I run Mobil 1 full synthetic in both my TJ and the wife's KJ. It's all personal choice. I would stick with a recognized brand (Valvoline, Castrol, Penzoil, Mobil, etc.). Bottom Line: As long as you are performing regular changes, the engine will be fine.
This has been covered over and over and over here. There are some answers regarding what is "best" however the question is what is "good enough".
Valvoline, Castrol, Pennzoil, and most others are Group III synthetics (not "true" synthetics. AMSOIL, Royal Purple, and Mobil1 are Group IV Synthetics (PAO Base Stock). Redline is a Group V synthetic (Ester Base Stock).
There has been a lot of data via Used Oil Analysis that shows that Mobil1 causes more iron wear within the 4.0L motor than many other oils (including Havoline and Shell Rotella mineral oils).
I use AMSOIL products exclusivly in my TJ.
Stay away from Slick50. It is bad stuff. Many additives will do nothing but harm your engine. If you really feel the need to clean and flush your engine, consider Auto-Rx. Auto-Rx is a Group V Ester product and not a detergent or acid like many other products.
James is right, there was a post about this yesterday, guy asked the same question. Just to drop my HO in here, I'm running Redline if all my vehicles and ATV's, I find it's worked the best so far.
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So what....... the Group V is the best? Is the Grouping typically labeled on the bottle?
From the above post, I take it that Redline is the best? Does it cost much more?
What are the oil change intervals?
Grouping of oil indicates the base stock used. Each has uses and applications and also has different features and benefits. Group I oils are for the most part obselete. Most regular mineral oils produced use Group II base stocks. Most oils currently marketed as "synthetic" are Group III. There has been some recent speculation that Mobil1 may indeed have switched to Group III base stocks. AMSOIL's XL series oils also use Group III base stocks.
Made through Solvent Freezing
Group I base oils are the least refined of all of the groups. They are usually a mix of different hydrocarbon chains with little or no uniformity. While some automotive oils on the market use Group I stocks, they are generally used in less demanding applications.
Made through Hydroprocessing and Refining
Group II base oils are common in mineral-based motor oils currently available on the market. They have fair to good performance in lubricating properties such as volatility, oxidative stability and flash/fire points. They have only fair performance in areas such as pour point, cold crank viscosity and extreme pressure wear.
Made through Hydroprocessing and Refining
Group III base oils are subjected to the highest level of mineral oil refining of the base oil groups. Although they are not chemically engineered, they offer good performance in a wide range of attributes as well as good molecular uniformity and stability. They are commonly mixed with additives and marketed as synthetic or semi-synthetic products. Group III base oil products have become more common in America during the past decade.
Made Through Chemical Reactions
Group IV base oils are chemically engineered synthetic base stocks. Polyalphaolefins (PAOs) are a common example of a synthetic base stock. Synthetics, when combined with additives, offer excellent performance over a wide range of lubricating properties. They have very stable chemical compositions and highly uniform molecular chains. Group IV base oils are becoming more common in synthetic and synthetic-blend products for automotive and industrial applications.
Made various ways
Group V base oils are used primarily in the creation of oil additives. Esters and polyolesters are both common Group V base oils used in the formulation of oil additives. Group V oils exhibit a wide variety of properties specific to each individual oil's formulation. Group V base oils are generally not used as base oils themselves, but add beneficial properties to other base oils.