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Unread 03-12-2006, 11:26 PM   #1
Budman21901
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Synthetic Oil

I am a advocate of sythetic oil, so when i purchased my jeep 3days ago i was suprised that they told me No synthetic oil. They told me the I-6 has wet seals, and aluminum block, and my old engine was dry seals, and cast iron block. Does this hold any truth at all? Sound's almost like a blinker fuid story to me, but it was told by mechanic's. Does any of this ring true??

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Unread 03-12-2006, 11:30 PM   #2
Tshark299
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Don't know anything about seals but the 4.0's block and head are both cast iron.

Alot of people run synthetic oil in 4.0s seemingly without any problems...
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Unread 03-17-2006, 12:09 PM   #3
Haik
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Quote:
Originally Posted by Budman21901
I am a advocate of sythetic oil, so when i purchased my jeep 3days ago i was suprised that they told me No synthetic oil. They told me the I-6 has wet seals, and aluminum block, and my old engine was dry seals, and cast iron block. Does this hold any truth at all? Sound's almost like a blinker fuid story to me, but it was told by mechanic's. Does any of this ring true??

only difference between regular oils and synthetic oils is that the synthetic oils undergo extra processing to remove parafin waxes (the crap) from the oil. And of course, they add a blend of chemicals as well.

whoever told you NOT to run synthetic is smokin crack. My jeep instantly thanked me when I did the switch, but then again, I live in Canada. Synthetics are fantastic in cold weather.
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Unread 03-17-2006, 03:14 PM   #4
Bgeddes
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A lot of people that have switched an older engine from dino oil to synthetic have developed leaks.
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Unread 03-17-2006, 03:44 PM   #5
98JEEPTJ
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Sounds like the fella you talked to might have been thinking of the radiator fluid not the engine oil. What year and motor you got??
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Unread 03-17-2006, 06:57 PM   #6
cjjeeper258
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I would call bs on whoever told you that.

I would not run it in a brand new engine since I want the rings to seal quickly. After 10-15K miles, I would make the switch.

As has been stated in previous posts:

Synthetic is great. Period
Its great in cold weather

Your vehicle may run noticably better and may even pick up a few MPG since synthetic is better than dino oil. I have had 2 vehicles run better and pick up 2 MPG.

However Tshark299 makes a valid point. If you have bad seals (i.e. High mileage Motor) synthetic will leak out since its thinner. I have had firsthand experience.

Engine metal composition has nothing to do with what oil you run. It does have a relevance what coolant you run though from what I have read.
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Unread 03-17-2006, 09:12 PM   #7
dsl4me
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Quote:
Originally Posted by Bgeddes
A lot of people that have switched an older engine from dino oil to synthetic have developed leaks.
Have switched at least 2 with 75K and one with 110K over to synthetic and haven't had leak issues. Just the initial change should be done soon since the synthetic has better cleaning properties. Loosens any sediment up.
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Unread 03-18-2006, 11:41 AM   #8
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My 4.0L loves synthetic. I even talked directly to my dealer and DC about it. I run Mobil 1 5-40W Truck and SUV full synthetic. Switched around 70,000 miles (87,000 now) and it runs great, no leaks good starts, etc. Whoever told you that has no clue.

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Unread 03-19-2006, 10:28 AM   #9
hutchmanhd
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Here is a link to a very well written article about synthetic oil. It is slanted towards motorcycles, but some good info anyway:

http://motorcycleinfo.calsci.com/Oils1.html

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Unread 03-20-2006, 12:36 PM   #10
Fullsize_CJ5
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You can switch to synthetic oil, with no problems. I'd suggest waiting untill you have at least 2000 miles or so on the new engine before you switch. Synthetic oil lubes so well your rings will have trouble seating on the cylinder walls, wait till the engine is "broke in" then change to synthetic.
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Unread 03-21-2006, 06:39 AM   #11
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I have a '96 Ford Contour 2.0 that I've had since 18K on it. I've run synthetics in it except a two or three times. Once was a blend. I notice a 2 mpg gain between synthetics vs conventional oils. I also notice that in my 2000 Contour SVT. The '96 has 168K on it. The engine does have some eletrical problems, but looked good when I pulled the valve cover. I've used Castrol, Mobil 1 and now Penzoil. That engine doesn't like heavier weight oils. It ran a bit rough on 15W-40. I think you could run that in the 4.0L though. Although you might not gain the mpg. I ran 10W-30 and 10W-40 in a 351W and also 20W-50 conventional oil. I did notice a -2 mpg with the 20W-50. Conventional oils have vastly improve from what I hear. The better ones are nearing the performance of synthetics. Still, I use synthetics. Also, don't forget a good oil filter. Wix, Napa, Balwin, Puralator, Mobil 1 are good ones. I usually run mine at least 5K between oil changes. I've gone 10K at times. It depends if your driving highway miles or city. Also, on the condition of the engine. Plus, if you still in warranty, I would look at the service intervals and not exceed them. Usually they are 5K to 7.5K.
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