Does a Harley Davidson run and perform better in colder weather than running in hot weather?
It depends. The newer EFI bikes come with factory ignition curves and lean pulse width modulation for the injection to meet EPA regulations. With lower octane fuel they can detonate a bit when they’re hot. It’s an easy fix. Some of the really old Sportsters with wet clutch conversions would heat up and the clutches could drag. The Ironheads didn’t dissipate heat very well and would run hot in stop and go traffic on hot days. Aftermarket oil coolers and synthetic oil take care of it. Many drag cars use coolers to cool the fuel. They’re doing everything they can to gain a tenth or even a hundredth of a second. On a street bike it’s not gonna make much of a difference. Air-cooled engines obviously run cooler with air moving over the cooling fins but the newer aluminum heads do a decent job of dissipating heat even at high ambient temps and synthetic oils help as well. The carbureted bikes generally run better when they’re warm. It’s kinda refreshing to see a legit question from you Bart.
While not a Harley-Davidson owner, I did own a 1978 BMW. While the engines did not get as hot during the summer due the engine configuration compared to a friend’s HD, it did run better when the temps headed south. Also my feet never got cold when the temps were below 40 degrees F. A friend has a private pilot’s license and flies a four seat Piper 180 Cherokee. He really prefers flying during the winter. Engine runs so much stronger and cooler. Denser air helps a great deal. I am aware an aircraft engine runs a carb and magneto while new bikes are fuel injected with ECUs. Bart, this is a good question.
Neither one of my run better in the cold than in the heat. Here I often ride in 35 to 40 degree weather and both of my bikes spit and sputter at idle and low engine rpm. It gets worse if it’s damp or wet out. A hot day here is 75 degrees and they run just fine and I’ve had them to Florida, Texas, Arizona and over the south and never had an over heating problem except during drill practice on very warm days when the team is doing extended slow speed drill practice.
It is not due to the temperature that every internal combustion engine works better in colder denser air. Simply put, there is more oxygen in the denser air and more oxygen means bigger bangs, the weather becomes like an atmospheric pressurised airbox. All engines, even liquid cooled engines, expend nearly 70% of the energy they produce as heat – they are a series of controlled explosions after all – that means that only 30% goes towards kinetic energy, even that is further dissipated through more heat loss by friction.
