{"id":4690,"date":"2026-06-10T10:45:54","date_gmt":"2026-06-10T15:45:54","guid":{"rendered":"https:\/\/www.bioblend.com\/?p=4690"},"modified":"2026-06-10T10:45:54","modified_gmt":"2026-06-10T15:45:54","slug":"tan-limits-for-mineral-oil-vs-natural-esters","status":"publish","type":"post","link":"https:\/\/www.bioblend.com\/fr\/tan-limits-for-mineral-oil-vs-natural-esters\/","title":{"rendered":"Total Acid Number (TAN) Limits for Mineral Oil vs. Natural Esters"},"content":{"rendered":"<p><span style=\"font-weight: 400;\">Total Acid Number (TAN) is often treated as a simple or automatic \u201cchange the oil\u201d trigger\u2014but that shortcut can lead to bad decisions when you compare mineral hydraulic oils to natural\/ester-based fluids. Mineral oils typically start with very low TAN and are commonly condemned near ~2.0 mg KOH\/g, while esters begin higher and can operate safely at two-to-four times that level when corrosion protection and <a href=\"https:\/\/www.bioblend.com\/increased-viscosity-index-with-bioblends-esyn-lubricants\/\">viscosity<\/a> remain in control.<\/span><\/p>\n<p><span style=\"font-weight: 400;\">This overview explains why absolute TAN isn\u2019t the headline metric: what matters is the <\/span><i><span style=\"font-weight: 400;\">rise from new oil<\/span><\/i><span style=\"font-weight: 400;\">, the <\/span><i><span style=\"font-weight: 400;\">type\/strength of acids<\/span><\/i><span style=\"font-weight: 400;\"> being generated, and whether the additive system is still protecting metal surfaces. It also outlines practical monitoring ranges and decision checks\u2014especially rust\/copper corrosion performance, deposit formation, viscosity drift, and water control\u2014so you can interpret high TAN correctly in ester fluids instead of applying mineral-oil limits by default.<\/span><\/p>\n<p><b>The Basics:<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Mineral hydraulic oils<\/b><span style=\"font-weight: 400;\"> start with a very low TAN and are usually <\/span><b>condemned around 2.0 mg KOH\/g<\/b><span style=\"font-weight: 400;\">.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><a href=\"https:\/\/www.bioblend.com\/product-category\/hydraulic-oil\/\"><b>Natural\/ester-based hydraulic oils<\/b><\/a><span style=\"font-weight: 400;\"> start with a <\/span><b>higher TAN<\/b><span style=\"font-weight: 400;\"> and can typically <\/span><b>run safely at TAN values two-to-four times higher<\/b><span style=\"font-weight: 400;\"> than mineral oils, provided corrosion tests are still passing and viscosity hasn\u2019t run away.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">The key isn\u2019t the absolute TAN; it\u2019s <\/span><b>how much it has risen vs. new oil, what kind of acids they are, and whether the additive package is still protecting metal.<\/b><\/p>\n<h2><b>1. How TAN Compares: Mineral vs Natural\/Ester Hydraulic Oils<\/b><\/h2>\n<div class='et-box et-shadow'>\n\t\t\t\t\t<div class='et-box-content'>Summary: Mineral hydraulic oils often start around 0.05\u20130.3 mg KOH\/g, while natural or ester-based fluids often start higher, around 0.3\u20132.0 mg KOH\/g depending on the formula. A TAN of 1.2 could be a warning sign in mineral oil, but it might be normal for a fresh ester fluid.<\/div><\/div>\n<p><b>TAN (Total Acid Number)<\/b><span style=\"font-weight: 400;\"> is mg of KOH needed to neutralize acids in 1 g of oil, typically measured by ASTM D664.\u00a0<\/span><\/p>\n<p><b>Typical <\/b><b><i>new-oil<\/i><\/b><b> TAN<\/b><\/p>\n<p><b>Petroleum-based hydraulic oils (HLP \/ \u201cregular\u201d mineral oil):<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">New-oil TAN is usually <\/span><b>~0.05\u20130.3 mg KOH\/g<\/b><span style=\"font-weight: 400;\">.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">A Quaker Houghton skill-builder gives a representative value of <\/span><b>0.2 mg KOH\/g<\/b><span style=\"font-weight: 400;\"> for a mineral hydraulic fluid.\u00a0<\/span><\/li>\n<\/ul>\n<p><b>Natural \/ ester-based hydraulic fluids<\/b><span style=\"font-weight: 400;\"> (I\u2019ll lump together natural triglyceride HETG and ester-based HFDU\/HEES-type fluids, since they behave similarly from a TAN standpoint):<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">The base oil has <\/span><b>residual fatty acids<\/b><span style=\"font-weight: 400;\"> plus sometimes mildly acidic additives, so the starting TAN is <\/span><b>higher<\/b><span style=\"font-weight: 400;\">, often <\/span><b>0.3\u20132.0 mg KOH\/g<\/b><span style=\"font-weight: 400;\"> depending on formulation.