Here are the highlights:
I am about to install all new parts, including brass syncrho rings, into a Borg-Warner 4-speed. The potential corrosion of such brass parts by gear oils has been mentioned on our forum a few times over the years. It is widely discussed on the WWW where its severity is generally, IMHO, very overstated for modern gear oils. The test for corrosion of such yellow metals (those that contain copper) are not done using brass but with bare copper which is more easily damaged. At least in the USA, the test normally used is ASTM’s D-130, Copper Strip Tarnish Test. The results of this test are normally reported on the Technical Data Sheet of any oil you might want to use, that is provided you can find the TDS.
Since I was trained years ago by the US Army as a petroleum lab tech I conveniently have a set of the ASTM standards which include this test. I couldn’t find a data sheet for the oil on my shelf although on the jug it says ‘Protects against the corrosion…of copper…’. Other than 80W-90, no other ratings are on the bottle except GL-5. As a demonstration to myself I decided to run a psudo-D-130 test on the Super Tech GL-5 80W-90, EP gear oil just to see what happened. Some of you might be interested in the results. I can’t duplicate the required temperature stability of 1 degree Celsius or a few of the other details so its not a true D-130. I also don’t know that the Alfa Romeo copper oil plug washer I used is 99.9% pure copper as specified. But the test is about as close as most of us could achieve in our own kitchens and I doubt that its far from what an official D-130 test would show.
This test calls for a mechanically cleaned, bare copper strip to be immersed in the test fluid at 212 F for 3 hours and the change in color of the copper strip is compared to an official chart. The darker the strip, the more corrosive the fluid, i.e. oil in this case. The chart is a visual aid to better define the numeric classifications which range from 1 (slight tarnish) to 4 (corrosion). Not having a chart, I have to rely upon the descriptive words for the various categories which range from 1a (Light orange, almost the same as fresh polished strip) to 4c (Glossy or jet black). Just for kicks I also threw a new syncrho ring in with the copper washer.
I heated the oil in a 2-qt sauce pan and monitored surface temperature with a calibrated IR gun (with emissivity adjusted to 0.95) as well as mechanical, liquid and electronic immersion cooking thermometers some of which proved quite inaccurate. Even the lowest simmer setting of the gas flame was too much for 212F so I had to cycle the burner on 5 min, off 2 min, such that the oil temp cycled between 205-220F after an initial spike to near 235 F. If anything, I would say that I exceeded the specified temperature and should have more corrosion than an ‘official’ test would produce.
The attached test results picture taken in afternoon sunlight shows the synchro ring and copper washer with the washer’s left side re-polished after the test. The left side of the copper and the 2nd synchro ring are included as a indicators of ‘before’ colors. I don’t have to tell you which is the tested brass ring since, as expected, the rings look identical (its on the left). The copper is definitely not Claret red (2a) not even Dark orange (1b) but I would classify it as 1a (Light orange) which is the lowest rating available. Typical gear oil tests allow at least a 2a if not a 3 rating. (I have never seen a modern, tested gear oil data sheet that reported a 3 rating even if it might have once been allowed. The latest MIL-PRF-2105E from 1995 only allowed 2a.)
Am I saying that all EP gear oils are perfectly safe for all applications? Not at all. But this test reaffirms my belief that potential hazards of GL-5 rated EP oils are often greatly exaggerated. Even this cheapest of gear oils tests perfectly fine in terms of copper corrosion. If you are concerned about some oil you might want to use either check the data sheet or perform your own D-130 test as I did.
Yes, this thread is about GEAR oil specifications, particularly the GL-5 specification. 50 years ago before the GL ratings were being used such an oil would have been called EP (Extreme Pressure) which explains the title of the thread. Such oil is not necessarily limited to manual transmissions but would/could also include oil for differentials, steering gears, etc. Motor oils use entirely different wear additives and ratings.
You will find that nearly ALL petroleum products have a copper corrosion test as part of their specifications. Even petrol has to pass that kind of a test. Of the various POL products (Army-speak for Petroleum, Oil and Lubricants) GL-5 gear oil, among others, has had a variety of claims for the past 50 years that the 'new specification is dangerous for your car'. Some go so far as to claim that GL-5 does not even require a copper corrosion test (proving its hazard) when in fact it has a more stringent copper corrosion test spec than other gear oils. The general rule is that it takes 70 years for such rumors to cease so we have maybe another 20 years to go.
To illustrate the gravity of the problem we had a club member just recently who was nearly convinced to put an entirely unsuitable oil in his hypoid differential for fear of this non-existent 'hazard' from GL-5. Had he done so, actual damage would not have been prevented but, instead, virtually guaranteed.
. I kind of thought the issue had been settled until I got my Wagon and started looking around for info on it. I have been using GL1 in my 2A, with the overdrive, for decades with no problems - Have Fun.