Having Issue with Measuring/Draining Engine Oil on your Harley?


What we hear:

Very often we have the following comments/questions:

  • How come there is so much oil level difference between a cold or warm engine? I did not know that the oil expands that much!
  • When I drain the oil, there is not much coming out and it just takes about 1 quart or less to refill it; is anything wrong on the Harley documentation?


What Harley says:

Harley says that you should run the engine for a couple of minutes before draining the engine oil and that you should measure the oil level when the engine is hot a minute or 2 after you stopped the engine. A lot of people believe that as in many cars the need to run the engine before draining the oil is just to have the oil more fluid so that it is easier to drain. Harley does not clearly say why you should run the engine before checking the oil level or before changing the oil.



Effectively, the oil does not expand that much between cold and hot. Also the Harley documentation is pretty accurate about the amount of oil that should be drained and later added while changing oil.

These Harley engines are “dry sump” engines. This means there should be no oil accumulation on the lower end of the engine. This is true when the engine is running as these engines have in fact two oil pump, one pressure pump to distribute oil under pressure to the critical engine sections and a scavenge pump to take the oil from the bottom of the engine and put it back in the oil tank.

Since on most of these bikes, the oil tank is located higher than the engine, the oil has a tendency by gravity to slowly flow backward from the tank to the engine when it is not running. So if you drain the oil tank in this condition you will only get a small part of the engine oil. Also if you fill the oil tank you now have too much oil in your system with the risk of oil tank overflow when the engine is restarted.

In summary, when you need to measure the oil level or change the oil, it is essential that you run the engine for a couple of minutes before the operation in order to have all the oil back on the oil tank.