\u00a0<\/span><\/li>\n<li><span style=\"font-weight: 400;\">The Quaker Houghton data sheet shows ester-based hydraulic fluids with initial TANs of <\/span><b>0.4, 1.1 and 2.0 mg KOH\/g<\/b><span style=\"font-weight: 400;\">, all higher than the 0.2 mg KOH\/g mineral reference.<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">So if you compare a used mineral oil at TAN 1.2 to a fresh natural ester at TAN 1.2, <\/span><b>the absolute numbers are the same, but the meaning is not<\/b><span style=\"font-weight: 400;\">. For the mineral oil, that\u2019s a big increase from ~0.1. For the ester, that might just be its \u201cborn that way\u201d TAN.<\/span><\/p>\n<h2><b>2. How TAN Relates to Corrosion Protection<\/b><\/h2>\n<div class='et-box et-shadow'>\n\t\t\t\t\t<div class='et-box-content'>Summary: TAN does not directly measure corrosion risk. Different oils create different kinds of acids. Mineral oil oxidation can create stronger acids and sludge, while ester fluids may contain weaker acids that count toward TAN but are less aggressive to metal.<\/div><\/div>\n<p><span style=\"font-weight: 400;\">Important nuance: <\/span><b>TAN is an indirect indicator<\/b><span style=\"font-weight: 400;\"> of oxidation\/ageing and potential corrosiveness, but it <\/span><b>does not directly measure corrosion risk<\/b><span style=\"font-weight: 400;\">. Several reasons:<\/span><\/p>\n<ol>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Strength and type of acids<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Mineral oil oxidation tends to generate <\/span><b>short-chain, stronger organic acids<\/b><span style=\"font-weight: 400;\"> (and associated sludge\/varnish) that can attack steel and yellow metals; TAN rises as these accumulate.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Natural and synthetic esters often have <\/span><b>weak residual fatty acids<\/b><span style=\"font-weight: 400;\"> built in from day one. These count toward TAN but are <\/span><b>far less aggressive<\/b><span style=\"font-weight: 400;\"> toward metal.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Polarity and solubility of by-products<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Ester-based fluids are <\/span><b>more polar<\/b><span style=\"font-weight: 400;\">, so oxidation products, soot and varnish <\/span><b>dissolve better<\/b><span style=\"font-weight: 400;\"> in the fluid rather than dropping out onto surfaces. That allows them to tolerate higher TAN values before you see deposits and sticking valves.\u00a0<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Mineral oils are less polar; similar oxidation by-products tend to <\/span><b>drop out earlier<\/b><span style=\"font-weight: 400;\"> as sludge\/varnish, causing sticky valves and fouling even at comparatively lower TAN.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Additive system (inhibitors)<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Rust and yellow-metal protection comes from inhibitors (e.g., amine phosphate, sulfonate, etc.), not from having a TAN of \u201c0.10 vs 0.30\u201d.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Your <\/span><b>BioLube LV<\/b><span style=\"font-weight: 400;\"> notes show a dedicated corrosion inhibitor (K-CORR 200-L) at a very low treat rate and nitrogen blanketing of the finished product, clear evidence that corrosion control is being engineered chemically, not by chasing ultra-low TAN.\u00a0<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<p><span style=\"font-weight: 400;\">So, <\/span><b>for corrosion<\/b><span style=\"font-weight: 400;\">:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Rising TAN <\/span><b>in a mineral oil<\/b><span style=\"font-weight: 400;\"> is a pretty direct red flag for more aggressive acids \u2192 more corrosion risk.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Rising TAN <\/span><b>in an ester<\/b><span style=\"font-weight: 400;\"> needs to be interpreted more carefully:<\/span>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Some of the TAN is weak, built-in acidity.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">You must cross-check with <\/span><b>ASTM D665 (rust), D130 (copper strip)<\/b><span style=\"font-weight: 400;\"> and visual inspection for sludge\/varnish to see if the acids that are forming are actually corrosive.<\/span><\/p>\n<h2><b>Condemning Limits: How High Can TAN Go?