Prefered synthetic oil for 4.0?

In most instances, any oil brand nightmares you hear tell of are entirely anecdotal and happened to a guy who was a friend of another guy who was related to a customer of the barber shop your dad used in 1978. As I am an "old" guy, what used to be said was, never use detergent oil in a car that always was run on non-detergent oil. It would break up the sludge and plug your oil pump pick up and your engine would lose lubrication.
 
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The one time I used a synthetic, I developed a RMS leak. I changed back to Valvoline conventional and have had no RMS leak since. Anecdotal but true in my case. Coincidental? I don't care enough to try again.
 
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WallyWest said:
Because synthetic tends to clean everything real good in there, and on older engines that's not always a good thing. Can find it's way around seals that dino oil and a bit of sludge would not leak through.

I know there's endless arguments about that, but I've experienced it first hand.

That, and unless you have a high performance engine that strongly recommends or requires full synth from day 1, there's no real advantage to running it.
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Agree, I use full synthetic. Why use a blend? its like your not sure. Yes keeps engine very clean. Had a blazer v6 that used syn. in and under the valve cover looked brad new. And yes, you can go longer between changes, unless you like spending money
 
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Mjv said:
Pull the dip stick. If it looks dirty,it is. Change it. Dino, synthetic or blended.
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Sorry to disagree with this statement. There is no way to know the condition of used motor oil by looking at it.
 
Mjv said:
If it is darker than the oil you put in, would'nt you consider it dirty or burn't?
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I guess so. But if that's what we are considering, it is dirty after the first few hundred miles. Oil becomes darker than what we put in within the first few warm ups. I may not be understanding what exactly you see when you pull the stick out to look at your oil.
 
Oldguy said:
Agree, I use full synthetic. Why use a blend? its like your not sure.
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Blends extend oil life, give it somewhat better high temp protection, while still allowing some sludge buildup. In other words ideal for older high mileage engines.

Engines these days are usually engineered with tighter tolerances and higher compression, which is why many of them recommend full synth oil. I owned a Honda S2000 that came from the factory with Mobil 1 full synth and that's all I ever used in it. But using it in older engines, like the 4.0 in TJs is asking for trouble IMO.
 
I only run Mobile 1 in my v6.

Tractor supply has 5qt bottles of 10w30 Valvoline conventional on clearance for $11 at a few local stores here. Anything cheaper than Walmart Super Tech is a great deal.
 
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WallyWest said:
Because synthetic tends to clean everything real good in there, and on older engines that's not always a good thing. Can find it's way around seals that dino oil and a bit of sludge would not leak through.

I know there's endless arguments about that, but I've experienced it first hand.

That, and unless you have a high performance engine that strongly recommends or requires full synth from day 1, there's no real advantage to running it.
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Thanks for the explanation. And to be clear, I don't ask why because I question your opinion, I just like to learn these kinds of things.
 
WallyWest said:
Because synthetic tends to clean everything real good in there, and on older engines that's not always a good thing. Can find it's way around seals that dino oil and a bit of sludge would not leak through.
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Leaks are not necessarily caused by that. Some oils contain minimal seal conditioning additives and when the seals are old, that lack of seal conditioning additives can be the cause of a leak. My fix for that problem is to run a high-mileage conventional motor oil which has extra seal conditioning additives. Mobil Super conventional is one that works well for that job, it cured my BMW's RMS leak within a week. My general impression is few synthetics are aimed at high-mileage engines by including adequate additional amounts of seal conditioning additives.
 
Josh Harder said:
Looking to see what brand of synthetic oil most of you prefer?
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Up to this point I preferred Mobil 1 10W-30 for high mileage vehicles. It has a great additive package, it's a different formulation than other Mobil 1 branded oil, and even different than 5W-30 in the same group. In another vehicle I had this oil tested at various OCI's for about 80,000 miles, so I know objectively how good it is.

Now that sometimes the Jeep isn't driven daily, and often my wife drives in hurry-up mode before the engine reaches operating temp, I will be changing oil brand & weight for the next oil change interval. In a somewhat parallel thread, member @Tangerined shared a link to a very informative blog. Based on 540 RAT's thorough testing record, I'll be pouring AMSOIL Signature Series 5W-30 Synthetic Motor Oil next time.

For the confused among us, no amount of sludge is beneficial.
 
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The 4.0 does not require the most high tech super lux uber fancy oil. It neither has extreme tolerances nor high rpms to deal with. Any good oil with a good detergent package is more than acceptable for the engine. If anything, add a bit of diesel oil to up the wear resistance. Those fancy oils actually have reduced levels of wear protection since most new engines now use roller lifters and different cam lobe profiles.
 
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