I have a 69 350/350 that is supposed to have 39,000 actual miles on it. I bought it 2 weeks ago and the oil was clean, I have driven it about 300 miles and the oil is quite dirty already. Do you recomend some type of flush or just another oil change? Do you recomend synthetic oils for the engine, or the gear boxes?
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Re: oil changes
Tom-----
Old technology engines have a habit of "turning the oil dirty" rather quickly. The 1969 L-46 would be especially susceptible to this. That's because that engine used forged pistons which are set up with piston-to-bore clearances considerably greater than engines with cast pistons. Subsequent to the engine coming up to operating temperature, the clearances are "tightened up". However, during the warm-up period, considerable combustion product leakage past the rings occurs. Also, considerable wear of the pistons, especially ring lands, occurs during the warm-up period and this contributes to long-term leakage of combustion products into the crankcase even after the engine is at operating temperature. Quite frankly, 40,000 miles is probably beyond the SERVICE life of forged pistons and, particularly, 1969-era forged pistons.
The above is the primary reason that GM hasn't used a forged piston in a PRODUCTION V-8 engine since 1980. They have used them in some SERVICE engine assemblies (which don't have to meet the same durability validation testing as PRODUCTION engines), but no PRODUCTION V-8 engines.
I always recommend the use of synthetic oil for engines and transmissions. I don't use it for Corvette rear ends, though.In Appreciation of John Hinckley -
Re: oil changes
Joe,
I have 66 427/390. Would you use synthetic oil in this engine. I have 76,000 primarily gentle miles on engine and it loses minor amount of oil. Which oil would you recommend and what replacement time frame would you use. Thanks.
regards, Steve PettitComment
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Re: oil changes
Steve-----
With an engine that's been run for 76,000 miles on conventional oil, I don't think that you have a lot to gain by converting to synthetic. I'd probably continue to use conventional oil in such an engine. However, if and when you rebuild the engine I would definitely convert to synthetic. I would recommend Mobil 1 10W-30, and as far as REGULAR change interval goes, I'd change it at 3,000 miles or 1 year.
In my "ZL-1", I plan to use Mobil 1 10W-30, so, "I practice what I preach".In Appreciation of John HinckleyComment
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Re: oil changes
Joe,
Your comment "Quite frankly 40,000 miles is probably beyond the Sevice life of forged pistons and, particularly, 1969-era forged pistons." Request what this implies?
I have a original owner 68 with forged pistons, 327/350, and it has 96K on it now. My oil stays pretty clean between oil changes and it is very clean immediately after an oil change. This original engine runs very good.
Reference GM not using a forged piston in a production V-8 engine since 1980. I requested some informantion from Chevrolet on my 1985 Corvette and recievied a Motor Vehicle Specifications booklet that has 32 pages. On page 3 Engine-Pistons it states Impacted forged aluminum, .579 (20.4). Until getting this booklet I thought I had cast pistons in my 85 Vette. If this is true, I have about 102K on these forged pistons and the oil in the 85 stays clean as well.Comment
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Re: oil changes
Jim------
By "service life" I'm referring to the point at which the parts exceed the service limit specifications with respect to, at least, one parameter. That does not mean that the part stops functioning at that point. If you were to remove the pistons from your car my expectation is that at least one of the service limits, likley including the ring land specs, would be outside of the service limits. I would not suggest that you do so, though. If the engine is performing satisfactorily, I'd leave well enough alone.
As far as the 1985 pistons go, I am aware of the AMA specifications which show these pistons to be impact extruded aluminum (i.e. forged). However, I don't think that these pistons actually are a forged piston. There are quite a few inaccuracies to be found in the AMA specs which most folks consider to be "authoritative". I will say, though, that it IS possible that the 84-85 pistons were forged. If so, it represents an exception to the "no-use-of-forged pistons-in-V-8 engines-after-1980" statement that I made. If this is an exception, there aren't many.
Also, come to think of it, I've noticed quite a few early C4s "smoking" as they go down the road. So, maybe they DID use forged pistons!In Appreciation of John HinckleyComment
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Correction
Jim-----
I did a little further research on the 1985 piston issue. The 1984-85 Corvette pistons WERE forged. They were the same pieces used on 1973-80 L-82 engines. So, I'm going to have to modify the year that GM stopped using forged pistons in future information that I provide. Forged pistons MAY have ben used for 1986-88 L-98s, too, but I haven't confirmed that. They were NOT used in Corvette engines after 1988, though, including LT-5, LT-4 and LS-6.In Appreciation of John HinckleyComment
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I would suggest you change the oil when it
gets dirty. Not dirty looking. If your pcv system is working and you don't drive over 1000 miles a year, and you don't sit in the garage and fire it up for a few minutes to show your neighbor how it sounds once a day, give the environment and your wallet a break and change it every two years. You will not live long enough to wear it out if your are over 50 now.