<\/b><\/h2>\n<p><span style=\"font-weight: 400;\">These are <\/span><b>typical industry practices<\/b><span style=\"font-weight: 400;\">, not hard standards. OEMs, the specific fluid supplier, and your oil lab will always have the final say.<\/span><\/p>\n<h3><b>3.1 Petroleum Several Industry Sources:<\/b><\/h3>\n<div class='et-box et-shadow'>\n\t\t\t\t\t<div class='et-box-content'>Summary: For mineral oil, rising TAN is usually a more direct warning that the oil is degrading and could start causing corrosion or deposits.<\/div><\/div>\n<ul>\n<li><b>Quaker Houghton<\/b><span style=\"font-weight: 400;\"> explicitly recommends refreshing <\/span><b>mineral-oil-based hydraulic fluids at TAN \u2248 2.0 mg KOH\/g<\/b><span style=\"font-weight: 400;\">, with a fresh value ~0.2.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">A common \u201crule of thumb\u201d (TestOil) is to <\/span><b>condemn non-engine oils when TAN has doubled versus new oil<\/b><span style=\"font-weight: 400;\"> (for many mineral hydraulic oils that ends up around 1\u20132 mg KOH\/g).\u00a0<\/span><\/li>\n<li><span style=\"font-weight: 400;\">Fluid power articles often flag hydraulic oils as \u201cof concern\u201d once TAN gets <\/span><b>\u22651.0 mg KOH\/g<\/b><span style=\"font-weight: 400;\">, depending on the fluid type and system criticality.<\/span><\/li>\n<\/ul>\n<p><b>Practical envelope for typical mineral hydraulic oil:<\/b><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">New oil: <\/span><b>~0.05\u20130.3 mg KOH\/g<\/b><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Watch \/ increased monitoring:<\/b><span style=\"font-weight: 400;\"> TAN <\/span><span style=\"font-weight: 400;\">\u2273<\/span> <b>1.0\u20131.5 mg KOH\/g<\/b><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Typical condemn \/ change-out:<\/b><span style=\"font-weight: 400;\"> around <\/span><b>2.0 mg KOH\/g<\/b><span style=\"font-weight: 400;\">, or <\/span><b>+1.0\u20132.0 mg<\/b><span style=\"font-weight: 400;\"> above the new-oil TAN<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">Beyond ~2, the combination of more corrosive acids, additive depletion and sludge\/varnish risk makes keeping the oil in service risky for most hydraulic systems.<\/span><\/p>\n<h3><b>3.2 Natural Esters and Ester-Based Hydraulic Fluids<\/b><\/h3>\n<div class='et-box et-shadow'>\n\t\t\t\t\t<div class='et-box-content'>Summary: Natural ester and ester-based hydraulic fluids start with higher TAN values because of their chemistry. Some ester fluids can safely operate at higher TAN values when corrosion, viscosity, cleanliness, and water control remain acceptable. However, you still need to look for sudden increases in these various factors.<\/div><\/div>\n<p><span style=\"font-weight: 400;\">Here we have two overlapping realities:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Biodegradable \/ eco hydraulic fluids<\/b><span style=\"font-weight: 400;\"> (HETG\/HEES\/HFDU) used in hydraulics.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Natural esters used as transformer dielectrics<\/b><span style=\"font-weight: 400;\">, which have <\/span><i><span style=\"font-weight: 400;\">much stricter<\/span><\/i><span style=\"font-weight: 400;\"> TAN limits due to electrical insulation requirements (often TAN limit ~0.1\u20130.2 mg KOH\/g; that\u2019s a different world, so I\u2019ll keep the focus on hydraulics).\u00a0<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">For <\/span><b>ester-based hydraulic fluids<\/b><span style=\"font-weight: 400;\">, Quaker Houghton provides a nice comparative table:<\/span><\/p>\n<div class=\"table-wrapper\">\n<table class=\"tan-comparison-table\">\n<caption>Recommended Total Acid Number (TAN) limits for mineral hydraulic oil compared with ester-based HFD-U fluids.<\/caption>\n<thead>\n<tr>\n<th scope=\"col\">Fluid type<\/th>\n<th scope=\"col\">Initial TAN (mg KOH\/g)<\/th>\n<th scope=\"col\">Recommended max TAN (mg KOH\/g)<\/th>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td>Mineral hydraulic oil<\/td>\n<td>0.2<\/td>\n<td>2.0<\/td>\n<\/tr>\n<tr>\n<td>Ester-based HFD-U, competitor #1<\/td>\n<td>0.4<\/td>\n<td>4.0<\/td>\n<\/tr>\n<tr>\n<td>Ester-based HFD-U, competitor #2<\/td>\n<td>1.1<\/td>\n<td>5.0<\/td>\n<\/tr>\n<tr>\n<td>Ester-based HFD-U (QUINTOLUBRIC)<\/td>\n<td>2.0<\/td>\n<td>8.0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<p><span style=\"font-weight: 400;\">Key takeaways:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Ester fluids <\/span><b>start higher<\/b><span style=\"font-weight: 400;\"> and <\/span><b>run safely to higher TAN<\/b><span style=\"font-weight: 400;\"> than mineral oils.