Does synth's base oil make engines run cooler than a dino's base oil in the same engine under normal conditions? I suspect this will turn out to be a hot topic as I for one don't believe that you'll not see much if any noticable difference in temps from changing over from a dino to a synth. Yet I hear way too many claiming it does. Well now is the time to show us non believers how it does. In the many oil changes and different oils used, I have never seen an instance where the synth base oil has made any difference in temps, at least not no 10 to 20degs as some claim. I ran across an engineer that made some interesting comments and totally agree with this so here is a copy of his post.... I have done a bit of testing here, with both head temp and oil temp gauges in my car for thousands and thousands and thousands of miles over every terrain I can think of under every loading condition I can imagine. All my testing was done in the late 1990's and early 2000's - not the 1970's. I've used conventional oils, hydrocracked petroleums (i.e. legally "synthetic," but not really synthetic), and true synthetics in aircooled vehicles. Effect on head temperature? ZERO. Effect on oil temperature? Depending on your choice of oil, you may notice no difference or a very slight drop in oil temperature. Now, when you are pushing the limits and holding a highish rpm for a long period of time, your oil temp will skyrocket unless you have some nice coolers. I've baked conventional oils before... the smell is unmistakable :-). I have been unsuccessful at baking a synthetic oil. Even when running with no oil cooler and sustaining a 275F+ oil temperature, I couldn't even get a hydrocracked petroleum oil to bake. Oil pressure didn't die either. These findings are very helpful to us heavy-footed fellows :-). Take care, ------------------ Shad Laws LN Engineering Now interesting thing here is unless an oil is pushed to extremes, like what he had done, you wont see any real differences. Only when you need an oil that can withstand heat for long durations will a synth or even a blend will give you the performance differences. But as for lowering the operating temp under normal conditions, I have yet to see this. I have taken temps with motors and bearings alike having changed to full synths' and have not seen this to make the difference. I'd be interested to see how well the newer SL grades would hold up in comparision now. Where the difference is, the additive package more so than the base oil itself.