Which oil is best?

Using synthetic oil won't cause your engine to "develop" leaks, but if your engine was seeping oil from hardened old seals before, it can cause more oil to get by the seal.

Synthetic oil has better cold flow properties and withstands heat better, but for most of us just using a cheap oil and changing it often due to the dusty/dirty off road environments our Jeeps see is the most cost effective option. I've actually run used oil analysis on my previous 4.0 Jeeps (not this one yet) and plain 'ole Pennzoil conventional 10w30 seemed to show the best wear numbers. With the 4.0L it doesn't really care what is in it, just change it regularly and keep it full. A high mileage oil like Valvoline MaxLife 10w30 contains seal conditioners that can actually slow down small leaks (like a seep) but won't fix bad leaks like a rear main seal or valve cover gasket that is significantly leaking.
 
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jeepguy03 said:
Using synthetic oil won't cause your engine to "develop" leaks, but if your engine was seeping oil from hardened old seals before, it can cause more oil to get by the seal.

Synthetic oil has better cold flow properties and withstands heat better, but for most of us just using a cheap oil and changing it often due to the dusty/dirty off road environments our Jeeps see is the most cost effective option. I've actually run used oil analysis on my previous 4.0 Jeeps (not this one yet) and plain 'ole Pennzoil conventional 10w30 seemed to show the best wear numbers. With the 4.0L it doesn't really care what is in it, just change it regularly and keep it full. A high mileage oil like Valvoline MaxLife 10w30 contains seal conditioners that can actually slow down small leaks (like a seep) but won't fix bad leaks like a rear main seal or valve cover gasket that is significantly leaking.
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I agree. I don’t think synthetic would make an engine leak, but my Jeep has 88k on the clock. And apparently the seals were hard enough from earlier use that they seeped quite easily.

I had very good results in my new Suburban, Sierra and Silverado once they were broken in. 😸

I wonder if how hot these things run has anything to do with seals hardening up. RMS leaks are quite common in these vehicles.
 
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williambmac said:
Severe duty is considered any condition where the vehicle is used for towing, mountain/hilly areas and high traffic areas where the vehicle is sitting in stop/go traffic or idling for extended period or traveling at higher rates of speed.

Being a GM technician, I can tell you draining the oil out of a 4k mile vs 7500 mile engine is a difference of night and day.

I can also tell you that the engines that see a more frequent service interval are the ones that last longer.

Most of the engines I tear down for internal problems are due to extended service intervals.

So to me changing the oil every 3-4k miles is not a waste of time, it's preventative maintainence that will extend the life of your vehicle.

GM vehicles have a oil life monitor system and yes you could get 7500-10000 miles before the oil life hits 0%, but we still recommend every 5k when using GM Dexos synthetic oil.
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Okay, but you didn't answer my question: Why is the East Coast is considered "severe duty" driving?

I have been on the East Coast my entire life, and I have never heard that. Perhaps you know something I don't?
 
3500, 4000, 5500, 7500?
Every 5000, easy to remember 5k,10k,15k,20k, etc.

Also, IMO, just changing it is more important than what type you put in.
My daughters 2010 Kia has 270K miles, all on Walmart oil and fram filters (every 5k miles)
 
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Rooscooter said:
Interesting..... I've used the Pennzoil Platinum Synthetic high milage formula for a couple changes now and haven't noticed any lifter noise. I'll have to pay closer attention maybe....
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I've used the same and have had nothing but good results from this same oil. No lifter noise/tick or anything. The major leak i recently had, I thought was a rear main seal but it ended up being the oil pan itself.

Has anyone tried CBD oil, will the TJ fly?
 
jeepguy03 said:
Using synthetic oil won't cause your engine to "develop" leaks, but if your engine was seeping oil from hardened old seals before, it can cause more oil to get by the seal.
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My RMS was not leaking.
I changed to a 10w-30 full synthetic.
RMS was leaking, leaving drops on the floor.
I changed back to 10w-30 conventional.
RMS is not leaking, no drops on the floor, RMS area is dry.

The cause/effect seems pretty clear and we might be splitting hairs about causing leaks to "develop".
 
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