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">In Quaker\u2019s pump tests, their ester fluid showed <\/span><b>no visible wear, soot or varnish even at TAN \u2248 8<\/b><span style=\"font-weight: 400;\">, thanks to the base oil polarity and additive package.\u00a0<\/span><\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">For <\/span><b>natural triglyceride hydraulic fluids (HETG)<\/b><span style=\"font-weight: 400;\">:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">They behave like esters in terms of higher starting TAN and ability to \u201ctolerate\u201d higher TAN, but<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">Their <\/span><b>oxidation stability is poorer<\/b><span style=\"font-weight: 400;\"> than saturated synthetic esters, so in practice most suppliers are more conservative.\u00a0<\/span><\/li>\n<\/ul>\n<p><b>Practical envelope for natural\/ester hydraulic fluids:<\/b><\/p>\n<p><span style=\"font-weight: 400;\">These are broad, but reasonable working numbers if the OEM or supplier hasn\u2019t given explicit limits:<\/span><\/p>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><span style=\"font-weight: 400;\">New oil TAN: typically <\/span><b>0.3\u20132.0 mg KOH\/g<\/b><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Watch \/ increased monitoring:<\/b>\n<ul>\n<li><span style=\"font-weight: 400;\">Once TAN has climbed by <\/span><b>~1.0\u20132.0 mg KOH\/g above new-oil<\/b><span style=\"font-weight: 400;\">,<\/span><\/li>\n<li><span style=\"font-weight: 400;\">or absolute TAN is <\/span><b>in the 3\u20134 mg KOH\/g range<\/b><span style=\"font-weight: 400;\">.<\/span><\/li>\n<\/ul>\n<\/li>\n<li><b>Typical condemn \/ strong recommendation to change or recondition:<\/b>\n<ul>\n<li><span style=\"font-weight: 400;\">For many <\/span><b>natural triglyceride (HETG) hydraulics<\/b><span style=\"font-weight: 400;\">: <\/span><b>~4\u20135 mg KOH\/g<\/b><span style=\"font-weight: 400;\"> is a sensible \u201cdon\u2019t cross\u201d line, especially at higher operating temps.<\/span><\/li>\n<li><span style=\"font-weight: 400;\">For <\/span><b>high-performance synthetic esters (HEES\/HFDU)<\/b><span style=\"font-weight: 400;\">, some suppliers allow <\/span><b>up to 6\u20138 mg KOH\/g<\/b><span style=\"font-weight: 400;\"> (as in the QUINTOLUBRIC example), <\/span><i><span style=\"font-weight: 400;\">provided<\/span><\/i><span style=\"font-weight: 400;\"> corrosion, viscosity and cleanliness are still in spec.\u00a0<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><span style=\"font-weight: 400;\">In all cases, <\/span><b>trend is king<\/b><span style=\"font-weight: 400;\">: a sudden jump from TAN 1 \u2192 3 is more alarming than a slow drift from 2 \u2192 3 over several years.<\/span><\/p>\n<h2><b>4. How to Connect This Back to Corrosion Decisions<\/b><\/h2>\n<div class='et-box et-shadow'>\n\t\t\t\t\t<div class='et-box-content'>Summary: TAN should start the conversation, not end it. Before changing the oil, check whether the fluid is still protecting metal, staying clean, controlling water, and maintaining proper viscosity.<\/div><\/div>\n<p><span style=\"font-weight: 400;\">When you\u2019re deciding \u201cis this oil still safe, or is TAN condemning?\u201d, look at:<\/span><\/p>\n<ol>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>\u0394TAN vs. new oil<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Mineral: think \u201cnew + about 1\u20132 mg KOH\/g\u201d as your action band.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Natural\/esters: \u201cnew + about 2\u20133 mg KOH\/g\u201d is often acceptable, with a hard stop in the <\/span><b>4\u20135+<\/b><span style=\"font-weight: 400;\"> range unless the supplier says otherwise.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Corrosion and deposit tests<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Rust test (ASTM D665), copper strip (D130), filterability and visual inspection for sludge\/varnish.<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">If TAN is high but you still pass rust\/copper tests and the system is clean, the acids are likely weak and mostly solvated.<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Viscosity and water<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">Particularly for natural esters, <\/span><b>water plus heat = hydrolysis<\/b><span style=\"font-weight: 400;\">, which can spike TAN and generate more corrosive species; tight water control is crucial.