To use or not to use is the big question when it comes to using synthetic oil. There should not be any question about using synthetic oil in your engine. With a few exceptions, you can’t afford it, have a ton of miles on your engine anything in excess of 90K, your engine is using or leaking oil. Cost is always a concern in today’s economic situation and it is critical to change your oil on a regular basis. Synthetic will only save you $ if you put on a lot of miles but it will provide superior lubrication and prevent cold start wear on the engine. Any engine with a lot of miles is going to have a problem when switching it cleans too much of the crud out of the engine causing problems if you have serviced the engine regularly you may get by with it but I hesitate to risk it. I switched my pickup at 60K and had no problems but it has had regular oil changes but it does have a lot of in town miles. I have since switched it back as I don’t drive it much and I feel it is more important to change it on a regular time table. If your engine is using or leaking oil it will get worse, synthetic oil tends to shrink the seals slightly and it clinks to engine parts mainly the cylinder walls allowing loss of oil. If your loss is less than a quart between changes then go ahead and switch. The engine that uses some oil between changes is going to last longer because lubrication is improved.There are 2 types since separated into 4 groups, the first developed by Mobil in the seventies is PAO. The second is unconventional base oils or UCBO which most premium oils are today. There are several variations, Amsoil, Royal Purple are true synthetics Castrol is syn tec.These I stay away from not for any reason I just prefer the UCBO oils. Unless you are a chemist or a lubrication nerd the only thing you have to remember is to any brand name is OK just stay away from the bargain basement brands also stick with one that is available in most markets. Semi or partial synthetics are a waste of $ they usually contain less than 10% synthetic stock. They will help but to a very minor extent. The major advantages of synthetic are longer change intervals, cleaner engines, improved lubrication and less cold start wear. At -40 you can definitely tell the difference if you have synthetic in the crankcase. Talk to any Tech about oils and you will get as many opinions as you will on blonde’s brunettes or redheads. So go with what you can justify $ wise what is available locally, I went to the same shop for a number of years they had great oil change specials and used Chevron, which I had been using, but they have been overfilling about a quart lately so I don’t know what I am going to do. I may switch back to synthetics and start doing my own changes, cheaper when I do it myself.