How do hydraulic flat tappet lifters fail?

I hate to beat a dead horse, but I was reading an oil viscosity chart, and I think I may be running the wrong oil. This chart gives suggestions according to bearing clearances, and my main bearing clearances were .002". According to the chart, I should run 20 weight or 30 weight. I was running 40 weight. Would that cause an oiling problem at higher RPMs or higher temps?