Before anything, you should concern yourself only with putting oil into where you see the cap 'engine oil'. That will save you from your burden of choice.
I like to advise people changing oil to use a particular safe additive, from a reputable seller, called LUCAS oil stabilizer. If you substituted 20% of your oil for this additive, it would aid your oil in adhering to engine parts longer than regular oil. On the vehicle startup, especially in the cooler weather approaching, this will be very helpful as the startup of a vehicle is the most damage done to an engine.
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Here is a bit of knowledge on oil viscosity. This webpage was created by AMSOIL for the express purpose to explaining the oil differences (and if you are using regular oil, it may be best to stay with regular because once switched you don't want to return to the other):
http://www.motoroilinfo.com/which-30-wt-...
Pay close attention to the paragraph underneath the photos. Here it is, for your viewing pleasure:
AMSOIL 0W-30, 5W-30 and 10W-30 synthetic motor oils are ALL 30 weight oils. The answer is that ANY one can be used regardless if your vehicle owners manual says to use, for example, a 5W-30. "W" means winter. In winter weather the 0W oil will flow like a 0W oil, and the 5W will flow like a 5W oil and a 10W will flow like a 10W oil just until the engine warms up. In order to understand the differences one has to first understand that the numerical values given to these various weight oils are strictly empirical numbers. For example, 0W does not mean that the oil has no weight. That is one of the reasons why we say it is strictly an empirical number.
For the word 'empirical':
http://en.wikipedia.org/wiki/Empirical
