Shortly after I bought my first Honda EU2000i I tried starting the Coleman 13.5K BTU A/C I owned at the time but found the results were hit and miss, working one time but not another. Another forum contributor suggested that switching the dino oil to synth just might make a difference, citing his own success with it. I thought "Yeah right, like that will make a difference!" but I had little to lose by trying it so I dumped the dino oil change I had just done and put in Mobil 1. Without any other changes the A/C started right up every time ... couldn't believe it would make such a difference! We now have a different trailer with a Dometic Brisk II 13.5K BTU A/C and a different EU2000i so before even trying to start the A/C the first thing I did was dump the genset's dino oil in favour of Mobil 1 synth ... and again the A/C starts every time. I've since added a hard start cap to the A/C to further ease that initial load the genset has to deal with but there's little doubt that running synth oil really does help. :B