Another take on the Oil debate
This is pretty solid information from my uncle. Hes an engineer and one of the smartest people i know. I boldfaced a section that seems rather important ot the PSD.
This is an Email conversation between dad and my uncle...
I thought I would send some information on motor oils. If you read any of the forum questions and answers you can get all kinds of misinformation.
I did a little bit of review and finally got my brain into gear concerning TBN. There are many different kinds of acids and bases. Examples of some common acids are sulfuric (battery) acid, acetic acid (vinegar), and lemon juice. Some common bases are some drain cleaners (lye, which may include potassium hydroxide (KOH) and sodium hydroxide (NaOH). Other bases include antacids (for stomach acid) and baking soda which contains sodium bicarbonate (NaHCO3).
After I have refined them a little bit, I will send some notes I got from the internet which may be worthwhile. In the mean time, TBN is Total Base Number and is expressed as the equivalent (in neutralizing power) milligrams of potassium hydroxide (KOH) per gram of oil. In practice the oil formulators use bases that may contain magnesium, calcium, etc.
The sulfur in diesel fuel tends to contaminate the crankcase oil from piston ring blow-by as sulfur dioxide. In the crankcase, moisture reacts with sulfur dioxide to create sulfuric acid. Oxidation of engine oil also contributes to formation of some weak acids. The acids that are formed then tend to corrode engine parts. The function of base additives (expressed as TBN) is to neutralize engine oil acids. As the base additives neutralize acids, they are used up (as is baking soda when it is used to clean corroded battery terminals). You can see that with low and ultra-low sulfur diesel fuels, the TBN for new oil can be lower than it was for the previous high sulfur diesel fuels because the potential for acid formation is reduced.
Of possible interest is a note I came across in a study of biodiesel fuel that indicated certain types produced much more acid during combustion, and that ended up causing faster depletion of the base additives. I don’t know that that has anything to do with the reprocessed greases/oils that you are using, but it might be good to have your oil tested at some point if you haven’t already done that. The following highlighted note was part of a discussion of TBN and TAN (Total Acid Number) that I came across.
In the past, standard practices for determining optimal drain intervals using fluid analysis have required testing the oil for TBN and TAN. The theory was that when new, an oil’s TBN is high and its TAN is low, and the longer the oil is used, TBN decreases while TAN increases. The point at which they meet is the optimal time to change the oil. It is important to note that ASTM D-4739 should be used when testing the TBN of used (in-service) oils as opposed to ASTM D-2896, which may be used when testing TBN in new oils. ASTM D-4739 uses a weaker acid for titration than does ASTM D-2896 and, therefore, produces slightly lower TBN results.
Historical test data shows the relationship between TBN and TAN to be quite consistent. TAN just begins to increase when TBN depletion reaches 50 percent. As the TBN drops below 50 percent, TAN begins increasing rapidly. So in reality, TBN depletion can reach about 65 percent before it becomes necessary to change the oil.
I am attaching an oil viscosity plot of several 5W-40 and 15W-40 oils on a partial ASTM grid. It looks somewhat like a log-log grid, but it was actually created by hand I believe in the mid-1940’s so that oil viscosity measurements would plot as straight lines. You will notice that on the 40 weight end of the plot they all cluster around 15 centistokes at 212F. However, at 0F the viscosity of 15W-40 is more than twice the viscosity of 5W-40 synthetic. The 5W-40 flows more easily on cold starts, and also reduces starter load. An additional benefit might accrue for use in the 6.0 liter Ford, which uses engine oil to operate the fuel injectors. Synthetic oils are tougher molecules and resist mechanical shearing which definitely can occur when oil is compressed and released as in this application. I mentioned to the service manager at Jim Townsend Ford in Shawnee that this arrangement sounded like an argument to use synthetic oil, and what did I find on line but a 5W-40 Motorcraft synthetic oil! It plots directly on top of the Shell Rotella T synthetic 5W-40. The Motul oil is what I use in my VW.
Interesting. Looks like Rotella 5W-40 synthetic is much better than motorcraft synthetic of same viscosity. I may have to start using a synthetic. I periodically send a sample of my oil to Blackstone for testing. On my last report, SUS viscosity was just a tad low at 210 degrees F(67.2 versus 69-80)., cSt viscosity @ 100deg. C. slightly low at 12.20(12.7-15.8)). Flashpoint was 410 versue averages of greater than 410. Lead was high at 9, when it should have around 5, but everything else was within normal ranges. I'll probably have it tested again at next oil change. What do you yhink about amsoil? That seems to be highly touted.
Actually if you look at lines 2 & 4, the Motorcraft and Rotella just about overlay each other. It might be that the Motorcraft is Rotella. Saybolt Universal Seconds is rarely used for motor oils. Centistokes is more universal for several reasons, and it is easier and probably more accurate to measure centistokes (actually centipoise and convert to centistokes) with a rotating spindle viscometer. Yes, 12.2 cSt is a little bit low. What oil is that? I would like to use synthetic, and probably will next time, but boy it is sure hard to come to grips with cost. I have a gallon of Rotella 5W-40. I just need to buy 3 more gallons.
Somewhere I have a curve to convert SUS to cSt, and if I come across it I will send it along. It is very nonlinear on the low end, so it takes a curve to do it easily. If you cut through all of the sales promotion hyperbole about Amsoil, I imagine it is a good oil. I am attaching a plot of their 5W-40 diesel oil specs. They tout being a PAO (polyalphaolefin) basestock oil, and that is good. PAO basestocks are synthesized from smaller homogeneous molecules, and the larger the synthesized molecule the higher the viscosity of the basestock. (At Centrilift we used PAO oils from 6 cSt to 100 cSt at 100C for electric motor fills. I was instrumental in getting the conversion from white oils to PAO oils because they are tougher and stand the heat better.) I think some synthetic motor oils have some diesters in them, and that also is good, but that is just my speculation. Between the three oils, I would let price dictate, because I think they are pretty similar. I wouldn’t consider Castrol because from all I know it is made from a highly refined hydrogenated white oil, but it is still a mineral oil.
Last edited by Clay Henry; 10-08-2009 at 07:39 PM.