Ok,
So I ended up buying a budget tow rig to use for a year or so. The guy I bought it from says he's used synthetic oil since he's had it. I've no reason to doubt him really, but I don't know him from Adam. He also can't provide and records or proof that it is synthetic in it.

In the back of my mind I though, OK, no problem. I'll send in an oil sample and have it analyzed and they can tell me if it's synthetic based or petroleum based.

I call Blackstone Labs and they start telling me all the tests they do on the oil... spectral analysis, flash point.... yada yada yada... on and on. So then I ask them: "If I send you an unknown motor oil, can you tell me if it is synthetic based or not?" They tell me they cannot tell the difference between the two.

??

I'm really sort of shocked with that answer. I specifically asked about the flash point, since I'd assume a synthetic oil would be a bit higher than a petroleum based oil. "No, we can't tell the difference".

Bottom line is, I really hate to put synthetic in this rig if it never really had it before (due to the mileage). Does anyone have any suggestions for how to tell?

If it was me, I wouldn't worry about it at all. If it makes you sleep better use synthetic, but I don't put the stuff in anything I own because IMO it doesn't effect the actual lifespan of the vehicle. In other words, it may make the motor last a few more miles, but it does nothing for the rest of the drivetrain or vehicle.

Go with the Synthetic and don't look back.

Right

Most places that test oil for commercial purposes and have a "mass spectophotometer" can easilly do the test.

They may only do it for industry where an engine is ruined because of an oil related issue.

Lawyers use these places and obtain testimony as well from their expert witnesses.

But for the average guy it is not usually somehting they can/will do...it's all about price.

Ig the Oil's VI is 120 or greater chances it is a GRP IV oil or at least a good GRP III syntetic.I had read this someplace..

I think a few too many people view synthetic oil as this miracle substance that elminates all engine wear. Wrong! I had a Buick V6 that ended up with noisy lifters (probable cam wear) with a very nice, expensive and frequently changed diet of synthetic motor oil.

I'd be looking at the overall condition of the engine - compression, oil consumption, noise. Think of synthetic as more of an insurance policy for extreme conditions, such as heat or cold.

Michael

Actually, I was just trying to avoid ending up with leaks, burning oil, etc etc... which I've seen happen more than once when switching from regular to synthetic on a higher mileage engine.

Good to know. Thanks.

Maybe I could throw some of it in my bilge and see how bad it stains it!

Heres an old trick - take some oil out and pour it cold into a cup to the very top. dino oil will be able to "crown" at the top and synthetic will spill with no oil above the rim.