Using old oil OK

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Dec 15, 2008
Lakewood, CO
I've got a case of 20w50 Golden specto, and a case of Castrol GTX 20w50 both from around 1990 with SG rating. I'd like to get rid of this oil. My motorcycles are 1978 era so SG should be ample? Also 20w50 is a little thick, would mixing a quart of 10w30 to 2 quarts of this old stuff be advisable? Or should I just throw it away?
20w-50 should be fine for your motorcycles. That's what is recommended for my 1975 Honda 750 as a warm weather oil. 10w-40 is the cold weather recommended. But if you are running a Harley of that era, it's probably a heavy straight weight that should be used.
I'd be more afraid of sliow-kinetic oxidation and falling out/destabilization of additives. Id use it as a top-up oil, and/or as a flush, but Id not want to use it as a full-up lube oil for regular service, even in a seldom used machine.
I'd be more afraid of slow-kinetic oxidation

What does that mean?
What is the slow-kinetic oxidation rate as a function of time? I don't think the additives falling out is going to be a problem after you put it into the engine and run it.
slow-kinetics being what happens at ambient conditions... Obviously oxidation can occur at some rate when at elevated temperatures in the engine... But exposed to ambient conditions, there will still be some oxidation rate...

Older oils sometimes had less stable forms of additives. The additives can loose their performance.

There were some good discussions on this years ago... I couldnt find some of the older ones, but here are two and show that there is a concensus but some folks are finding longer life (potentially).
I have yet to find a documented case of vintage oil failed in an engine that it was designed for. I still have a case of Motul 15w50 that I bought back in 1992 for my CBR900RR. May be I should send it in for a VOA and see if any thing is missing. I have been using this vintage oil off and on for the past 17 years in several bikes with no problem. I still have leftover Red Line oil from late 80's that I am still using in my 87' Supra Turbo.
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