Synthetic oil?
 

So I was thinking about switching to synthetic oil because a good amount of people around me are. First off, what are the pros and cons? And Most people I see using synthetic are lower milage cars. My 1997 GMC Sierra is just under 200k (199,637) Should I make the switch? I was also thinking about running premium fuel, I think it's 91 octane, what will that do?

Well with a stock engine, you don't need 91 octane. The only thing 91 octane is good for, is an engine that has pre-detonation due to higher compression, advanced ignition timing, or an engine with lots of carbon in the combustion chamber. Don't waste your money, these trucks suck enough expensive 87 octane gas as it is lol

Also the synthetic thing is kinda up to you, but for me personally, conventional/synthetic blend every 3K works wonders. I honestly wouldn't spend the money on full synthetic oil. I see chrysler 3.3L V6 engines that have been running 5w30 synthetic blend with napa oil filters since new go 300,000+ miles on the original engine. These are cars that one of my boss's account holders brings to us for their oil changes. Mind you, these vans also go 5K+ on their oil changes.

Just take care of your engine, and it should last you. Use a quality oil filter, and change your oil and you'll be fine. I am no a believer in going 10K-30K on the Amsoil stuff that they sell. I just don't trust it .. the oil still gets dirty, it's just that the additive packages will survive that long in your engine. So ... considering your oil still gets dirty from carbon and gasoline and whatever else makes it into the crank case, I really wouldn't go more than 5K on any oil you put in there. That's just me, but I'm not a believer.

So that's my two cents. It doesn't mean that it's all 100% sound, but there it is!

I run 100% synthetic oil in my Duramax and my wife's 6 cylinder V70 Volvo The good part? Engines run some what quieter. Provides better protection on cold starts.
Can go longer between oil changes
The bad part? The syn oil is a little more expensive per Liter.

I hope this video will help you answer your Regular fuel vs Premium fuel

Need more vehicle and location details to make an informed decision.
Will you be towing through death valley in the summer, sitting outside in northern Canada in the winter, does it have a holley procharger? etc.

So long as your engine seals are in good shape, running synthetic oil would be fine for your mileage on that motor. One thing I do recommend is doing an engine flush before replacing the dino oil with synthetic. I run Amsoil in my Dodge, and I won't run anything else.
Scott

Thanks everyone for the feedback! I think I'm just going to change the oil around every 3k miles. The truck was given to me and theres a little stick that says "change oil at 185k". My odometer reads... 201,XXX. Thank god I have my sights on a new motor or the near future anyway.

I think it'll be fine. If your worried about it, put 1/4 to 1/2 of a bottle of seafoam in the crank case and drive for 100-200 miles with it in there then change your oil.

Also maybe we could have pictures of the damaged areas? I just searched for and found pictuers of your truck and that thing looks pretty clean! Mine is already suffering from bad cab corner rust and the wheel wells are getting pretty bad, but just how bad are the areas you are talking about? Anything is fixable.

And how exactly do I go about doing that..?

I managed to snap one picture of the spot i was most worried about before my sister had to borrow it (her car is getting a new motor)

Those picture are about 9 months old and don't show the full extent of things I'm afraid haha. I'll get some more asap.

How do you seafoam it??? Oh, sorry. Seafoam is an engine/fuel system cleaner that removes varnish from injectors/cab jets and engine sludge/grime out of your engine. When I mentioned the "crank case", I just meant pour it into your engine oil. Like literally where you add oil in the valve cover. That valve cover hole drains down into the top of the cylinder head and then drains down into your oil pan/crank case area. When the seafoam is in there, it'll get sucked up through your oil pump and dispersed through your oil galleries and every part of your engine that gets oil.

So the idea is that the seafoam will clean the inside gunk/vanish/sludge off the internal parts of your engine and allow them to be returned to the oil pan/filter. Which is why you really don't want to run your oil for very long when it has seafoam in it because it'll continuously clean. And then you just end up with dirty oil ... which is not good for bearings.

So 15K on an oil change really isn't all that bad. Absolutely no reason to get a new engine ... just change the oil asap.