Question about 2005 Harley Davidson FLSTC - FLSTCI Heritage Softail Classic

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Chanmge from conventional 20W50 oil to synthetic

Change from conventional 20W50 oil to synthetic oil on 2005 Harley softail?

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Not a problem, I've done it on my '94 model Wide Glide. Your bike probably came from the factory with synthetic oil in it. Harley developed their Syn3 20W50 oil and the bikes are shipped with the stuff in all three compartments, the engine, the primary, and the transmission. Just check the manufactures website to make sure whatever oil you decide to use meets Harley's specs.

Good Luck

Posted on Jul 16, 2010

Testimonial: "Thanks, but what about the oil in the cases?"

  • wd4ity
    wd4ity Jul 23, 2010

    Basically, there is no oil in the cases. Oh sure, there's a little but a Harley engine is a "dry sump" engine design. In this design, the oil for the engine is carried in a remote oil tank. The oil is pumped to the engine, lubricates what it is intended to lubricate, and then is scavenged out of the engine back into the oil tank. There is no oil reserve in the engine itself like there is in a Japanese engine. It's like the engines they use in NASCAR racing. They use the 'dry sump" engine so that in the event of a blown engine, there isn't as much oil put down on the track. So, If your bike holds three quarts of oil, there may be only a half pint of oil in the engine at any given time.

    As for changing from petroleum based oil to synthetic oil, the oils of today are completely compatible where in the past this may not have been true. No problem, just start using synthetic whenever your next oil change is due. The only downside to it besides the cost is synthetic oil has a tendency to leak more for some reason. I have no idea as to why but it does. If you have a small leak with petroleum based oil, odds are it will be worse with synthetic oil.

    Good Luck


  • andandrew
    andandrew Jul 24, 2012

    Petroleum is refined to make conventional motor oil. Even after the process is finished paraffin wax is left behind. This when over heated turns to varnish. It fills in the gaps and holes in your worn out casket- it also blocks your oil lines and causes oil to effectively stop flowing at cold temperatures. Synthetic oil is very detergent, cleaning the vanish and sludge left behind by conventional oil. So that small leak that was kept in check by the gunk conventional oil closed up gets cleaned up and opened when you use synthetic oil. It's not that synthetic oil makes your engine leak, it's that your gasket probably has been held together by gunk for a long time and now it's finally getting cleaned out BUT so is the rest of your engine and it thanks you for it. Just change your gasket and enjoy!



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