Same with synthetic oil. This will never be a high milage car so any potential benefits derived from using the expensive stuff will not be realized in your lifetime.
By the way, detergent oil has a way of getting very dirty, very quickly after an oil change if it is doing what it is designed to do which is CLEANING!Comment
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Re: oil changes
Joe:
I've used synthetic oil for over 10 years, and believe they do offer benefits over conventional oils, especially in high heat situations, extreme cold situations (flow characteristics) and intial starting.
I noticed you mentioned that you use synthetics in the motor and trans, but not the rear. Why would they not offer some benefits for the rear as well?
Just curious to hear your view on that.
Regards,
RichComment
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Re: oil changes
Tom, it is dangerous to be on the other side of an issue from 'Da Man' , but if it were me, I probably would NOT use synthetic oil in this specific case.
It is true that the oil will get dirty fast if the detergent package is doing its job, but it sounds like you may have experienced one of the classic "things to do" to sell a car...change the oil. If the car has not had timely oil and filter changes in the past, you may have accumulated "gunk" inside the engine. That could be another reason why the oil got "quite dirty" in 300 miles.
I completely agree with Joe on the benefits of using synthetic oil for a vehicle that can see hard use, and is to maintain new performance for a long time. In my opinion, a new or late model Corvette is a perfect application for sythetic oil. My C4 was fed Mobil 1 from Day One, and it ran better than new with 49K miles...I'll use it on my 2006.
However, for a car as old as yours with the original engine build, I believe changing to synthetic oil at this late date may cause you oil leaks and other problems. I would continue to use the same grade mineral oil, changing the oil and filter frequently.
I have used Pennzoil 10W30 or 5W30, changing oil and filter every 5000 miles on my "other" cars, and the bodies crater before the engines (150K, 160K, 101K and counting). For your car, I would probably use Pennzoil 10W30 and change oil and filter every 3000 miles or 6 months, whichever comes first.
If you ever rebuild the engine, then you could consider synthetic oil AFTER the engine has been well broken in.Comment
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Synthetic in a new Truck
I just purchased a new Chev truck. I was considering using Synthetic oil. Is there a break-in period (time or miles) which normal oil should be used before switching to synthetic oil.Comment
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Re: Synthetic in a new Truck
Ronnie, there are folks here that know more about this than I, but my understanding is that new GM engines are "broken in", that is the rings have seated less than a half hour after startup; i.e, the rings are seated before the vehicles leave the factory.
I would say your truck could probably be changed to synthetic oil at the first scheduled oil change. What does your owners manual say about using synthetic oil?Comment
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Re: oil changes
Rich-----
Synthetics might offer advantages for the rear end lubricant, too. However, for me, the GM #1052271 is so time-proven and works so well that I'm not ready to switch.In Appreciation of John HinckleyComment
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Re: Synthetic in a new Truck
Ronnie:
I let my 2000 Tahoe "Break In" when new, for 1500 miles, and have used Mobil 1 synthetic 10-30 and 5-30 (winter) ever since. Change every 3 - 4K, but now am extending my oil change intervals to 5K as the oil really does not look very dirty to me, even at 5K. Manual says to use the oil life indicator, but I do not use that at all.
Now have 49K miles on the car, and it has never used a drop of oil between changes.
I am also using a Purolater "Pure One" oil filter lately, and it seems to me that the oil stays cleaner looking right to the point when I have to change it.
I also run synthetic in my 98 BMW528i. Castrol GTX5-50 because it is the right viscosity spread for my engine. I change the oil twice per year as I only drive it 5-6K miles per year. This one has never used a drop of oil either between changes.
I run Mobil 1 10-30 in my 68 Vette with a Puralator Pure One filter. Engine has about 4K miles on it after a full rebuild (327/350), oil change interval is once per year, but I intend to drive it just on nice weather weekends, so I figure I'll do about a thousand miles per year.
Here's some interesting links on some filter studies and oil studies for those who may be interested.
Regards,
RichComment
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Re: oil changes
Thanks Joe, makes sense. If it ain't broke, don't fix it.
Regards,
RichComment
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