{"id":100178,"date":"2026-02-15T20:25:18","date_gmt":"2026-02-15T20:25:18","guid":{"rendered":"https:\/\/vibromera.eu\/?post_type=calculator&#038;p=100178"},"modified":"2026-04-05T15:37:51","modified_gmt":"2026-04-05T15:37:51","slug":"oil-viscosity-temperature","status":"publish","type":"calculator","link":"https:\/\/vibromera.eu\/bn\/calculators\/oil-viscosity-temperature\/","title":{"rendered":"Oil Viscosity\u2013Temperature Calculator | Walther ASTM D341"},"content":{"rendered":"\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"WebApplication\",\"name\":\"Oil Viscosity\u2013Temperature Calculator\",\"description\":\"Calculate kinematic viscosity at any temperature using Walther equation. VI per ASTM D2270. ISO VG classes.\",\"url\":\"https:\/\/vibromera.eu\/calculators\/oil-viscosity-temperature\/\",\"applicationCategory\":\"Engineering Calculator\",\"operatingSystem\":\"Any\",\"offers\":{\"@type\":\"Offer\",\"price\":\"0\",\"priceCurrency\":\"EUR\"},\"creator\":{\"@type\":\"Organization\",\"name\":\"Vibromera\",\"url\":\"https:\/\/vibromera.eu\/\"},\"datePublished\":\"2024-01-01\",\"dateModified\":\"2025-06-01\",\"inLanguage\":\"en\",\"isAccessibleForFree\":true}<\/script>\n\n<script type=\"application\/ld+json\">{\"@context\":\"https:\/\/schema.org\",\"@type\":\"FAQPage\",\"mainEntity\":[\n{\"@type\":\"Question\",\"name\":\"What is the Walther equation?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"The Walther (ASTM D341) equation: log log(\u03bd + 0.7) = A \u2212 B \u00d7 log(T), where T is in Kelvin. It produces a straight line on ASTM viscosity-temperature paper. Accurate for mineral oils from -20\u00b0C to 150\u00b0C.\"}},\n{\"@type\":\"Question\",\"name\":\"What is Viscosity Index (VI)?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"VI indicates how much viscosity changes with temperature. Higher VI = less change. Mineral oils: VI \u2248 80-100, synthetic PAO: VI \u2248 120-160, multigrade engine oils: VI > 150.\"}},\n{\"@type\":\"Question\",\"name\":\"What is ISO VG classification?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"ISO VG classifies industrial lubricants by kinematic viscosity at 40\u00b0C. VG 32 means \u03bd\u2084\u2080 \u2248 32 cSt. Range: VG 2 to VG 1500.\"}},\n{\"@type\":\"Question\",\"name\":\"How accurate is the Walther equation?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Very accurate for mineral oils (-20 to 150\u00b0C). Less accurate for synthetics, very low temps (near pour point), or very high temps (near flash point).\"}},\n{\"@type\":\"Question\",\"name\":\"What is the optimal operating viscosity range?\",\"acceptedAnswer\":{\"@type\":\"Answer\",\"text\":\"Most bearings and gears operate optimally at 13-100 cSt. Below 13 cSt: boundary lubrication risk. Above 100 cSt: excessive churning losses. Exact range depends on application speed and load.\"}}\n]}<\/script>\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.googleapis.com\">\n\n<link rel=\"preconnect\" href=\"https:\/\/fonts.gstatic.com\" crossorigin>\n\n<link href=\"https:\/\/fonts.googleapis.com\/css2?family=DM+Sans:ital,opsz,wght@0,9..40,300;0,9..40,400;0,9..40,500;0,9..40,600;0,9..40,700;1,9..40,400&#038;family=JetBrains+Mono:wght@400;500;600&#038;family=Fraunces:opsz,wght@9..144,700;9..144,800&#038;display=swap\" rel=\"stylesheet\">\n\n<link rel=\"stylesheet\" 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16px;font-size:13px;color:var(--vc-ink-muted)}.vc-footer a{color:var(--vc-accent);text-decoration:none}.vc-footer-links{margin-top:8px;font-size:12px}.vc-footer-links a{margin:0 8px}\n@media