\u00a0<\/span><\/li>\n<\/ul>\n<\/li>\n<li style=\"font-weight: 400;\" aria-level=\"1\"><b>Your specific formulation<\/b>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"2\"><span style=\"font-weight: 400;\">In your BioLube case, you\u2019ve got:<\/span>\n<ul>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><span style=\"font-weight: 400;\">A dedicated <\/span><b>corrosion inhibitor (K-CORR 200-L)<\/b><span style=\"font-weight: 400;\"> at extremely low treat rate, and<\/span><\/li>\n<li style=\"font-weight: 400;\" aria-level=\"3\"><b>Nitrogen treatment<\/b><span style=\"font-weight: 400;\"> of the finished product to slow oxidative TAN increase.\u00a0<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ol>\n<p><span style=\"font-weight: 400;\">That\u2019s exactly the pattern for an ester fluid intended to operate <\/span><b>safely at a higher TAN window than a mineral oil<\/b><span style=\"font-weight: 400;\">, while keeping corrosion fully controlled.<\/span><\/p>\n<p><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-4696 size-large\" src=\"https:\/\/www.bioblend.com\/wp-content\/uploads\/bioblend-hydraulic-oil-maintenance-steps-725x1024.png\" alt=\"The seven steps for maintaining hydraulic fluid along with applying TAN limits.\" width=\"725\" height=\"1024\" \/><\/p>\n<p><a href=\"https:\/\/www.bioblend.com\/contact-us\/\"><span style=\"font-weight: 400;\">Contact us<\/span><\/a><span style=\"font-weight: 400;\"> to learn more about the benefits of <\/span><a href=\"https:\/\/www.bioblend.com\/lubricants-total-cost-of-ownership\/\"><span style=\"font-weight: 400;\">using to biodegradable lubricants<\/span><\/a><span style=\"font-weight: 400;\">, or browse our full <\/span><a href=\"https:\/\/www.bioblend.com\/products\/\"><span style=\"font-weight: 400;\">product offerings<\/span><\/a><span style=\"font-weight: 400;\">. <\/span><\/p>\n<h2><b>Total Acid Number FAQs<\/b><\/h2>\n<h3><b>What is Total Acid Number in hydraulic oil?<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Total Acid Number, or TAN, measures the amount of potassium hydroxide required to neutralize acidic components in one gram of oil. It is commonly reported in mg KOH\/g and measured by ASTM D664.<\/span><\/p>\n<h3><b>What is a normal TAN for mineral hydraulic oil?<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">New mineral hydraulic oils commonly start around 0.05\u20130.3 mg KOH\/g. Many systems move into a watch range around 1.0\u20131.5 mg KOH\/g, depending on the fluid, system, and lab guidance.<\/span><\/p>\n<h3><b>What TAN level means hydraulic oil should be changed?<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">For many mineral hydraulic oils, TAN near 2.0 mg KOH\/g is commonly treated as a change-out point. You should also review viscosity, water, corrosion tests, filter condition, and OEM guidance before making the final decision.<\/span><\/p>\n<h3><b>Why do natural ester hydraulic fluids have higher TAN?<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Natural ester and ester-based hydraulic fluids often contain residual fatty acids, polar ester chemistry, and additive components that contribute to a higher starting TAN. That higher baseline does not automatically mean the oil is degraded.<\/span><\/p>\n<h3><b>Can ester hydraulic fluids operate safely at higher TAN?<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Yes. Many ester-based hydraulic fluids can operate safely at higher TAN values than mineral oil when corrosion protection, viscosity, cleanliness, and water content remain within acceptable limits.<\/span><\/p>\n<h3><b>Does a high TAN always mean corrosion is happening?<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">No. TAN indicates acidic components, but it does not directly measure corrosion. Use rust testing, copper strip corrosion, water content, viscosity, and system inspection to understand the actual risk.<\/span><\/p>\n<h3><b>Why is water control important in natural ester fluids?<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">Water and heat can accelerate hydrolysis in ester fluids. Hydrolysis can increase TAN and create more aggressive acidic species, so moisture control has a direct impact on fluid life.<\/span><\/p>\n<h3><b>Should I use the same TAN limit for mineral oil and natural ester hydraulic fluid?