Whats the best motor oil to use?

You have been using a particular motor oil and it has kept your motor running for 200,000 miles.

What in the world has changed that you think that motor oil isn't good anymore?!?!

Your motor is probably using some oil now. That has nothing to do with your choice of oil, it has to do with an engine that is finally starting to wear out. NO oil will perpetually stave off engine wear. That oil does not exist!

Keep using the Mobil 1. It has worked wonderfully for all of these miles and years. No other oil will work any better for you or your engine. When oil consumption finally exceeds 1 quart per 1000 miles, then you will have to decide whether you wish to rebuild your engine, replace it with a rebuilt block or trade this vehicle in on a new one.

PS: High mileage oils are just a bit thicker than other oils. That can cause other problems, especially with cold starts. Keep using what has worked for you in the past.

AMSoil is, but it's not worth it if you change the oil more frequently than the factory recommends, which a lot of Americans do. Really anything API certified is great, and if you're doing frequent changes the better oils won't be worth the extra cost. Castrol GTX is popular among enthusiasts. Dunno how you're telling when the oil is "done" but dark oil is a good sign: means the oil's detergents cleaned up and suspended the sludge. Doesn't mean the oil is done yet. Imperceptible microscopic wear particles and imperceptible chemical breakdown are. You need a lab to see that.

If you do get something fancy, Mobil 1, Royal Purple and Redline are all great too. Royal Purple might save 1/2 an mpg too, so I'd say for you AMS > RP > M1 > RL. But again for frequent changes costs will outweigh benefits.

And really if you want your motor to last a long time the most important thing is to change the coolant (any recommended coolant is fine) and thermostat (dealer thermostat only) every 2 years regardless of mileage, to prevent overheats, corrosion and a blown headgasket. Inspect hoses and belts regularly as well. Do all the service in the owner's manual if you want your car to last the long time, not only oil changes. It's a false sense of security, and better oil and frequent changes are only a falser sense of security. Something else will probably break instead.

Stay with what you have been using! Why change?

If you want to try the best conventional oil Castol GTX has been the top rated conventional oil since 2011 according to the API (American Petroleum Institute).

As far as synthetics go Amzoil has the number one spot Royal purple is next and then its a toss up for third with (Mobil 1, Penzoil Ultra, and Castrol Edge for quality).

As long as they are in the top 10 rated oils they are excellent choices, and since your truck was made well before the SN oil rating anything literally anything with the SN rating is a better oil than what was made when the truck was new!

So like I said I would not quit using what you are using now, but if you do change it won't harm anything at all!

a lot of people are going to say different things ! all i can tell you i used Pennzoil for over 25 yrs and i never had any trouble with the engines ! matter of fact Pennzoil is what i have in my 95 blazer right now and it runs good, but i use high mileage oil because it has over 200,000 miles on it ! i expect some will disagree with me but like i said i never had nothing go wrong by using Pennzoil !

You might try to increase the oil viscosity to 10W-30. Hang with Mobil1 Extended Performance. Corvettes have come from the factory with Mobil1 in the crankcase since 2006. All GM gasoline cars and trucks have come from the factory with Dexos 1 since 2011. All GM Truch diesels have come from the factory with Dexos 2 since 2011. Dexos 1 & 2 is a partial synthetic made by Rotella.

You absolutely should not use 10W-40 or 20W-50 in any street engine! The higher the viscosity of the oil, the slower the oil pump forces a SMALLER volume of oil to frictional surfaces during start-up. Not one American car or truck manufacturer ever recommended the use of 10W-40 or 20W-50 in ANYTHING!

If your "motor runs like new", I wonder what shape your transmission is in. Engine oil is only part of the list of fluids that need watching. It looks like you are able to use the web for this so doing a Google search on comparing the oils you mention shouldn't be a problem. I could tell you what I would use if I had your p/u but I'd get banned for soliciting. Needless to say - it would be the one that a poster misspelled.

I've read where people like to use heavier grades on old engines with a lot of wear. I was using 10w40 in my old car after 200,000, and I use 20w50 in it now

I like castrol, I always use that