print{.vc-section-body{max-height:none!important}.vc-faq-a{max-height:none!important}.vc-results{max-height:none!important;padding:24px!important}.vc-copy-btn,.vc-section-chevron,.vc-faq-chevron,.vc-presets,.vc-promo{display:none!important}}\n.vc-viz{margin:20px 0;background:var(--vc-surface);border:1px solid var(--vc-border-light);border-radius:var(--vc-radius);padding:16px;overflow:hidden}.vc-viz svg{width:100%;height:auto;display:block}.vc-viz-title{font-family:var(--vc-mono);font-size:11px;font-weight:500;letter-spacing:0.1em;text-transform:uppercase;color:var(--vc-ink-muted);margin-bottom:12px}\n<\/style>\n\n<div class=\"vc-calculator\" id=\"vc-oil-visc\">\n<header class=\"vc-header\"><p class=\"vc-header-eyebrow\">Free Engineering Tool<\/p><h1 class=\"vc-header-title\">Oil Viscosity\u2013Temperature Calculator<\/h1><p class=\"vc-header-subtitle\">Calculate kinematic viscosity at any temperature using the Walther (ASTM D341) equation. Viscosity Index per ASTM D2270. Optimal operating range and pour point estimation.<\/p><div class=\"vc-badges\"><span class=\"vc-badge\">Walther \/ ASTM D341<\/span><span class=\"vc-badge\">Viscosity Index<\/span><span class=\"vc-badge\">ISO VG<\/span><span class=\"vc-badge\">Pour Point<\/span><\/div><\/header>\n\n<div class=\"vc-card\">\n    <form class=\"vc-form\" id=\"vc-form\" autocomplete=\"off\">\n        <div class=\"vc-form-grid\">\n            <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-v40\">\u03bd at 40\u00b0C <span class=\"vc-label-hint\">(cSt = mm\u00b2\/s)<\/span><\/label><input class=\"vc-input\" type=\"number\" id=\"vc-v40\" step=\"any\" value=\"68\" placeholder=\"e.g. 68\"><\/div>\n            <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-v100\">\u03bd at 100\u00b0C <span class=\"vc-label-hint\">(cSt)<\/span><\/label><input class=\"vc-input\" type=\"number\" id=\"vc-v100\" step=\"any\" value=\"8.7\" placeholder=\"e.g. 8.7\"><\/div>\n            <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-tgt\">Target Temperature <span class=\"vc-label-hint\">(\u00b0C)<\/span><\/label><input class=\"vc-input\" type=\"number\" id=\"vc-tgt\" step=\"any\" value=\"60\" placeholder=\"e.g. 60\"><\/div>\n            <div class=\"vc-field\"><label class=\"vc-label\" for=\"vc-vg\">ISO VG Class <span class=\"vc-label-hint\">(auto-fills \u03bd40\/\u03bd100)<\/span><\/label><select class=\"vc-select\" id=\"vc-vg\"><option value=\"\">\u2014 Custom \u2014<\/option><option value=\"10\">VG 10<\/option><option value=\"15\">VG 15<\/option><option value=\"22\">VG 22<\/option><option value=\"32\">VG 32<\/option><option value=\"46\">VG 46<\/option><option value=\"68\" selected>VG 68<\/option><option value=\"100\">VG 100<\/option><option value=\"150\">VG 150<\/option><option value=\"220\">VG 220<\/option><option value=\"320\">VG 320<\/option><option value=\"460\">VG 460<\/option><option value=\"680\">VG 680<\/option><option value=\"1000\">VG 1000<\/option><option value=\"1500\">VG 1500<\/option><\/select><\/div>\n        <\/div>\n        <div class=\"vc-presets\"><div class=\"vc-presets-label\">Quick presets<\/div>\n            <button type=\"button\" class=\"vc-preset-btn\" data-v40=\"32\" data-v100=\"5.4\" data-t=\"60\" data-vg=\"32\">VG 32 @ 60\u00b0C<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-v40=\"68\" data-v100=\"8.7\" data-t=\"80\" data-vg=\"68\">VG 68 @ 80\u00b0C<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-v40=\"220\" data-v100=\"19\" data-t=\"50\" data-vg=\"220\">VG 220 @ 50\u00b0C<\/button>\n            <button type=\"button\" class=\"vc-preset-btn\" data-v40=\"460\" data-v100=\"31\" data-t=\"70\" data-vg=\"460\">VG 460 @ 70\u00b0C<\/button>\n        <\/div>\n    <\/form>\n    <div class=\"vc-results\" id=\"vc-results\">\n        <div class=\"vc-results-head\"><h2 class=\"vc-results-title\">Viscosity Results<\/h2><button type=\"button\" class=\"vc-copy-btn\" id=\"vc-copy-btn\"><svg width=\"14\" height=\"14\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><rect x=\"9\" y=\"9\" width=\"13\" height=\"13\" rx=\"2\"\/><path d=\"M5 15H4a2 2 0 01-2-2V4a2 2 0 012-2h9a2 2 0 012 2v1\"\/><\/svg> Copy<\/button><\/div>\n        <div class=\"vc-result-grid\">\n            <div class=\"vc-rcard vc-rcard-primary\"><div class=\"vc-rcard-label\">Viscosity at Target Temperature<\/div><div class=\"vc-rcard-value\" id=\"vc-r-visc\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Viscosity Index (VI)<\/div><div class=\"vc-rcard-value\" id=\"vc-r-vi\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Operating Range Check<\/div><div class=\"vc-rcard-value\" id=\"vc-r-range\" style=\"font-size:14px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Walther Constant A<\/div><div class=\"vc-rcard-value\" id=\"vc-r-A\" style=\"font-size:18px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Walther Constant B<\/div><div class=\"vc-rcard-value\" id=\"vc-r-B\" style=\"font-size:18px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Reference: \u03bd40 \/ \u03bd100<\/div><div class=\"vc-rcard-value\" id=\"vc-r-ref\" style=\"font-size:16px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Estimated Pour Point<\/div><div class=\"vc-rcard-value\" id=\"vc-r-pour\" style=\"font-size:18px\">\u2014<\/div><\/div>\n            <div class=\"vc-rcard\"><div class=\"vc-rcard-label\">Dynamic Viscosity (\u03b7)<\/div><div class=\"vc-rcard-value\" id=\"vc-r-dyn\" style=\"font-size:18px\">\u2014<\/div><\/div>\n        <\/div>\n        <div class=\"vc-viz\" id=\"vc-viz\"><div class=\"vc-viz-title\">Walther Chart \u2014 Viscosity vs Temperature<\/div><div id=\"vc-viz-svg\"><\/div><\/div>\n    <\/div>\n<\/div>\n\n<div class=\"vc-section vc-open\" id=\"vc-sec-theory\">\n    <button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"true\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udcd8<\/span><span class=\"vc-section-title\">Theory, Formulas &amp; ISO VG Table<\/span><\/span><svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button>\n    <div class=\"vc-section-body\"><div class=\"vc-section-inner vc-theory\">\n        <h3>Walther Equation (ASTM D341)<\/h3>\n        <div class=\"vc-formula-box\" id=\"vc-katex-1\"><\/div>\n        <p>Where \u03bd is kinematic viscosity in mm\u00b2\/s (cSt), T is absolute temperature (K), and A, B are constants determined from two reference points.<\/p>\n        <h3>Viscosity Index (ASTM D2270)<\/h3>\n        <div class=\"vc-formula-box\" id=\"vc-katex-2\"><\/div>\n        <p>VI compares the oil&#8217;s viscosity-temperature behavior to two reference oils: L (VI=0, naphthenic) and H (VI=100, paraffinic). Higher VI = less viscosity change with temperature.<\/p>\n        <h3>Practical Example<\/h3>\n        <div class=\"vc-example-box\"><div class=\"vc-example-title\">Example \u2014 VG 68 at 80\u00b0C<\/div>\n            <p><strong>Given:<\/strong> \u03bd\u2084\u2080=68 cSt, \u03bd\u2081\u2080\u2080=8.7 cSt<\/p>\n            <p>Walther: A=8.8445, B=3.5912<\/p>\n            <p>At 80\u00b0C (353.15 K): log log(\u03bd+0.7)=8.8445\u22123.5912\u00d7log(353.15)=8.8445\u22129.1470=\u22120.3025<\/p>\n            <p>\u03bd = 10^(10^(\u22120.3025))\u22120.7 = <strong>17.6 cSt<\/strong><\/p>\n            <p>VI \u2248 98 (typical mineral oil)<\/p>\n        <\/div>\n        <h3>ISO VG Reference Table<\/h3>\n        <table