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Jul 16, 2002
Alamogordo, NM
I heard it first from George Morrison who said, "TBN has no relevance for gasoline powered engines. TBN is for diesel engines, diesel oil, to neutralize acids by products produced from the diesel fuel. A gasoline engine does not produce acid by-products in that manner, thus TBN is not a gasoline oil determinate." Then I heard it again from WearCheck, who did my last oil analysis and gave me TAN rather than TBN on my last report, "We give TAN for gasoline engines because it's a much better test than TBN. It's a direct physical measurement of the buildup of acid in the oil." I did a google search and found a paper devoted to this exact subject by Swepco USA.
Because the chemistries used to make up TBN can differ in quality and ability to maintain effectiveness over extended drain intervals, the TAN test and results is the most accurate measure of the oils on-going ability to resist degradation from greater level of acidity. This definitely makes the TAN test the preferred test method for used oil analysis...expecially in determining extended drain capabilities of a wide variety of oils.
Finally, I emailed Dexsil and asked, "Which method, TAN or TBN, is best for determining the useful life of motor oil in a gasoline engine?" Their answer:
The TAN is the kit you would want to use for a gasoline engine. (The TBN kit is used for diesel powered engines.) The TAN kit determines the amount of acid build-up due to oxidation of the oil. However, there are other considerations in determining the useful life of motor oils - i.e. water, particulate matter (due to friction of the metal parts)...
If TAN is the better test for gasoline powered engines, why do so many folks use TBN?
Jay, General rule of thumb is: TBN - TAN should be greater than 0.0 This means you still have some reserve alkalinity ...if you use a lower limit of 2.0 for gas engines or 4.0 for diesels - using ASTM D-4739, you'll be fine. The reason for the more conservative lower limit on diesels is due to the extreme damage soot and acids can cause, along with the 15k-25k drain intervals in OTR trucks or 250-300 hr drain intervals in off road equipment and marine diesels. As TBN decreases, your ability to suspend and disperse soot also is affected .... Ted
I look at it like this. Total Acid Number is great for potentially sensitive acid environments such as gear lubes and diesel oils, because there is usually an accepted limit or threshold for replacement of the oil when it reaches a certain acid value. Total Base Number is best for gasoline powered engines since it tells you how much reserve alkalinity is left to fight acids. A tbn below 2 usually indicates severe base chemistry depletion. If the analysis company only wants to give TAN, then have them tell you what the acid threshold for replacement of the oil is.
WearCheck told me a TAN of 3.5 was their recommended cut-off for motor oil. The Swepco link above says that a TAN of 5 is often used as a condemnation limit. I can have WearCheck do either test for my gasoline engine UOA reports, but I'm hearing more and more that TAN is the better of the two tests for gasoline engines.
Here is question to ask WearCheck or whomever: Which is more sensitive to changes in acid content, tbn or TAN? I say tbn.
Hi, this subject has been covered in a thread here previously and in some depth under - "TAN or TBN" Both are relevant to an end user and the last thread on the subject pointed out examples of why and how ExxonMobil's Lab in Australia reports on both and has done so for the last several years Regards
Thanks for pointing me to the thread TAN or TBN, Doug. It was a good thread. I had done a search and could not find anything on the topic. I think I will try TAN because I've been very unhappy with the TBN values I've been getting from various labs. Maybe TAN will be more consistent and reliable than TBN was for me. WearCheck, NC definitely prefers TAN for gasoline engines.
Jay, I'm no chemist, but if your TBN is fluctuating in an otherwise "unchanged" engine, then It won't matter which reading you go with. Something's happening in your engine or the environment is/has changed (humidity, temp, etc.) I would personally go with the TBN reading as it tells you how much detergent is left, rather than how much acid is in it. Rick EDIT: BTW, stick with one lab. You will most likely get different readings from different labs.....whether you want TAN or TBN. [ February 16, 2004, 09:36 PM: Message edited by: Last_Z ]
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