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Unread 01-29-2013, 09:49 AM   #1
HeathFinnie
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Synthetic oil in an AMC 304?

I have a 76 CJ5 with a 304 V8 and 116,000 miles. Would it be worth switching to synthetic oil? I know it cleans better than conventional oil but also has some disadvantages (cost for one). I guess I'm just curious what all of you do... I also would still go 3-4000 miles between changes.

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Unread 01-29-2013, 10:36 AM   #2
Matt1981CJ7
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This is hotly debated topic.

I think studies prove that dinosaur oil produces more "sludge" in an engine, especially if oil changes are extended beyond every 3000 miles.

Some believe that synthetic oil is "thinner" and will cause leaks if used on an engine that has always had dinosaur goo. I'm not sure about that. If you're comparing oils of similar viscosity, how can one be "thinner" than the other?

I think the mixture of additives, particularly zinc, is what separates oils these days.

Matt
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Unread 01-29-2013, 11:11 AM   #3
HeathFinnie
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In regards to the leaks, the way I see that is if it leaks it was only a small matter of time before it would've leaked with conventional oil. It will just bring any problems to light faster.

I obviously want to extend the life of the 304 as long as I can and am thinking if the synthetic cleans better maybe that would be something I could do....?
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Unread 01-29-2013, 11:29 AM   #4
Matt1981CJ7
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Heath,

Do some reading on "ZDDP additive". My dyno guys were pretty adamant about using a high ZDDP oil like VR1, or similar, with my re-build.

Matt
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Unread 01-29-2013, 11:45 AM   #5
SuperSportCJ
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Its expensive but I am using Amsoil Z-ROD 10w-30 synthetic oil in my 304 that was rebuilt about 9k miles ago. No leaks and seems to be working fine. I have a catalytic converter I added to my aftermarket exhaust so I'm not sure how the additional zinc or ZDDP will affect it over time.
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Unread 01-29-2013, 11:57 AM   #6
HeathFinnie
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Thanks Matt, I will look at that.

I have no converter and just have two glass packs right now.
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Unread 01-29-2013, 11:57 AM   #7
uptillnow
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Great recommendation Matt,

Back in the ole’ days when the design of lubricating an engine wasn’t as sophisticated as it is in today’s engines, the actual lubrication was essential to engine life.

I used to use Torco motor oil with MPZ Molybdenum, Phosphorus and Zinc. What makes me laugh is sometimes in some applications the hydraulic lifters use to “bleed” down over night and clack like a “mad dog” in the morning.Once the lifters were pumped up this combination MPZ kept engines alive.

I agree with Matt that the ZDDP additive is an excellent addition to your oil changes.

UPTILLNOW
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Unread 01-29-2013, 01:46 PM   #8
lucdog
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I would stick with Conventional oils.

Here's why I feel that way. When regular oil is used sludge builds up on the inside of the engine, including gaskets (cork) When this happens the gaskets tend to dry out, age plays a role in this as well.Synthetic oils for whatever reason clean this sludge up. When there is no build up left on the gasket, they start to leak.
My oil choice would be, any oil from this link. http://www.penngrade1.com/
Valvoline 20w-50 racing oil
Or this with a zinc additive.

Attachment 553469

With a quart of this.

Attachment 553471

The reason for the zinc is to help prevent wear between the cam and lifters. The zinc has been, for the most part been removed from engine oil due to Emission regulations, and it's not needed in more Modern engines with overhead roller cam engines .

Bill
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Unread 01-29-2013, 01:53 PM   #9
Matt1981CJ7
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This is an interesting read that addresses the "sludge" issue.

Matt
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Unread 01-29-2013, 02:11 PM   #10
CSP
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Quote:
Originally Posted by Matt1981CJ7 View Post
Some believe that synthetic oil is "thinner" and will cause leaks if used on an engine that has always had dinosaur goo. I'm not sure about that. If you're comparing oils of similar viscosity, how can one be "thinner" than the other?
I think the correct term would be that synthetic is more slick than conventional and will more easily get into smaller voids. That's one of the reasons synthetic gear lube is recommended for many modern transmissions which have much tighter clearances between parts and bearings.
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Unread 01-29-2013, 02:22 PM   #11
Matt1981CJ7
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CSP,

That's probably a more accurate description.

Heath, not to confuse you any more, but I will admit that I did experience new leaks in my ol' 258 when I switched to synthetic. So there may be some validity to staying with dinosaur oil, as Bill suggests.

On a new, or rebuilt engine, synthetic, with a ZDDP additive, is probably the way to go, IMO.

Matt
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Unread 01-29-2013, 02:47 PM   #12
HeathFinnie
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Thanks!


The engine is a 12 year old rebuilt Crate 304 with about 35,000 miles.
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Unread 01-29-2013, 03:19 PM   #13
lucdog
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I thought I might add, I'm not anti synthetic. I use synthetic oil in most all of my 4 stroke air cooled engines , and have since they were new. This includes my 2000 Harley Davidson. I also use it in the transmission of my '02 Ford diesel truck, and in the rear differential. In the engine I use the Rotella pictured above (with the zinc additive) and change it at 3/4000 mile intervals.

Bill
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1957 WILLYS pickup, needs work.
1973 J 4000,
1978 CJ7 DD.
1979 CJ7 360, TH400/Quadratrac trail Jeep.
1979 J20
1980 CJ5 trail Jeep.
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1984 Grand Wagoneer, 1 ton axles, great 360/727, and a big a$& tree fell on it .
1989 YJ the CJ to YJ conversion.
2005 TJ Rubicon.
2011 Grand Cherokee Laredo 4x4, Mrs. LUCDOG's DD.
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