class=\"vc-table\"><thead><tr><th>ISO VG<\/th><th>\u03bd at 40\u00b0C (cSt)<\/th><th>\u03bd at 100\u00b0C (cSt)<\/th><th>Typical Application<\/th><\/tr><\/thead><tbody>\n            <tr><td>VG 10<\/td><td>10<\/td><td>2.6<\/td><td>Spindle oils, hydraulics<\/td><\/tr>\n            <tr><td>VG 22<\/td><td>22<\/td><td>4.4<\/td><td>Hydraulic systems<\/td><\/tr>\n            <tr><td>VG 32<\/td><td>32<\/td><td>5.4<\/td><td>Hydraulic, light bearings<\/td><\/tr>\n            <tr><td>VG 46<\/td><td>46<\/td><td>6.8<\/td><td>Hydraulic, general bearings<\/td><\/tr>\n            <tr><td>VG 68<\/td><td>68<\/td><td>8.7<\/td><td>Heavy hydraulic, light gears<\/td><\/tr>\n            <tr><td>VG 100<\/td><td>100<\/td><td>11.4<\/td><td>Circulating, light gears<\/td><\/tr>\n            <tr><td>VG 150<\/td><td>150<\/td><td>15<\/td><td>Gears, bearings<\/td><\/tr>\n            <tr><td>VG 220<\/td><td>220<\/td><td>19<\/td><td>Industrial gears<\/td><\/tr>\n            <tr><td>VG 320<\/td><td>320<\/td><td>24.5<\/td><td>Heavy gears, worm<\/td><\/tr>\n            <tr><td>VG 460<\/td><td>460<\/td><td>31<\/td><td>Heavily loaded gears<\/td><\/tr>\n            <tr><td>VG 680<\/td><td>680<\/td><td>40<\/td><td>Very heavy gears<\/td><\/tr>\n            <tr><td>VG 1000<\/td><td>1000<\/td><td>52<\/td><td>Open gears<\/td><\/tr>\n            <tr><td>VG 1500<\/td><td>1500<\/td><td>68<\/td><td>Open gears, wire ropes<\/td><\/tr>\n        <\/tbody><\/table>\n        <div class=\"vc-info-box\"><p><strong>\ud83d\udca1 Optimal range:<\/strong> Most bearings and gears operate best at 13\u2013100 cSt. Below 13 cSt boundary lubrication risk; above 100 cSt excessive churning.<\/p><\/div>\n    <\/div><\/div>\n<\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-related\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\ud83d\udd17<\/span><span class=\"vc-section-title\">Related Calculators<\/span><\/span><svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-related\"><a class=\"vc-related-link\" href=\"\/calculators\/gear-oil-quantity\/\">Gear Oil Quantity<\/a><a class=\"vc-related-link\" href=\"\/calculators\/oil-change-interval\/\">Oil Change Interval<\/a><a class=\"vc-related-link\" href=\"\/calculators\/density-mass-volume\/\">Density Calculator<\/a><\/div><\/div><\/div><\/div>\n\n<div class=\"vc-section\" id=\"vc-sec-faq\"><button type=\"button\" class=\"vc-section-toggle\" aria-expanded=\"false\"><span class=\"vc-section-toggle-text\"><span class=\"vc-section-icon\">\u2753<\/span><span class=\"vc-section-title\">Frequently Asked Questions<\/span><\/span><svg class=\"vc-section-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button><div class=\"vc-section-body\"><div class=\"vc-section-inner\"><div class=\"vc-faq-list\" id=\"vc-faq-list\"><\/div><\/div><\/div><\/div>\n\n<div class=\"vc-promo\"><div class=\"vc-promo-text\"><strong>Vibromera<\/strong> \u2014 Portable 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W2=Math.log10(Math.log10(v100+0.7));\n        var logT1=Math.log10(T1),logT2=Math.log10(T2);\n        var B=(W1-W2)\/(logT2-logT1);var A=W1+B*logT1;\n        var W3=A-B*Math.log10(T3);var v=Math.pow(10,Math.pow(10,W3))-0.7;\n        return{v:v,A:A,B:B};\n    }\n\n    function approxVI(v40,v100){\n        if(v40<2||v100<0.5)return NaN;\n        \/\/ Simplified ASTM D2270 approximation\n        var L,H;\n        if(v100>=2&&v100<3.8){L=1.14*v100*v100+3.01*v100+22.1;H=0.838*v100*v100-0.22*v100+14.3;}\n        else if(v100<70){L=0.8353*v100*v100+14.67*v100-216;H=0.168*v100*v100+11.85*v100-97;\n            if(v100<6.5){L=7.994*v100+38;H=4.1*v100+15.5}}\n        else{L=0.8353*v100*v100+14.67*v100-216;H=0.168*v100*v100+11*v100-97}\n        