Oil Question? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

mcashman · 02-03-2009, 05:50 PM

I just bought a 1971 c20 with a factory 400, 83,000 original miles. Does it matter if I use 10w-30, 5w-30, or 10w-40? I had a 1970 with a 350 and I always used 10w-30. Just wondering if it makes much of a difference?

**1970cstblazer** · 02-03-2009, 07:10 PM

I would use a quality 10w30 oil with a bottle of GM EOS to provide your engine critical zinc that is no longer provided in regular oils. The zinc is critical in engines using flat tappet cams and regular rocker arms.

I personally use Shell Rotella 15w40 diesel oil in my '72 402. The diesel oils still have decent amounts of zinc.

68gmsee · 02-03-2009, 07:39 PM

Since you're in cold country, I'd almost go with 5W 30 for the winter. But it all depends on the condition of your engine.

Remember that on these engines 83,000 miles was considered high mileage unless they were overhauled. Doesn't mean that they were scrap but usually at 50K to 60K the bearings, rings and valve guides might loosen up enough to require a higher weight.

Here in Texas where the weather is pretty mild, I stick to 10w30 oil for most use and go up to 20w 40 if the engine is high mileage.

tim21391 · 02-03-2009, 08:08 PM

i run castrol gtx 10w30 in all my vehicles

big_al_71 · 02-03-2009, 08:16 PM

cold climate 10w40
hot climate 5w30

that is what we do

Camper Power · 02-03-2009, 10:31 PM

i let the weather decide what weight im gonna use, seeings how your in montana and we are in the beginning of febuary, i would run 5w-30. im not really an expert on high milage stuff but i know when it comes to climate, u gotta up here in Canada. 5w in cold weather makes it easier for your starter to turn your engine compared to 10w oils. other then that theres no difference, but like i said im not an expert on high milage engines.

Longhorn Man · 02-05-2009, 05:47 PM

don't pour in the whole bottole of EOS on one oil chainge, that is way too much. 1/4 bottle is plenty.
Pretty much all the diesel oils now have LESS zink than the gas oils do, so no point in that.

02-03-2009, 05:50 PM	#1
mcashman Registered User Join Date: Oct 2008 Location: Bozeman Montana Posts: 21	Oil Question? I just bought a 1971 c20 with a factory 400, 83,000 original miles. Does it matter if I use 10w-30, 5w-30, or 10w-40? I had a 1970 with a 350 and I always used 10w-30. Just wondering if it makes much of a difference?

02-03-2009, 07:10 PM	#2
1970cstblazer All stock and staying that way Join Date: Jul 2003 Location: Elkland, PA Posts: 1,682	Re: Oil Question? I would use a quality 10w30 oil with a bottle of GM EOS to provide your engine critical zinc that is no longer provided in regular oils. The zinc is critical in engines using flat tappet cams and regular rocker arms. I personally use Shell Rotella 15w40 diesel oil in my '72 402. The diesel oils still have decent amounts of zinc. __________________ 1970 K/5 Blazer CST 4WD, Medium Bronze, 93k ACT. miles, 350, 4 speed, rear positraction, 16.5" x 8.25" HD wheel option, tilt, tach, vacuum, AM/FM, manual throttle...Dad ordered and purchased new 4/70. Currently frame off restoration finally getting close to completion.. 1972 Cheyenne Super 20 2WD, DK Blue/White, 90K ACT. miles, 402, TH400, 4.10 open, tilt, tach, vacuum, A/C, AM/FM, manual throttle.. A mostly original paint never rusted Texas survivor... 2017 Sierra 1500 SLT 4WD, Black, 45k miles, 5.3, 6L80E, 3.42 LS, 20" polished wheels, everything but moonroof and 6.2... 2019 Canyon SLT 4WD, White, 62k miles, 3.6, 8L45, 3.23 LS, 18" wheels

02-03-2009, 07:39 PM	#3
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Oil Question? Since you're in cold country, I'd almost go with 5W 30 for the winter. But it all depends on the condition of your engine. Remember that on these engines 83,000 miles was considered high mileage unless they were overhauled. Doesn't mean that they were scrap but usually at 50K to 60K the bearings, rings and valve guides might loosen up enough to require a higher weight. Here in Texas where the weather is pretty mild, I stick to 10w30 oil for most use and go up to 20w 40 if the engine is high mileage.

02-03-2009, 08:08 PM	#4
tim21391 Registered User Join Date: Jul 2007 Location: Salina, Kansas Posts: 1,998	Re: Oil Question? i run castrol gtx 10w30 in all my vehicles __________________ 1972 C-10...402/400..flowmaster 40 series 1967 Mustang 347 stroker/C-4 1966 Mustang 289/3-speed 2013 Mustang V6/6speed w/300 ponies I may be 23, but i sure do knows 67-72s are sexy! Its not MPG its smiles per gallon! build started 11/25/08 build thread: http://67-72chevytrucks.com/vboard/s....php?p=2993796

02-03-2009, 08:16 PM	#5
big_al_71 Registered User Join Date: Jun 2008 Location: South Florida Posts: 11,375	Re: Oil Question? cold climate 10w40 hot climate 5w30 that is what we do __________________ Get your facts first, and then you can distort them as much as you please!!!!!. Sylvester's build thread >>>http://67-72chevytrucks.com/vboard/s...ht=big+rebuild

02-03-2009, 10:31 PM	#6
Camper Power Registered User Join Date: Feb 2008 Location: Grande Prairie Alberta Posts: 261	Re: Oil Question? i let the weather decide what weight im gonna use, seeings how your in montana and we are in the beginning of febuary, i would run 5w-30. im not really an expert on high milage stuff but i know when it comes to climate, u gotta up here in Canada. 5w in cold weather makes it easier for your starter to turn your engine compared to 10w oils. other then that theres no difference, but like i said im not an expert on high milage engines. __________________ eh 1970 Chevy C20 daily driver 1975 GMC Jimmy 4x4 project 1966 GMC C10 Dad's project

02-05-2009, 05:47 PM	#7
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: Oil Question? don't pour in the whole bottole of EOS on one oil chainge, that is way too much. 1/4 bottle is plenty. Pretty much all the diesel oils now have LESS zink than the gas oils do, so no point in that.



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