do i dare put 5-30 snythetic blend in a truck with 200,000 miles on motor? or will it start leaking thru its gaskets

it's never too late to run synthetic, and why stop at blend? go full syn. pure myth that it will leak. Amsoil Mobil1 Pennzoil Ultra All top synthetic oils

my 95 sierra 5.7 gets 5w-30 castrol high mileage. it's running strong over 270k. it's a partial synthetic blend. definitely a must for a high mileage engine

stick with the high milage, it has additive in it to recondition seals and prevent/slow/stop small leaks. high milage is not a synthetic of any type. its a conventials still meeting/exceeding all manufacture spec. it just has a slightly diff additive package. few more rust inhibitor, conditioners and cleaners.

Chris is right, high mileage is the way to go. But castrol high mileage is a part synthetic oil.

Sythetic oils are very good. They have better shear stregth which is good when bearing pressures are high (like desert racing with high perf motors) and they excell in severe cold too (better flow) If you're like 99.9% of the people out there and use the engine for normal daily driving, it really doesn't "add" anything to the picture. Its like burning premium fuel in an engine that's not designed for it - it makes you feel better but achieves nothing. Yes, its great oil but unesessary in most circumstances. Its much more important to change it regularly. And oh ya, it has nothing to do with leaking - in fact, if you don't have any leaks as you say, I would even stay away from "high mileage" oil as it contains chemicals that actually attack the seals swelling them in the process and slowing small leaks. In the long run, it degrades them. I have 230,000 on the same engine you describe and have never used synthetic or any additives. Just regular oil/filter changes.

I used castrol high mileage for a long time. You can't go wrong with it. But I now swear by Royal Purple. I have a 91 Sierra 350 with 210 thousand and since going to purple my mileage has gotten so much better it's insane. I even talked my dad into using it and he was a dihard castrol guy. He's been using it in his 02 2500 HD and his improved gas mileage blew his mind. It costs alittle more but it's so worth it. Hell I've told friends to try it and if they didn't see improvement I'd pay for the next change. I haven't paid yet.

Hi I have a 2500 had work truck that has 320000 what type off oli should I be useing on it

Use what is recommended by GM for that year/model. High mileage oils have some additional additives but also include ones that may damage good seals so unless you have leaks I would stay away from those. It most important to just keep up with regular oil and filter changes. There is no magic or mystery in oil. Just use the correct one and change it when you should.

I have a 2000 gmc 1500 with 292,000 miles what should i use

Use what the manufacturer recommends. They have a lot of knowledge and testing data to back it up. Its waaaaay more important to change it regularly and use a good AC Delco or Wix (NAPA) filter. Synthetics are good, but of little value on this engine unless you race it or are squeezing every mile out of the oil, like a fleet truck.

on a high mileage motor the bearing clearances are gonna be greater than when it was new. with this being said it wont hurt rather help if you step up to a heavier weight oil. you have to take a few things into consideration. 1. climate. if you live in the south where there is less fluctuation in temp. i would say use either 10w30 or 10w40. remember these engines have been around in their basic design since the fifties and when they were developed the automotive industry didnt even have multi weight oils or detergent oils for that matter. and the typical oil used was a straight weight 30 or 40 weight. non detergent. if you are in colder climates or an area that has dramatic temprature fluctuations between seasons then you might want to run 5w30 in winter and 10w 30 or 40 in summer. the thicker oil will give you a thicker film on the bearing surfaces acting like a cushion between the surfaces keeping the operating temps down and decreasing valve train noise typical on american v8's with high mileage. My local machine shop says to use 10w40 exclusively. he builds drag engines and runs nothing but 10w40 or either 15w40 rotella diesel oil. The reason is as stated earlier. diesel oil has a higher content of zinc that also acts as a cushioning agent. you can buy zinc additive by itself and engine builders use it to help break in camshafts and to keep from flat spotting cam lobes during the break in period. also diesel oil has a high detergent additive package that will keep the engine cleaner. you might notice a slight drop in gas mileage due to the thicker oil but the engine can handle it no problem and you will notice a jump in oil pressure. 2. A good filter is key. Im gonna get an arguement on this one probably but i stay away from AC Delco filters. i have seen the differences between "factory" filters and aftermarket filters. just cut one open. lets just use Wix as an example...the wix filter when cut open has more pleats in their filter media and an anti-drain back valve that keeps the oil in the filter after the car is shut off. without the valve the oil will drain back into the oil pan.so when it is started back its running for that second or two without full oil pressure waiting on the oil pump to pull the oil back from the pan and fill the filter before it goes to the top of the engine. Burst strength is another advantage. a premium filter will use a thicker shell and a double crimp making a stronger filter. you can tell by taking your filter and squeezing the sides of the filter. a good filter will have hardly any give when you squeeze the sides of the filter. i have had cheaper filters that i could squeeze and literally dent the filter. but what do i know. my 1990 c2500 has 476 thousand miles on the original motor. puffs a tiny amount of smoke after sitting overnight but still keeps 30 + pounds of oil pressure at operating temp and when i run premium gas she feels like she has 50k on her. compression is even hovering around 100 psi with less than an 10% variation between any of the cylinders. keep the pcv system clean and enjoy a true american marvel of engineering

Okay guys I have a 1997 gmc sle 5.7L and it's has 157000 something miles on it and I got the oil change once in last November and I just ran out of oil like I was using high mileage something can't remember but now I'm using sethyic is it bad for it?

what is the best oil for 1992 chevrolet truck(RV) P30 engine. I just changed with sae 5/30 full synthetic motor oil. it seems to run smooth. but I am in doubt. My mechanic told me I should put 15/30 thicker motor oil. I am confused if I should switch back to conventional motor oil ?