if(isNaN(L)||isNaN(H)||L<=H)return NaN;\n        return Math.round(((L-v40)\/(L-H))*100);\n    }\n\n    function estimatePourPoint(v40,vi){\n        \/\/ Very rough: pour point correlates with viscosity and VI\n        var base=-15-vi*0.05;\n        if(v40>200) base+=5;\n        if(v40>500) base+=5;\n        return Math.round(base\/3)*3; \/\/ round to nearest 3\n    }\n\n    function drawWaltherChart(v40,v100,tgt,vt,cA,cB){\n        var el=$('vc-viz-svg');if(!el)return;\n        var W=600,H=350,ml=65,mr=25,mt=25,mb=45,pw=W-ml-mr,ph=H-mt-mb;\n        var tMin=0,tMax=120,vMin=2,vMax=1000;\n        var ltMin=Math.log10(tMin+273.15),ltMax=Math.log10(tMax+273.15);\n        var wMin=Math.log10(Math.log10(vMin+.7)),wMax=Math.log10(Math.log10(vMax+.7));\n        function xP(t){return ml+(Math.log10(t+273.15)-ltMin)\/(ltMax-ltMin)*pw}\n        function yP(v){var w=Math.log10(Math.log10(Math.max(v,.8)+.7));return mt+ph-(w-wMin)\/(wMax-wMin)*ph}\n        function viscAt(t){var w=cA-cB*Math.log10(t+273.15);var r=Math.pow(10,Math.pow(10,w))-.7;return r>0?r:.5}\n        var o='<svg viewBox=\"0 0 600 350\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\">';\n        o+='<rect x=\"'+xP(40)+'\" y=\"'+mt+'\" width=\"'+(xP(60)-xP(40))+'\" height=\"'+ph+'\" fill=\"var(--vc-green)\" opacity=\"0.06\"\/>';\n        o+='<text x=\"'+((xP(40)+xP(60))\/2)+'\" y=\"'+(mt+13)+'\" text-anchor=\"middle\" font-family=\"var(--vc-mono)\" font-size=\"8\" fill=\"var(--vc-green)\" opacity=\"0.7\">Optimal 40\\u201360\\u00b0C<\/text>';\n        var vHi=v40*1.1,vLo=v40*.9,byH=yP(vHi),byL=yP(vLo);\n        if(byL>mt&&byH<mt+ph){o+='<rect x=\"'+ml+'\" y=\"'+byH+'\" width=\"'+pw+'\" height=\"'+(byL-byH)+'\" fill=\"var(--vc-blue)\" opacity=\"0.06\"\/>';\n            o+='<text x=\"'+(ml+pw-2)+'\" y=\"'+(byH+10)+'\" text-anchor=\"end\" font-family=\"var(--vc-mono)\" font-size=\"8\" fill=\"var(--vc-blue)\" opacity=\"0.6\">ISO VG \\u00b110%<\/text>';}\n        var gc='#e8e4dd',tT=[0,20,40,60,80,100,120];\n        for(var i=0;i<tT.length;i++){var tx=xP(tT[i]);\n            o+='<line x1=\"'+tx+'\" y1=\"'+mt+'\" x2=\"'+tx+'\" y2=\"'+(mt+ph)+'\" stroke=\"'+gc+'\" stroke-width=\"0.5\"\/>';\n            o+='<text x=\"'+tx+'\" y=\"'+(H-8)+'\" text-anchor=\"middle\" font-family=\"var(--vc-mono)\" font-size=\"10\" fill=\"#8a857e\">'+tT[i]+'\\u00b0C<\/text>';}\n        var vT=[2,5,10,20,50,100,200,500,1000];\n        for(var j=0;j<vT.length;j++){var vy=yP(vT[j]);\n            if(vy>=mt&&vy<=mt+ph){o+='<line x1=\"'+ml+'\" y1=\"'+vy+'\" x2=\"'+(ml+pw)+'\" y2=\"'+vy+'\" stroke=\"'+gc+'\" stroke-width=\"0.5\"\/>';\n                o+='<text x=\"'+(ml-5)+'\" y=\"'+(vy+4)+'\" text-anchor=\"end\" font-family=\"var(--vc-mono)\" font-size=\"10\" fill=\"#8a857e\">'+vT[j]+'<\/text>';}}\n        var pts='';for(var k=0;k<=100;k++){var tk=tMin+(tMax-tMin)*k\/100,vk=viscAt(tk);\n            if(vk<.8)vk=.8;if(vk>2000)vk=2000;pts+=xP(tk).toFixed(1)+','+yP(vk).toFixed(1)+' ';}\n        o+='<polyline points=\"'+pts+'\" fill=\"none\" stroke=\"var(--vc-accent)\" stroke-width=\"2.5\"\/>';\n        o+='<circle cx=\"'+xP(40)+'\" cy=\"'+yP(v40)+'\" r=\"5\" fill=\"var(--vc-ink)\" stroke=\"#fff\" stroke-width=\"1.5\"\/>';\n        o+='<text x=\"'+(xP(40)+8)+'\" y=\"'+(yP(v40)-7)+'\" font-family=\"var(--vc-mono)\" font-size=\"9\" fill=\"var(--vc-ink-secondary)\">\\u03bd\\u2084\\u2080='+v40+'<\/text>';\n        o+='<circle cx=\"'+xP(100)+'\" cy=\"'+yP(v100)+'\" r=\"5\" fill=\"var(--vc-ink)\" stroke=\"#fff\" stroke-width=\"1.5\"\/>';\n        o+='<text