Wrong Oil? - JeepForum.com
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post #1 of 4 Old 04-10-2011, 06:43 PM Thread Starter
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Wrong Oil?

I'm trying to help a friend and I don't know much about GC's.

He says he has a 2001 WJ, straight six, and it's an auto.

When the Jeep is running for awhile, he feels like the oil starts running thin(loses it's consistency).

What should I tell him to do or look at or possibly run a different type of oil?

Thanks guys.


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post #2 of 4 Old 04-10-2011, 08:16 PM
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What makes him "feel like the oil is thin"? That is the least concrete statement I've seen on here in a while. The engine in his WJ is identical to that in your Wrangler, so you know plenty.

If the motor maintains pressure at rate approximately 10psi per 1000rpm when warm, there's no need to change viscosity. 4.0s like a high-zinc oil which can be hard to find. Stick with 10W-30 viscosity and look for API "SL" rated oils. My personal favorite in my 4.0 is Mobil1 High Mileage 10W-30 which runs smoothly and yields good wear numbers with a 6000 mile oil change interval.

If he wants to really know what is going on with his oil, then get a used oil analysis from somewhere like Blackstone labs. They will analyze it for wear metals, coolant contamination, viscosity, and TBN remaining to determine if the oil and engine are in good condition.

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post #3 of 4 Old 05-19-2011, 11:40 AM
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The recommended weight for the 4.0 is 10w30 and they run fantastic on it. I wonder if your friend could be running 5w30, I tried it once and drained it after a couple weeks. Engine was loud once it got warmed up and I didn't think ran as well either.

Like Bilzcat1 mentioned the 4.0's like the older additive packages. I am running Rotella 10w30, but anything in a high mileage forumula and not labeled "Resource Conserving" on the API donut is much more likely to be friendlier to the 4.0. Valvoline Max Life High Mileage is very common, not very expensive and has a great add pack for the 4.0, if you want synthetic the M1 HM bilzcat mentioned would be hard to beat.
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post #4 of 4 Old 05-19-2011, 11:43 AM
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I'm gonna jump on the AMSOIL train and tell your friend to do that. They have a special formula for the 4.0 Josh runs it.

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