SOCIETY OFAUTOMOTIVE ENGINEERS, INC. TwoPennsylvania Plaza,NewYork,N.Y.10001 ViscosityStabilityof Polymer-Thickened Oils N. V.MessinaandH. H.RadtkeRohmandHaasCo. Automotive Engineering C1*(66ongre Detroit,Mich. January12-16,1970700053 Downloaded from SAE International by University of British Columbia, Tuesday, September 25, 2018700053 Viscosity Stabilityof Polymer-Thickened Oils N.V.Messina andH.H.Radtke RohmandHaasCo.ABSTRACT Acontinuous, highspeedroadtesthasbeenfoundtoaccu ratelyassesstheshearstabilityofmotoroilsunderalltypesof engineoperation. Ithasalsobeendemonstrated thatameth acrylatepolymerofsufficiently lowmolecular weightiscom pletelyshearstableundershearingconditions ofthehigh speedroadtest.Aroadshearstabilitysurveyofcommercial multi-graded oilshasshownthatsomeoilsfailtoproducethe expectedviscositydecreaseduetooiloxidation. Preliminary roadtestsindieselengineshaveshowntheshearstability lossesinpolymer-thickened oilssimilartothoseproducedin thegasolineengines. Shearstabilitystudiesinautomatic transmission fluidsby bothbenchandfieldtestshaveshownthatthisapplication is substantially moreseverethantheenginein shearing poly mericV.I.improvers CONSIDERABLE CONCERN hasdeveloped inrecentyears overtheviscosity-stability ofpolymer-thickened lubricants. Becauseoftheseverityofthestressesinvolvedinthecrank case,V.I.improvers maybeshearedtolowermolecular weight specieswhichresultsinareduction intheviscosityofmulti gradedmotoroilsduringservice.Accuratemeasurements of themagnitude ofthedecreaseisaprimeconcernoftheoiland automotive industries. Tothisendamultitude ofbenchtests havebeendeveloped. (1-9)*However,onlyintheenduse, thatisroadtests,cantherebecompleteconfidence inthere sults.Theprimaryprobleminsuchanapproach isthegreat lengthoftimenecessarytoaccumulate data.Itispossibleto circumvent thisproblem,however,ifhighspeedroadtestsare used. HIGH-SPEED ROADTESTS Aconsiderable amountofworkhasbeendoneonthemea surementoftheviscositystabilityofpolymer-thickened motor oilsundertheconditions ofa2000milehigh-speed roadtest. (1,2)Thesetests,whichsimulatedturnpikedrivingcondi tions,haveshownthattheoilsarereducedinviscosityuntila minimum isreachedbetween1000and2000miles.Fig.1 showstheviscositychangeinatypicaloilasafunctionof mileageduringahighspeedtest.Sincefueldilutionisavari ableamongcarsandtypesofdrivingandisacharacteristic of singleandmultigraded oilsalike,accurateassessment ofthein fluenceofthestabilityoftheV.I.improvercanonlybe achievedindilution-free samples.Ourmethodforremoving fueldilutionfromtheusedoilsamples(Appendix) hasbeen showninourworktobecompletely effective. Newoilsampieshavebeentreatedbythismethodandfoundnotto changeinviscosityindicatingthattherearenolightendsre movedfromtheoilduringtheprocess.Moreover, itwasalso established thatthebaseoil,eitherwhentreatedwithonly zincdialkyldithiophosphate orwhentreatedwithacomplete additivepackage,hasshownessentially noviscositychange duringthe2000mileroadtest.Thesedata(Table1)provided abaselinefromwhichwecouldassumethatanyviscosity changeinthepolymer-thickened oilswasactuallytheresult oftheshearmgeffectsonthepolymer. Inordertoknowtheusefulness ofthe2000milehighspeed test,itwasimportant toknowtherepeatability ofthetestina singleengine,thevariationinshearingseveritythatcouldexist inagivenmakeofengine,and,finally,theshearingseverity variations thatmaybeencountered inenginesofdifferentsize. Toanswerthesequestions, weusedareference oilformulated withahighmolecular weightmethacrylate polymerwhich wouldbesensitivetosmalldifferences intheshearingstress thatwasappliedtotheoil.Therepeatability ofthe2000mile roadtestinthesamecarwasfoundtobeexcellent. Basedon theequivalent ofsixpairsofduplicateruns,thestandarddevi ationassociated withrepeatrunsoftheoilonthesamecar was0.13cSt.at210F.(Table2).Thevariationinshearing severityfor11testsinvolvingsixcarsofthesamemake(327 CIDengine)wassomewhat greaterwithacorresponding devi ationof0.33scSt.at210F.For10European carswithen ginesranginginsizefrom45.6-122CID,the