x=\"'+(xP(100)+8)+'\" y=\"'+(yP(v100)-7)+'\" font-family=\"var(--vc-mono)\" font-size=\"9\" fill=\"var(--vc-ink-secondary)\">\\u03bd\\u2081\\u2080\\u2080='+v100+'<\/text>';\n        if(vt>0&&isFinite(vt)){\n            o+='<line x1=\"'+ml+'\" y1=\"'+yP(vt).toFixed(1)+'\" x2=\"'+xP(tgt).toFixed(1)+'\" y2=\"'+yP(vt).toFixed(1)+'\" stroke=\"var(--vc-accent)\" stroke-width=\"1\" stroke-dasharray=\"4,3\" opacity=\"0.5\"\/>';\n            o+='<circle cx=\"'+xP(tgt)+'\" cy=\"'+yP(vt)+'\" r=\"7\" fill=\"var(--vc-accent)\" stroke=\"#fff\" stroke-width=\"2\"\/>';\n            o+='<text x=\"'+(xP(tgt)+10)+'\" y=\"'+(yP(vt)+4)+'\" font-family=\"var(--vc-font)\" font-size=\"10\" font-weight=\"600\" fill=\"var(--vc-accent)\">'+vt.toFixed(1)+' cSt @ '+tgt+'\\u00b0C<\/text>';}\n        o+='<line x1=\"'+ml+'\" y1=\"'+mt+'\" x2=\"'+ml+'\" y2=\"'+(mt+ph)+'\" stroke=\"var(--vc-ink)\" stroke-width=\"1.5\"\/>';\n        o+='<line x1=\"'+ml+'\" y1=\"'+(mt+ph)+'\" x2=\"'+(ml+pw)+'\" y2=\"'+(mt+ph)+'\" stroke=\"var(--vc-ink)\" stroke-width=\"1.5\"\/>';\n        o+='<text x=\"'+(ml+pw\/2)+'\" y=\"'+(H-1)+'\" text-anchor=\"middle\" font-family=\"var(--vc-font)\" font-size=\"10\" fill=\"var(--vc-ink-secondary)\">Temperature<\/text>';\n        o+='<text x=\"14\" y=\"'+(mt+ph\/2)+'\" text-anchor=\"middle\" font-family=\"var(--vc-font)\" font-size=\"10\" fill=\"var(--vc-ink-secondary)\" transform=\"rotate(-90,14,'+(mt+ph\/2)+')\">\\u03bd Viscosity (cSt)<\/text>';\n        o+='<\/svg>';el.innerHTML=o;}\n\n    function calculate(){\n        var vgVal=$('vc-vg').value;\n        var v40=vgVal?parseFloat(vgVal):parseFloat($('vc-v40').value);\n        var v100=vgVal?VG_V100[parseInt(vgVal)]||parseFloat($('vc-v100').value):parseFloat($('vc-v100').value);\n        var tgt=parseFloat($('vc-tgt').value);\n        if(vgVal){$('vc-v40').value=v40;$('vc-v100').value=v100}\n        if(isNaN(v40)||isNaN(v100)||isNaN(tgt)||v40<1||v100<0.5){$('vc-results').classList.remove('vc-visible');return}\n\n        var r=walther(v40,v100,tgt);if(isNaN(r.v)||r.v<0)r.v=0;\n        var vi=approxVI(v40,v100);\n        var pp=estimatePourPoint(v40,isNaN(vi)?90:vi);\n\n        \/\/ Operating range check\n        var rangeMsg;\n        if(r.v<5) rangeMsg='<span style=\"color:var(--vc-accent)\">\u26a0\ufe0f VERY LOW \u2014 Boundary lubrication risk. Consider thicker oil.<\/span>';\n        else if(r.v<13) rangeMsg='<span style=\"color:var(--vc-yellow)\">Marginal \u2014 Below optimal range (13\u2013100 cSt). Monitor wear.<\/span>';\n        else if(r.v<=100) rangeMsg='<span style=\"color:var(--vc-green)\">\u2713 OPTIMAL \u2014 Within 13\u2013100 cSt operating range.<\/span>';\n        else if(r.v<=500) rangeMsg='<span style=\"color:var(--vc-yellow)\">High \u2014 Above optimal. May cause churning losses.<\/span>';\n        else rangeMsg='<span style=\"color:var(--vc-accent)\">\u26a0\ufe0f VERY HIGH \u2014 Excessive viscosity. Check startup conditions.<\/span>';\n\n        \/\/ Dynamic viscosity (approx \u03c1 = 0.87 for typical oil)\n        var dynVisc=r.v*0.87;\n\n        $('vc-r-visc').innerHTML=(r.v>1000?r.v.toFixed(0):r.v.toFixed(2))+' <span class=\"vc-rcard-unit\">cSt (mm\u00b2\/s) at '+tgt+'\u00b0C<\/span>';\n        $('vc-r-vi').textContent=isNaN(vi)?'\u2014':'\u2248 '+vi+(vi>=120?' (excellent)':vi>=95?' (good)':vi>=80?' (fair)':' (low)');\n        $('vc-r-range').innerHTML=rangeMsg;\n        $('vc-r-A').textContent=r.A.toFixed(5);\n        $('vc-r-B').textContent=r.B.toFixed(5);\n        $('vc-r-ref').innerHTML=v40.toFixed(1)+' \/ '+v100.toFixed(1)+' <span class=\"vc-rcard-unit\">cSt (40\u00b0C \/ 100\u00b0C)<\/span>';\n        $('vc-r-pour').innerHTML='\u2248 '+pp+' <span class=\"vc-rcard-unit\">\u00b0C (estimated)<\/span>';\n        $('vc-r-dyn').innerHTML=dynVisc.toFixed(1)+' <span class=\"vc-rcard-unit\">mPa\u00b7s (at \u03c1\u22480.87)<\/span>';\n\n        $('vc-results').classList.add('vc-visible');\n        drawWaltherChart(v40,v100,tgt,r.v,r.A,r.B);\n\n        try{var u=new URLSearchParams();u.set('v40',v40);u.set('v100',v100);u.set('t',tgt);history.replaceState(null,'','?'