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Unread 10-26-2011, 11:49 AM   #1
salsomano1a
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synthetic oil question

i have a 91 yj 4.0 the engine has 98,000 miles on it, it has 5-20 regular oil, i want it to know if i could use synthetic oil in it, all help will be apreciatted, thanks

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Unread 10-26-2011, 11:52 AM   #2
waif69
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You could put synthetic oil in it, but IMHO you would be wasting your money. I use sythetic in my vehicles with new engines, but not in an engine that will burn some and leak some. AFAIC, all YJs will burn some and leak some unless the engine has been recently rebuilt.
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Unread 10-26-2011, 11:53 AM   #3
salsomano1a
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would it give me better gas mileage?
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Unread 10-26-2011, 11:57 AM   #4
MLJeeper
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No you will not see an appreciable gain in gas mileage. I run synthetic and will use nothing else in any of my vehicles.
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Unread 10-26-2011, 12:13 PM   #5
Que89YJ
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Synthetics do not break down so you can go much much further on oil changes and are more resistant to absorbing moisture so prevent the build up of sludge. I run nothing but synthetic in my vehicles. More because I am lazy about changing the oil and I can go 7000 or more on an oil change. There is nothing wrong with running synthetic on your Jeep even with higher miles as long as like was previously stated you burn or leak oil.
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Unread 10-26-2011, 12:19 PM   #6
RowJ
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Age old question.... boils down to your personal preference. Pay more and run longer or change more often.
I too like synthetics, but work for an oil company and get them for cost!

BUT.... running 5w-20 may be a mistake.
Not what your engine calls for..... will not increase mileage appriciably.... unnecessary in your warm climate.......
and could increase wear and tear on an engine designed to run 4000+ rpm.

I would not do it in my area, especially in the summer months..... but it's your money.... your choice.

RJ
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Unread 10-26-2011, 12:23 PM   #7
MLJeeper
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True, I run 10-30.
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Any video of the sound?
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Unread 10-26-2011, 12:32 PM   #8
Que89YJ
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I didn't catch the 5w 20. 5/20 is really light oil and the engine needs to be designed for it. The tolerance are just not that tight. It is necessary to run the light weights on the newer cars(Like my Charger RT) to allow the lockup in the Multi cylinder displacement. Not something you should be doing. The lighter weights do not adhere as log to surfaces and leak down faster from the top of the engine. 10/40.
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Unread 10-26-2011, 01:36 PM   #9
salsomano1a
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so RowJ which one you recomend me my friend??
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Unread 10-26-2011, 01:46 PM   #10
91BoD
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10/30 or 10/40
is the recommended oil viscosity. Many people run diesel 10/40 for the extra detergents and Zinc.

Run synthetic if you do not burn or leak oil. You will leak more oil with a synthetic because the actual independant oil molecules are smaller and you don't want to burn your expensive oil.

Do not run a brand new engine on synthetic, it's lubricating properties are too great and do not allow the rings to seat. Run dino oil or conventional for X miles. (depends on oil engine and operating conditions, standard is 2-5k)

I personally walk in and pick what is on sale, but I don't care about my 4cyl and she doesn't seem to mind.
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Unread 10-26-2011, 01:49 PM   #11
Que89YJ
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http://www.mobiloil.com/usa-english/...ics/myths.aspx
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Unread 10-26-2011, 01:51 PM   #12
RowJ
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I use 10w-30.
We had over 70 consecutive days this summer that reached more than 100*. I had an oil change due about 3 weeks into the heat wave and tried my 15w-40 diesel oil..... hoping to cool the engine down below 210* on the Hwy. Did not work. With either oil, my coolant got to about 220* and stayed there.

I recommend 10w-30 for everyone. Hard to go against the factory engineers on oil viscosity, since so many factors enter into their recommendation.

Probably biggest plus to synthetic oils is 'thermal stability'. They resist thinning out when your engine gets very hot.
They tend to just sit there and do their thing.... as well at 110* OAT as they do at 60* OAT.
Because of this fact, they are less likely to break down and leave gum, laquor or carbon deposits.

But any good quality mineral oil (non synthetic) will also get the job done very well if changed every 3-5,000 miles.
Of the non synthetic, competitors oils I have tested, I think todays Chevron Delo 400 is the best I've seen in recent yrs.

RJ
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Unread 10-26-2011, 02:02 PM   #13
Que89YJ
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Just talked to a trans guy here at work. I have to qualify it. Seal leak is an issue as well as oil burn. Loser tolerances and old designed seals can lead to issues with synthetics.
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Unread 10-26-2011, 02:03 PM   #14
RowJ
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Quote:
Originally Posted by 91BoD View Post
..... You will leak more oil with a synthetic because the actual independant oil molecules are smaller ......
Do not run a brand new engine on synthetic, it's lubricating properties are too great and do not allow the rings to seat......
Sorry but these are two of the many misconceptions about synthetic oil!

1- Synthetic oil molecules are not smaller. Synthetics tend to leak because there is no impurities in it.
The impurities in mineral oils tend to act like a plug for areas prone to leaking.

2- You can run synthetic oil in a new engine and the rings will seal. It just takes longer.
Warren Johnson, famous Pro Stock drag racer told me he breaks in an engine on the same synthetic oil he races with. He never would tell me why!

But...to repeat many here.... Jeeps seem to do well and enjoy just about any type and brand oil.
With the higher rpm's on Jeep engines, the key IMO, is to change the oil frequently.

RJ
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Unread 10-26-2011, 02:07 PM   #15
MONSooNmonkey
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Quote:
Originally Posted by salsomano1a View Post
i have a 91 yj 4.0 the engine has 98,000 miles on it, it has 5-20 regular oil, i want it to know if i could use synthetic oil in it, all help will be apreciatted, thanks
Yes you could, just be aware that synthetic oils clean the engine MUCH better than dyno juice and COULD CAUSE seals that were clogged with sludge to start leaking.

No the synthetic didn't cause the leak it was already damaged prior to the oil change over.

When doing this type of oil change I like to buy two oil changes of the new type. Go warm up the vehicle with a nice ride 10+ miles, park it where you'll change the oil. Drain oil, refill with synthetic, drive for a few days or 200 miles or so, drain oil and change with the second oil change you bought.

Your engine should now be as clean as its going to get, the first short stop change was to remove the gunk that the synthetic cleaned away.
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