000 miles and I have not noticed a problem and there have been no leaks as of yet. Go to the FAQ section here: http://www.mobil1.com/index.jsp

[Chad H]

 

My truck had 1500 when I switched to Mobil 1 synthetic. I wont be switching back.

[GM GIMP]

It won't hurt a thing. I've done it a few times with no problems.

[Black02Silverado]

It will not hurt a thing. That was an old tale from the past. Todays oils are blended really well.

 

Switching to synthetic just means that the oil has better cleaning ability over conventional oil. So if your engine was abuse and oil changes never done on a regular schedule the synthetic that was just put in will be doing a lot of extra cleaning over time.

 

There are a few on another other forum that switch just for the winter months to get the benefit out of cold engine starts with synthetic but switch back to regular oil in the summer.

 

Keep a good maintenance schedule on any sound running piece of equipment and you shouldn't have any troubles.

 

Jayman, where are you? They want an indepth explanation here!!!!

[99GMCZ71]

You can buy the synthetic blends, so i don't think it would hurt to switch.

[JayMan]

Sorry been busy the past few days, so here is my take based on +22 years of observation:

 

A new motor receives maximum benefit if switched to a synthetic as quickly as possible. There really is no such thing as a "break in" anymore, though if you're worried then wait until 1,500 miles or so.

 

The regular API/SAE "Starburst" oil certification, based on the SAE J300 test protocols, is remarkably lame. For example: an oil earns a "passing" grade if it thickens 275%, and if 25% boils off during the test. The test technician is allowed to add 6.5 liters of makeup oil to prevent the motor from seizing during the test.

 

It used to be a LOT worse: the oil could thicken +400% and +40% could boil off.

 

Even at 275%, I doubt the oil would even drain out with the drain plug off. Maybe a hammer and chisle ...

 

In contrast, the European ACEA specs limit oil thickening to 50% and boil-off to 15%. The test technician can NOT add oil during the test.

 

Unless you change the oil VERY frequently, you will experience the following:

 

You will have sludge in the valvetrain, which will dissolve old-fashioned cork gaskets. There will be carbon/varnish on rotating seals like the rear main. There will be varnish/carbon in the ring lands. In the case of rotating seal surfaces, the abrasive carbon/varnish will wear down the seal, but then a neat thing happens: those deposits become your new seal, so it won't leak.

 

 

These deposits can take as little as 5,000 miles to as much as +75,000 miles to form, depending on how the motor is driven. Town stop-n-go is the worst, constant Interstate 75 MPH is the best for any motor regarding longitivity and deposit formation.

 

Synthetics have MUCH higher detergent levels than regular motor oils. This is due to how regular oils and synthetics are made: a regular 5W-30 starts out as a 5W basestock, and the chemical engineers add a lot of polymeric agents to "thicken" the oil so it has accepteble high temp viscosity. You can't use too many detergents or the polymeric compounds will separate from the oil and/or break down, leaving a polymer sludge in the motor and a light 5W to "protect" your motor.

 

Non-synthetic oils are "non Newtonian" oils. That is, due to the polymeric compounds added, which is reflected in the higher VI number, the viscosity is dependent on the shear rate experienced by the oil. High shear forces can be found along the rings when they are scraping past the liner or cylinder surface, and in a diesel with HEUI, where oil is used to pump the injector, there are extremely high shear forces.

 

The repeated exposure to very high shear forces causes the polymeric compounds to uncoil and fall apart. This is a permanent loss of the polymer, since once it uncoils it stays that way. Which is why it's so important to have frequent oil changes when running a regular motor oil.

 

Note that "straight" oils, such as SAE 30 or SAE 40, are quite stable. Their response to shear is predictable and doesn't permanently degrade the oil. They also only work best in a narrow temperature range.

 

Synthetics are derived from esters and polyalphaolephins (PAO) compounds. These are typically organic and inorganic acids. Their structure is free from petroleum waxes and are quite stable. Although some polymers are needed for wide cross-grading, most synthetics are completely shear stable.

 

Since they are so stable, you can really load up on detergents. The primary benefit of detergents is to keep sludge/varnish/ carbon deposits from building up. In HD diesel motors, the detergents help keep the high soot loads from sticking to ring land and turbo bearing housings.

 

It has been my experience that if you switch a high milage motor to a synthetic without doing a "flush" you will experience leaks: rear main, valve seals, and older cork valvecover gaskets. The detegents dissolve the deposits and your ruined seals will seep. Note that most newer gasket materials resist deposit formation and high detergent loads.

 

I've seen HD diesel motors with +120,000 miles switched to Delvac 1 and the soot was knocked loose, plugging the filters and requiring freqent filter changes till things calmed down. Most older gas motors have rear main and valvecover problems.

 

The nice thing about modern technology is that most larger shops can afford a fiber optic inspection scope: you take the oil fill cap off and poke the fiber bundle into the motor or valvecover. What looks clean on the outside is a shock when you see the deposits on the inside.

 

So you have to carefully weight the benefits and disadvantages. If the motor appears to be tight and leak free, maybe it might work. Some folks around here have used synthetics in winter for the cold pumping performance then have switched to a regular for summer, with no problems. This was done from new though.