This has been bugging me for a while, so thought I’ll write about it. I had long since heard about bigger motorcycles having trouble managing engine heat in heavy stop-and-go city traffic, even more so with air-cooled Harley-Davidson motorcycles.
They need air moving over the cylinder cooling fins at a minimum speed of 40-50 km/h to take away all the heat generated by the massive engines. Liquid cooled engines have it much easier as most typically have a radiator fan to help with cooling when the bike is stationary or at very low speeds. While the system is much like a car, most motorcycle radiators are much smaller than cars while their engines are not, so they can only cool effectively for a while when stationary or at low speeds, before the engine starts overheating.
With a Harley-Davidson or any other big air-cooled motor, you don’t have this grace period. They need a constant stream of air moving over them to keep them cool. So when you’re stopped with the engine running or crawling along at very low speeds, you’re effectively generating more heat than is being taken off the engine. The good thing about Harley-Davidson engines in this regard is that they are based on some very old (read tried and tested over decades) designs and are built with much higher tolerances than most typical modern day engines. So they let you safely go up to a significantly higher temperature range than you would be able to do safely on most modern motorcycles.
But even on a Harley, running a hot engine has it’s effects. The valvetrain sounds much louder than usual, so I’m not sure if it’s safe to run it at those temperatures. The problem on a Harley is that you don’t have an easy reference to know if you’re in a safe temperature range or not. Some suggest having an oil temperature sensing dipstick so you can keep an eye on the oil temperature. While that’s better than nothing I’m actually more interested in knowing the cylinder head temperatures as that’s where the heat source is, and also where most of the cooling happens from the air when you’re moving. The oil would typically still be very hot even though your cylinder heads might have cooled down after a short run at a decent speed. Unless you have an oil cooler.
I typically turn off my engine on long stops, be it a long red light or a completely stopped traffic jam. But when you’re in very slow (I mean walking pace) stop-and-go traffic for a long time, there isn’t much you can do. And unfortunately rush hour traffic in most parts of Bangalore is just that. I recently started work in a different office and most of my evening rides home are spent in just that kind of crawling traffic. I have tried quite a few alternate routes but can’t seem to avoid the traffic.
The other typical symptom of a Harley-Davidson engine overheating or close to overheating is knocking (aka pinging) when the engine is loaded under acceleration. And I don’t mean hard acceleration. When you just get going from a stop, the engine will knock a few times unless you give it a good amount of throttle or let the clutch out very gently and let it slip. I’m not used to giving it a lot of gas while getting it moving as there’s plenty of low-end torque. You’ll not stall and get going with just the slightest of throttle. And I hate slipping the clutch for obvious reasons. They have a very finite lifespan and are expensive to replace. And in heavy stop-and-go traffic, you’re engaging and disengaging the clutch a gazillion times anyway. Octane boosters have helped to a large extent but it still knocks now and then.
So as a result, each day I take my motorcycle to work, I end up giving it and myself a tough time on the way home.
What’s the solution? I don’t see any. I turn off the engine each time I know I’m going to be stopped even for half a minute. I also got myself a Shorai lithium iron-phosphate battery to prevent any battery issues arising from this. But when the traffic is moving along at a walking pace, there’s no way out. You can’t stop the engine and there is no way airflow to speak of to cool it. I have even contemplated switching to a liquid-cooled motorcycle at times. A Kawasaki Ninja 650 will probably be great. But I can only afford to have one motorcycle now, so that would mean selling the Harley for a good price, considering the various expenses I’ve incurred in the way of maintenance or upgrades. Something I’m not prepared to work on right now.
But it’s a lesson learnt. My motorcycle is not going to be air-cooled as long as I’m still in an Indian city. And I hope I can keep this Harley-Davidson going strong for as long as possible without any heat related damage.