+u.toString())}catch(e){}\n        saveHistory({v40:v40,v100:v100,t:tgt,vt:+r.v.toFixed(2),vi:vi,_summary:'\u03bd('+tgt+'\u00b0C)='+r.v.toFixed(1)+' cSt, VI\u2248'+(isNaN(vi)?'\u2014':vi)});\n    }\n\n    function saveHistory(e){var k='vc_history_'+SLUG;var a=[];try{a=JSON.parse(localStorage.getItem(k))||[]}catch(x){}e._ts=new Date().toISOString();a.unshift(e);if(a.length>10)a=a.slice(0,10);try{localStorage.setItem(k,JSON.stringify(a))}catch(x){}}\n    function loadURL(){try{var p=new URLSearchParams(location.search);if(p.has('v40')){$('vc-v40').value=p.get('v40');$('vc-v100').value=p.get('v100');$('vc-tgt').value=p.get('t');$('vc-vg').value=''}}catch(e){}}\n\n    $('vc-form').addEventListener('input',function(e){if(e.target.id!=='vc-vg')$('vc-vg').value='';calculate()});\n    $('vc-form').addEventListener('change',calculate);\n    document.querySelectorAll('.vc-preset-btn').forEach(function(b){b.addEventListener('click',function(e){e.preventDefault();$('vc-v40').value=this.getAttribute('data-v40');$('vc-v100').value=this.getAttribute('data-v100');$('vc-tgt').value=this.getAttribute('data-t');$('vc-vg').value=this.getAttribute('data-vg');calculate()})});\n    $('vc-copy-btn').addEventListener('click',function(){var t='Oil Viscosity\u2013Temperature\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\n'+$('vc-r-visc').textContent+'\\nVI: '+$('vc-r-vi').textContent+'\\nA='+$('vc-r-A').textContent+', B='+$('vc-r-B').textContent+'\\nPour point: '+$('vc-r-pour').textContent+'\\n\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\u2501\\nvibromera.eu';if(navigator.clipboard)navigator.clipboard.writeText(t)});\n    document.querySelectorAll('.vc-section-toggle').forEach(function(btn){btn.addEventListener('click',function(){this.closest('.vc-section').classList.toggle('vc-open')})});\n\n    var faqData=[\n        {q:'What is the Walther equation and how accurate is it?',a:'<p>The Walther equation (ASTM D341): log log(\u03bd+0.7) = A \u2212 B \u00d7 log(T). It produces a straight line on ASTM viscosity-temperature chart paper.<\/p><p>Very accurate for mineral oils from \u221220\u00b0C to 150\u00b0C. Less accurate for heavily additized synthetics, near pour point, or near flash point.<\/p>'},\n        {q:'What is Viscosity Index (VI) and what values are good?',a:'<p>VI indicates how much viscosity changes with temperature. Higher = more stable.<\/p><ul><li>VI < 80: Low (naphthenic base)<\/li><li>VI 80\u2013100: Normal mineral oil<\/li><li>VI 100\u2013120: Good (HVI or semi-synthetic)<\/li><li>VI 120\u2013160: Very good (PAO synthetic)<\/li><li>VI > 160: Excellent (multigrade, VI-improved)<\/li><\/ul>'},\n        {q:'What is the optimal operating viscosity range?',a:'<p>For most bearings and gears: <strong>13\u2013100 cSt<\/strong> at operating temperature.<\/p><ul><li>Below 13 cSt: boundary lubrication risk, increased wear<\/li><li>13\u201330 cSt: hydrodynamic bearings, high-speed gears<\/li><li>30\u2013100 cSt: general industrial gears and bearings<\/li><li>Above 100 cSt: may cause churning losses, high startup torque<\/li><\/ul>'},\n        {q:'How do I convert cSt to other units?',a:'<p>Kinematic viscosity: 1 cSt = 1 mm\u00b2\/s exactly.