Oil for a high mileage Pontiac 400

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Mar 26, 2003
Central Illinois
This is a never rebuilt, 120,000+ mile Pontiac 400 that runs good and does not burn oil. Mechanic has been using 30WT since he believes it is "better" for old engines. Car is run in MN and sometimes in cold weather
, road conditions permitting
. Stay with 30WT or what?

[ April 17, 2003, 08:52 PM: Message edited by: goatdude ]
Goatdude, you might want to try 15w-40. It is a little thinner when cold and a little thicker when hot compared to the 30wt you are using now. Any 15w-40 motor oil that is rated CI-4 and SL would be safe to use in your car. One item that you should be aware of is that if there is a lot of sludge in your engine than any oil that is rated for CI-4 can remove some of the crud fairly quickly so that in some cases so you might have to change the oil or at least the filter a little early after the first use of a CI-4/SL rated oil.

I think it would be a bad idea to use 5w-30 oil in an old Pontiac 400 cubic inch engine. 10w-30 or 10w-40 would be a better choice for an older large American V8 engine in very cold weather.
Schaeffer 10w30 blend, which will work very well in the occasional cold weather too. I had no problems with this oil when it hit -10F this winter here.

Is this the bigblock version? As I recall, GM made both BB and SB versions.

If so, I'd run 5W40 Redline, Delvac 1, Amsoil AME 15W40, or Schaeffer's 15W40 Blend in that engine for the summer and 10W30 (such as Amsoil ATM or Schaeffer #703) in the winter.

I compared the clearances in my 350 V8 Burb to that of a neighbor's 454 engined Burb and the
clearances were almost twice in the 454 compared to my 350. The neighbor is now running Delvac 1.
All Pontiac blocks were the same.

I run M1 15W-50 in my 135k Chrysler 383, but then I live in hotter-n-hell Texas. And will likely change to one of the recommendations as Molakule has given.
Two classifications for Pontiac V8s, large journal (421, 428 & 455) and small journal (ci up to 400). Blocks are the same overall dimensions externally. The 10W30 sounds good as it was not using oil before he went to straight 30wt and the lighter weight would be better for those few winter romps. Thanks for the replies.
If you are not buring oil at all and you want to stay with a 30wt, try one of the high mileage oils. They are a 30wt but on the heavier end and I've read some good UOA on them. I started using the Castrol GTX "high mileage" 10w-30 in my LS6(BB-454) after reading some good UOA. I was running Catrol GTX 10w-30 prior.
I am not a fan of thin oils for older engines......especially when the engine has higher mileage.....I personally would go with a 0W-40, 10W40 or 15W-40 oil...........not sure about synthetics from a sealing perspective.........Shaeffer's blend would IMO be the ticket for this application....heck, we used to use 20W-50 oils in these engines in the 70s when they were new....there were not 5W-30s or 10W-30s and when the 15W-40s came out we thought: Jeesh, what a thin oil !!!
Maybe he should run 10W30 from Sept to March since he likes taking the '69 GP out for a few winter romps and 15W40 as a "summer" oil? Probably had been using 10-30 for many years although we don't know the maint history. My Pontiac 400 ('67 GTO) run in IL seems to like a lighter oil for temps below 50 (clearances are .002-.0025" mains and .002"-.00225 rods, piston skirt clearance is .005"). Just went to Schaeffers #703 in my Pont 400. Had 15W40 pennzoil in there and that stuff took forever to come to temp and flow. My oil pressure would stay at 50 psi at idle (60 psi above 2000 rpm) at least 20 minutes after I started the engine!
A 40wt+ viscosity will be good for this old Pontiac. I also think this motor could really benefit from 2 treatments of auto-rx as the seals are well over 20 yrs old. If you want to run regular dino oil go for some 10w40 GTX in the winter and 20w50 in the summer. A fleet oil would be a good idea as long as the motor doesn't burn any oil. As for synthetic, 15w50 M1 would be the best choice, and would still give pretty cold start in cold weather.

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