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


Asked by Apr 04, 2012 at 12:04 AM about the 1995 GMC Sierra 1500 K1500 SL 4WD Extended Cab SB

Question type: Maintenance & Repair

1995 gmc sierra z71 5.7 right now no leaks. i want to keep this truck for a long time,please help

10 Answers


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

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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

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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.

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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.

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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.

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