<\/p><p>Dynamic viscosity: \u03b7 = \u03bd \u00d7 \u03c1. Units: mPa\u00b7s = cSt \u00d7 g\/cm\u00b3. For typical oil at 15\u00b0C: \u03c1 \u2248 0.87 g\/cm\u00b3, so 100 cSt = 87 mPa\u00b7s.<\/p><p>SUS (Saybolt): roughly SUS \u2248 4.6 \u00d7 cSt (for cSt > 50).<\/p>'},\n        {q:'What is pour point and why does it matter?',a:'<p>Pour point is the lowest temperature at which oil still flows. Below pour point, wax crystallization makes the oil too thick to pump. It matters for cold-start conditions, outdoor equipment, and Arctic applications.<\/p><p>Mineral oils: typically \u221215 to \u221230\u00b0C. PAO synthetics: \u221240 to \u221260\u00b0C.<\/p>'}\n    ];\n    var fl=$('vc-faq-list');faqData.forEach(function(f){fl.innerHTML+='<div class=\"vc-faq-item\"><button type=\"button\" class=\"vc-faq-q\"><span>'+f.q+'<\/span><svg class=\"vc-faq-chevron\" viewBox=\"0 0 24 24\" fill=\"none\" stroke=\"currentColor\" stroke-width=\"2\"><path d=\"M6 9l6 6 6-6\"\/><\/svg><\/button><div class=\"vc-faq-a\"><div class=\"vc-faq-a-inner\">'+f.a+'<\/div><\/div><\/div>'});\n    fl.addEventListener('click',function(e){var b=e.target.closest('.vc-faq-q');if(!b)return;b.closest('.vc-faq-item').classList.toggle('vc-open')});\n\n    function renderFormulas(){try{\n        katex.render('\\\\log\\\\!\\\\log(\\\\nu + 0.7) = A - B \\\\cdot \\\\log(T_K)',$('vc-katex-1'),{displayMode:true,throwOnError:false});\n        katex.render('VI = \\\\frac{L - \\\\nu_{40}}{L - H} \\\\times 100',$('vc-katex-2'),{displayMode:true,throwOnError:false});\n    }catch(e){}}\n    function init(){loadURL();renderFormulas();calculate()}\n    if(document.readyState==='loading')document.addEventListener('DOMContentLoaded',init);else init();\n})();\n<\/script>\n","protected":false},"excerpt":{"rendered":"<p>Walther (ASTM D341) \u09b8\u09ae\u09c0\u0995\u09b0\u09a3 \u09ac\u09cd\u09af\u09ac\u09b9\u09be\u09b0 \u0995\u09b0\u09c7 \u09ac\u09bf\u09a8\u09be\u09ae\u09c2\u09b2\u09cd\u09af\u09c7 \u09a4\u09c7\u09b2 \u09b8\u09be\u09a8\u09cd\u09a6\u09cd\u09b0\u09a4\u09be \u0995\u09cd\u09af\u09be\u09b2\u0995\u09c1\u09b2\u09c7\u099f\u09b0\u0964 \u09af\u09c7\u0995\u09cb\u09a8\u09cb \u09a4\u09be\u09aa\u09ae\u09be\u09a4\u09cd\u09b0\u09be\u09af\u09bc \u0997\u09a4\u09bf\u09b6\u09c0\u09b2 \u09b8\u09be\u09a8\u09cd\u09a6\u09cd\u09b0\u09a4\u09be \u0997\u09a3\u09a8\u09be \u0995\u09b0\u09c1\u09a8\u0964 ASTM D2270 \u0985\u09a8\u09c1\u09af\u09be\u09af\u09bc\u09c0 \u09b8\u09be\u09a8\u09cd\u09a6\u09cd\u09b0\u09a4\u09be \u09b8\u09c2\u099a\u0995\u0964 ISO VG \u09b6\u09cd\u09b0\u09c7\u09a3\u09c0\u0964 \u09a2\u09c7\u09b2\u09c7 \u09a6\u09c7\u0993\u09af\u09bc\u09be\u09b0 \u09ac\u09bf\u09a8\u09cd\u09a6\u09c1 \u0985\u09a8\u09c1\u09ae\u09be\u09a8\u0964<\/p>","protected":false},"featured_media":0,"template":"","meta":{"ai_generated_summary":"","footnotes":""},"categories":[],"tags":[],"class_list":["post-100178","calculator","type-calculator","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/calculator\/100178","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/calculator"}],"about":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/types\/calculator"}],"version-history":[{"count":2,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/calculator\/100178\/revisions"}],"predecessor-version":[{"id":100927,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/calculator\/100178\/revisions\/100927"}],"wp:attachment":[{"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/media?parent=100178"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/categories?post=100178"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/vibromera.eu\/bn\/wp-json\/wp\/v2\/tags?post=100178"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}