<\/b><\/h3>\n<p><span style=\"font-weight: 400;\">No. Mineral oils and ester-based hydraulic fluids start with different TAN values and age differently. Always compare used oil against the specific fluid\u2019s new-oil baseline and supplier guidance.<\/span><br \/>\n<script type=\"application\/ld+json\">\n{\n  \"@context\": \"https:\/\/schema.org\",\n  \"@type\": \"FAQPage\",\n  \"mainEntity\": [\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What is Total Acid Number in hydraulic oil?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Total Acid Number, or TAN, measures the amount of potassium hydroxide required to neutralize acidic components in one gram of oil. It is commonly reported in mg KOH\/g and measured by ASTM D664.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What is a normal TAN for mineral hydraulic oil?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"New mineral hydraulic oils commonly start around 0.05\u20130.3 mg KOH\/g. Many systems move into a watch range around 1.0\u20131.5 mg KOH\/g, depending on the fluid, system, and lab guidance.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"What TAN level means hydraulic oil should be changed?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"For many mineral hydraulic oils, TAN near 2.0 mg KOH\/g is commonly treated as a change-out point. You should also review viscosity, water, corrosion tests, filter condition, and OEM guidance before making the final decision.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Why do natural ester hydraulic fluids have higher TAN?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Natural ester and ester-based hydraulic fluids often contain residual fatty acids, polar ester chemistry, and additive components that contribute to a higher starting TAN. That higher baseline does not automatically mean the oil is degraded.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Can ester hydraulic fluids operate safely at higher TAN?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Yes. Many ester-based hydraulic fluids can operate safely at higher TAN values than mineral oil when corrosion protection, viscosity, cleanliness, and water content remain within acceptable limits.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Does a high TAN always mean corrosion is happening?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"No. TAN indicates acidic components, but it does not directly measure corrosion. Use rust testing, copper strip corrosion, water content, viscosity, and system inspection to understand the actual risk.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Why is water control important in natural ester fluids?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"Water and heat can accelerate hydrolysis in ester fluids. Hydrolysis can increase TAN and create more aggressive acidic species, so moisture control has a direct impact on fluid life.\"\n      }\n    },\n    {\n      \"@type\": \"Question\",\n      \"name\": \"Should I use the same TAN limit for mineral oil and natural ester hydraulic fluid?\",\n      \"acceptedAnswer\": {\n        \"@type\": \"Answer\",\n        \"text\": \"No. Mineral oils and ester-based hydraulic fluids start with different TAN values and age differently. Always compare used oil against the specific fluid\u2019s new-oil baseline and supplier guidance.\"\n      }\n    }\n  ]\n}\n<\/script><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Total Acid Number (TAN) is often treated as a simple or automatic \u201cchange the oil\u201d trigger\u2014but that shortcut can lead to bad decisions when you compare mineral hydraulic oils to natural\/ester-based fluids. Mineral oils typically start with very low TAN and are commonly condemned near ~2.0 mg KOH\/g, while esters begin higher and can operate [&hellip;]<\/p>\n","protected":false},"author":19,"featured_media":4699,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"off","_et_pb_old_content":"","_et_gb_content_width":"","inline_featured_image":false,"footnotes":""},"categories":[102,105],"tags":[106,98],"class_list":["post-4690","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-hydraulic-oil","category-renewable-lubricants","tag-biodegradable","tag-lubricants"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.8 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Total Acid Number TAN Limits: Mineral Oil vs Natural Esters<\/title>\n<meta name=\"description\" content=\"Learn how TAN differs in mineral hydraulic oils and natural ester fluids, 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