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

5

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

6 Answers

345

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

1 out of 1 people think this is helpful.
1,185

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

1 out of 1 people think this is helpful.
735

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.

1,185

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

400

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.

3 out of 3 people think this is helpful.

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.

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