Yes, you can even mix them together.
That's easy synthetic oil. Ill tell you why it sounds better
No, I would not recommend using synthetic in an engine this old. Use a good 10w40 conventional oil.
yes, but stick with it, same brand and same kind
80W 90 if using conventional. If using synthetic, 20W 50 will work. Also harley has Formula +.
Yes, anything mid 80's and up can be switched between conventional oil and synthetic oil. Anything older (that was around when zinc was found in oil, or when cork gaskets were used) should stick to conventional oil. It's actually federally mandated that conventional and synthetic oils be interchangable.
You can use synthetic, conventional, or synthetic blend. All are acceptable in a Dodge Caliber.
It is not a very god idea if that is what the manufacture requires, conventional will leave sludge and gunk in the engine.
It depends on the type of synthetic oil - Synthetic oils based on polyalphaolefin (PAO) / ester blends (e.g. Mobil 1) can be mixed with conventional oil - but you lose the benefit of the synthetic components the more you dilute it. You need to ask yourself why you want to mix it or why you need to use the synthetic oil in the first place - if you're using a synthetic to overcome a mechanical problem (e.g. insufficient heat transfer / oil cooling) then mixing with conventional oil is a waste as you won't fix the problem, same for synthetic gear oils if you are looking for heat transfer out of the drive train - only the "pure" oil will give the best heat transfer response. OTOH, if you are looking for extended oil drain interval, mixing synthetic 50/50 with conventional oil will assist.
If you are using conventional oil change the oil/filter every 5,000 miles. If you are using synthetic change it every 8,000 miles.
Non-organic farming, usually called conventional farming. uses synthetic pesticides and fertilizers. Unlike organic farming, GMO crops can be grown. About 95% of US crops are produced using conventional farming techniques.
Change the oil and filter every 5,000 miles if you are using conventional oil or every 7,500 miles if you are using synthetic oil.
You can use synthetic 75W-90 if you are using a gasket between the diff cover and the housing. If you are using RTV sealant with no gasket, use the conventional gear oil 80W-90. It seems the synthetic lube dissolves the RTV sealer.