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

8 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

1 of 1 people found this helpful.

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 of 1 people found this helpful.

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.

3 of 3 people found this 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.

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.

Your Answer

Add photo

Related Questions

Sierra 1500

Looking for a Used Sierra 1500 in your area?

CarGurus has 68,701 nationwide Sierra 1500 listings starting at $1,800.


Search GMC Sierra 1500 Questions

GMC Sierra 1500 Experts

#1 dragonflyoffshore
Reputation 5,230
#2 John Saffrahn
John Saffrahn
Reputation 3,640
#3 Glenn Clingenpeel
Glenn Clingenpeel
Reputation 3,330
View All

Related Models For Sale

Used Ford F-150
2,171 Great Deals out of 195,112 listings starting at $290
Used Dodge Ram 1500
418 Great Deals out of 10,945 listings starting at $1,000
Used Toyota Tacoma
516 Great Deals out of 43,167 listings starting at $1,995
Used GMC Yukon
423 Great Deals out of 20,393 listings starting at $1,495
Used Chevrolet Tahoe
598 Great Deals out of 32,881 listings starting at $1,500
Used Chevrolet Camaro
351 Great Deals out of 31,370 listings starting at $2,500

Used Cars For Sale

2017 GMC Sierra 1500 For Sale
92 Great Deals out of 44,500 listings starting at $23,368
2016 GMC Sierra 1500 For Sale
89 Great Deals out of 3,512 listings starting at $17,670
2015 GMC Sierra 1500 For Sale
95 Great Deals out of 4,251 listings starting at $16,291
2014 GMC Sierra 1500 For Sale
93 Great Deals out of 4,195 listings starting at $13,995
2013 GMC Sierra 1500 For Sale
55 Great Deals out of 1,945 listings starting at $8,500

Content submitted by Users is not endorsed by CarGurus, does not express the opinions of CarGurus, and should not be considered reviewed, screened, or approved by CarGurus. Please refer to CarGurus Terms of Use.