I can't say if the engine heat will be different, never measured it. I run the now recommended 10W-50 motor oil these days. I have run 20W-50 in the summer (was all that was available at an oil change) with no issues. The only difference I could detect was motor noise. The top end engine clatter was toned down just a bit with 20W-50 compared to the 10W-40 that had been used previously.
