Hey guys I have a question for you oil experts,

I used mineral oil all through break-in and up to 5,000 miles
with regular oil changes, etc.

At 5,000 I switched to synthetic oil

So, I just recently decided to have my oil changed at my
7,500 mile maintenance - well, without getting into
detail I'm pretty sure they switched me BACK to mineral
oil by mistake...

so my question is: will going from mineral to synthetic
and then BACK to mineral damage my engine?

<font color=red>..</font color=red> 2004 Black 6-Speed <font color=red>..</font color=red>

 

GM (as in Chevy) advised me that once I switch to synth in my '96 Impala SS, that I can't switch back. They say that the synth causes the seals to swell slightly, and once you switch back, the seals tend to go back to the normal size. This causes gaps and allows more oil to get into places it doesn't belong.

F.Y.A.

 

There are a lot of myths about synthetic oils out there. Although I'm not an oil expert, I have done a lot of reading and talking to oil experts and I've used synthetics in several cars and motorcycles.

Sythetic oils are made from the same dino-juice crude stocks as "conventional" oils. The word "synthetic" is kind of a misnomer as they do come out of the ground and are not really "man made". They are subjected to more advanced processing techniques to eliminate virutally all the undesireable "long chain" hydrocarbon molecules. These long chains are the ones that are the basis for asphalt and plastic precursors that come out of crude oil processing at refineries. They are considered "contaminants" in a motor oil as they contribute to high viscosity at low temps and sludge and other byproducts from high temp operation. Think of synthetics as "ultrapure" motor oil and you have a better idea of what they really are. Or think in terms of "virgin" and "extra virgin" olive oils - an indication of purity and quality.

That said, they also have special additives to even further enhance low and high temp operations, wear, etc.. The first uses for "synthetic" lubricants was wheel bearing grease for WW2 carrier planes (according to the Mobil 1 website). They had lots of failures from frozen wheel bearing grease when landing after cold, hi altitude flying. All space shuttle flights depend on synthetic lubricants to prevent freezing in the extreme cold of space.

According to the major synthethic oil makers (Mobil, Quaker State, et al), all synthetic oils are 100% approved by all car manufacturers for use even in new engines. Did you know that Mercedes has put Mobil 1 in engines at the factory since about 2000?? (There goes the "can't use them for new engine break-in" myth)

There really is no basis in fact for these myths about seal swelling and shrinking. I've never seen anybody provide evidence of this even in some pretty heated chat room discussions of Harley owners when talking about synthetic oils (I am Harley rider and I do use synthetic oil and I don't see leaks, but that's a data point of "one", so don't believe me alone).

I'd suggest reading the FAQs on the synthethic oil manufacturer's sites to get more insight and less myth.

-- Kevin Talbot (Seattle)
2004 G35/5at/Diamond Graphite/Graphite leather/Premium pkg/Nav/18" wheels